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android / platform / packages / modules / DnsResolver / refs/tags/platform-tools-29.0.4 / . / res_cache.cpp
blob: 83ec09f7e283ad110290699b2de82511bcaf81c6 [file] [log] [blame]
/*
* Copyright (C) 2008 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#define LOG_TAG "resolv"
#include "resolv_cache.h"
#include <resolv.h>
#include <stdarg.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <algorithm>
#include <mutex>
#include <set>
#include <string>
#include <unordered_map>
#include <vector>
#include <arpa/inet.h>
#include <arpa/nameser.h>
#include <errno.h>
#include <linux/if.h>
#include <net/if.h>
#include <netdb.h>
#include <android-base/logging.h>
#include <android-base/parseint.h>
#include <android-base/stringprintf.h>
#include <android-base/strings.h>
#include <android-base/thread_annotations.h>
#include <android/multinetwork.h> // ResNsendFlags
#include <server_configurable_flags/get_flags.h>
#include "res_state_ext.h"
#include "resolv_private.h"
// NOTE: verbose logging MUST NOT be left enabled in production binaries.
// It floods logs at high rate, and can leak privacy-sensitive information.
constexpr bool kDumpData = false;
/* This code implements a small and *simple* DNS resolver cache.
*
* It is only used to cache DNS answers for a time defined by the smallest TTL
* among the answer records in order to reduce DNS traffic. It is not supposed
* to be a full DNS cache, since we plan to implement that in the future in a
* dedicated process running on the system.
*
* Note that its design is kept simple very intentionally, i.e.:
*
* - it takes raw DNS query packet data as input, and returns raw DNS
* answer packet data as output
*
* (this means that two similar queries that encode the DNS name
* differently will be treated distinctly).
*
* the smallest TTL value among the answer records are used as the time
* to keep an answer in the cache.
*
* this is bad, but we absolutely want to avoid parsing the answer packets
* (and should be solved by the later full DNS cache process).
*
* - the implementation is just a (query-data) => (answer-data) hash table
* with a trivial least-recently-used expiration policy.
*
* Doing this keeps the code simple and avoids to deal with a lot of things
* that a full DNS cache is expected to do.
*
* The API is also very simple:
*
* - the client calls _resolv_cache_get() to obtain a handle to the cache.
* this will initialize the cache on first usage. the result can be NULL
* if the cache is disabled.
*
* - the client calls resolv_cache_lookup() before performing a query
*
* if the function returns RESOLV_CACHE_FOUND, a copy of the answer data
* has been copied into the client-provided answer buffer.
*
* if the function returns RESOLV_CACHE_NOTFOUND, the client should perform
* a request normally, *then* call resolv_cache_add() to add the received
* answer to the cache.
*
* if the function returns RESOLV_CACHE_UNSUPPORTED, the client should
* perform a request normally, and *not* call resolv_cache_add()
*
* note that RESOLV_CACHE_UNSUPPORTED is also returned if the answer buffer
* is too short to accomodate the cached result.
*/
/* default number of entries kept in the cache. This value has been
* determined by browsing through various sites and counting the number
* of corresponding requests. Keep in mind that our framework is currently
* performing two requests per name lookup (one for IPv4, the other for IPv6)
*
* www.google.com 4
* www.ysearch.com 6
* www.amazon.com 8
* www.nytimes.com 22
* www.espn.com 28
* www.msn.com 28
* www.lemonde.fr 35
*
* (determined in 2009-2-17 from Paris, France, results may vary depending
* on location)
*
* most high-level websites use lots of media/ad servers with different names
* but these are generally reused when browsing through the site.
*
* As such, a value of 64 should be relatively comfortable at the moment.
*
* ******************************************
* * NOTE - this has changed.
* * 1) we've added IPv6 support so each dns query results in 2 responses
* * 2) we've made this a system-wide cache, so the cost is less (it's not
* * duplicated in each process) and the need is greater (more processes
* * making different requests).
* * Upping by 2x for IPv6
* * Upping by another 5x for the centralized nature
* *****************************************
*/
#define CONFIG_MAX_ENTRIES (64 * 2 * 5)
/** BOUNDED BUFFER FORMATTING **/
/* technical note:
*
* the following debugging routines are used to append data to a bounded
* buffer they take two parameters that are:
*
* - p : a pointer to the current cursor position in the buffer
* this value is initially set to the buffer's address.
*
* - end : the address of the buffer's limit, i.e. of the first byte
* after the buffer. this address should never be touched.
*
* IMPORTANT: it is assumed that end > buffer_address, i.e.
* that the buffer is at least one byte.
*
* the bprint_x() functions return the new value of 'p' after the data
* has been appended, and also ensure the following:
*
* - the returned value will never be strictly greater than 'end'
*
* - a return value equal to 'end' means that truncation occurred
* (in which case, end[-1] will be set to 0)
*
* - after returning from a bprint_x() function, the content of the buffer
* is always 0-terminated, even in the event of truncation.
*
* these conventions allow you to call bprint_x() functions multiple times and
* only check for truncation at the end of the sequence, as in:
*
* char buff[1000], *p = buff, *end = p + sizeof(buff);
*
* p = bprint_c(p, end, '"');
* p = bprint_s(p, end, my_string);
* p = bprint_c(p, end, '"');
*
* if (p >= end) {
* // buffer was too small
* }
*
* printf( "%s", buff );
*/
/* Defaults used for initializing res_params */
// If successes * 100 / total_samples is less than this value, the server is considered failing
#define SUCCESS_THRESHOLD 75
// Sample validity in seconds. Set to -1 to disable skipping failing servers.
#define NSSAMPLE_VALIDITY 1800
/* add a char to a bounded buffer */
static char* bprint_c(char* p, char* end, int c) {
if (p < end) {
if (p + 1 == end)
*p++ = 0;
else {
*p++ = (char) c;
*p = 0;
}
}
return p;
}
/* add a sequence of bytes to a bounded buffer */
static char* bprint_b(char* p, char* end, const char* buf, int len) {
int avail = end - p;
if (avail <= 0 || len <= 0) return p;
if (avail > len) avail = len;
memcpy(p, buf, avail);
p += avail;
if (p < end)
p[0] = 0;
else
end[-1] = 0;
return p;
}
/* add a string to a bounded buffer */
static char* bprint_s(char* p, char* end, const char* str) {
return bprint_b(p, end, str, strlen(str));
}
/* add a formatted string to a bounded buffer */
static char* bprint(char* p, char* end, const char* format, ...) {
int avail, n;
va_list args;
avail = end - p;
if (avail <= 0) return p;
va_start(args, format);
n = vsnprintf(p, avail, format, args);
va_end(args);
/* certain C libraries return -1 in case of truncation */
if (n < 0 || n > avail) n = avail;
p += n;
/* certain C libraries do not zero-terminate in case of truncation */
if (p == end) p[-1] = 0;
return p;
}
/* add a hex value to a bounded buffer, up to 8 digits */
static char* bprint_hex(char* p, char* end, unsigned value, int numDigits) {
char text[sizeof(unsigned) * 2];
int nn = 0;
while (numDigits-- > 0) {
text[nn++] = "0123456789abcdef"[(value >> (numDigits * 4)) & 15];
}
return bprint_b(p, end, text, nn);
}
/* add the hexadecimal dump of some memory area to a bounded buffer */
static char* bprint_hexdump(char* p, char* end, const uint8_t* data, int datalen) {
int lineSize = 16;
while (datalen > 0) {
int avail = datalen;
int nn;
if (avail > lineSize) avail = lineSize;
for (nn = 0; nn < avail; nn++) {
if (nn > 0) p = bprint_c(p, end, ' ');
p = bprint_hex(p, end, data[nn], 2);
}
for (; nn < lineSize; nn++) {
p = bprint_s(p, end, " ");
}
p = bprint_s(p, end, " ");
for (nn = 0; nn < avail; nn++) {
int c = data[nn];
if (c < 32 || c > 127) c = '.';
p = bprint_c(p, end, c);
}
p = bprint_c(p, end, '\n');
data += avail;
datalen -= avail;
}
return p;
}
/* dump the content of a query of packet to the log */
static void dump_bytes(const uint8_t* base, int len) {
if (!kDumpData) return;
char buff[1024];
char *p = buff, *end = p + sizeof(buff);
p = bprint_hexdump(p, end, base, len);
LOG(INFO) << __func__ << ": " << buff;
}
static time_t _time_now(void) {
struct timeval tv;
gettimeofday(&tv, NULL);
return tv.tv_sec;
}
/* reminder: the general format of a DNS packet is the following:
*
* HEADER (12 bytes)
* QUESTION (variable)
* ANSWER (variable)
* AUTHORITY (variable)
* ADDITIONNAL (variable)
*
* the HEADER is made of:
*
* ID : 16 : 16-bit unique query identification field
*
* QR : 1 : set to 0 for queries, and 1 for responses
* Opcode : 4 : set to 0 for queries
* AA : 1 : set to 0 for queries
* TC : 1 : truncation flag, will be set to 0 in queries
* RD : 1 : recursion desired
*
* RA : 1 : recursion available (0 in queries)
* Z : 3 : three reserved zero bits
* RCODE : 4 : response code (always 0=NOERROR in queries)
*
* QDCount: 16 : question count
* ANCount: 16 : Answer count (0 in queries)
* NSCount: 16: Authority Record count (0 in queries)
* ARCount: 16: Additionnal Record count (0 in queries)
*
* the QUESTION is made of QDCount Question Record (QRs)
* the ANSWER is made of ANCount RRs
* the AUTHORITY is made of NSCount RRs
* the ADDITIONNAL is made of ARCount RRs
*
* Each Question Record (QR) is made of:
*
* QNAME : variable : Query DNS NAME
* TYPE : 16 : type of query (A=1, PTR=12, MX=15, AAAA=28, ALL=255)
* CLASS : 16 : class of query (IN=1)
*
* Each Resource Record (RR) is made of:
*
* NAME : variable : DNS NAME
* TYPE : 16 : type of query (A=1, PTR=12, MX=15, AAAA=28, ALL=255)
* CLASS : 16 : class of query (IN=1)
* TTL : 32 : seconds to cache this RR (0=none)
* RDLENGTH: 16 : size of RDDATA in bytes
* RDDATA : variable : RR data (depends on TYPE)
*
* Each QNAME contains a domain name encoded as a sequence of 'labels'
* terminated by a zero. Each label has the following format:
*
* LEN : 8 : lenght of label (MUST be < 64)
* NAME : 8*LEN : label length (must exclude dots)
*
* A value of 0 in the encoding is interpreted as the 'root' domain and
* terminates the encoding. So 'www.android.com' will be encoded as:
*
* <3>www<7>android<3>com<0>
*
* Where <n> represents the byte with value 'n'
*
* Each NAME reflects the QNAME of the question, but has a slightly more
* complex encoding in order to provide message compression. This is achieved
* by using a 2-byte pointer, with format:
*
* TYPE : 2 : 0b11 to indicate a pointer, 0b01 and 0b10 are reserved
* OFFSET : 14 : offset to another part of the DNS packet
*
* The offset is relative to the start of the DNS packet and must point
* A pointer terminates the encoding.
*
* The NAME can be encoded in one of the following formats:
*
* - a sequence of simple labels terminated by 0 (like QNAMEs)
* - a single pointer
* - a sequence of simple labels terminated by a pointer
*
* A pointer shall always point to either a pointer of a sequence of
* labels (which can themselves be terminated by either a 0 or a pointer)
*
* The expanded length of a given domain name should not exceed 255 bytes.
*
* NOTE: we don't parse the answer packets, so don't need to deal with NAME
* records, only QNAMEs.
*/
#define DNS_HEADER_SIZE 12
#define DNS_TYPE_A "\00\01" /* big-endian decimal 1 */
#define DNS_TYPE_PTR "\00\014" /* big-endian decimal 12 */
#define DNS_TYPE_MX "\00\017" /* big-endian decimal 15 */
#define DNS_TYPE_AAAA "\00\034" /* big-endian decimal 28 */
#define DNS_TYPE_ALL "\00\0377" /* big-endian decimal 255 */
#define DNS_CLASS_IN "\00\01" /* big-endian decimal 1 */
typedef struct {
const uint8_t* base;
const uint8_t* end;
const uint8_t* cursor;
} DnsPacket;
static void _dnsPacket_init(DnsPacket* packet, const uint8_t* buff, int bufflen) {
packet->base = buff;
packet->end = buff + bufflen;
packet->cursor = buff;
}
static void _dnsPacket_rewind(DnsPacket* packet) {
packet->cursor = packet->base;
}
static void _dnsPacket_skip(DnsPacket* packet, int count) {
const uint8_t* p = packet->cursor + count;
if (p > packet->end) p = packet->end;
packet->cursor = p;
}
static int _dnsPacket_readInt16(DnsPacket* packet) {
const uint8_t* p = packet->cursor;
if (p + 2 > packet->end) return -1;
packet->cursor = p + 2;
return (p[0] << 8) | p[1];
}
/** QUERY CHECKING **/
/* check bytes in a dns packet. returns 1 on success, 0 on failure.
* the cursor is only advanced in the case of success
*/
static int _dnsPacket_checkBytes(DnsPacket* packet, int numBytes, const void* bytes) {
const uint8_t* p = packet->cursor;
if (p + numBytes > packet->end) return 0;
if (memcmp(p, bytes, numBytes) != 0) return 0;
packet->cursor = p + numBytes;
return 1;
}
/* parse and skip a given QNAME stored in a query packet,
* from the current cursor position. returns 1 on success,
* or 0 for malformed data.
*/
static int _dnsPacket_checkQName(DnsPacket* packet) {
const uint8_t* p = packet->cursor;
const uint8_t* end = packet->end;
for (;;) {
int c;
if (p >= end) break;
c = *p++;
if (c == 0) {
packet->cursor = p;
return 1;
}
/* we don't expect label compression in QNAMEs */
if (c >= 64) break;
p += c;
/* we rely on the bound check at the start
* of the loop here */
}
/* malformed data */
LOG(INFO) << __func__ << ": malformed QNAME";
return 0;
}
/* parse and skip a given QR stored in a packet.
* returns 1 on success, and 0 on failure
*/
static int _dnsPacket_checkQR(DnsPacket* packet) {
if (!_dnsPacket_checkQName(packet)) return 0;
/* TYPE must be one of the things we support */
if (!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_A) &&
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_PTR) &&
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_MX) &&
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_AAAA) &&
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_ALL)) {
LOG(INFO) << __func__ << ": unsupported TYPE";
return 0;
}
/* CLASS must be IN */
if (!_dnsPacket_checkBytes(packet, 2, DNS_CLASS_IN)) {
LOG(INFO) << __func__ << ": unsupported CLASS";
return 0;
}
return 1;
}
/* check the header of a DNS Query packet, return 1 if it is one
* type of query we can cache, or 0 otherwise
*/
static int _dnsPacket_checkQuery(DnsPacket* packet) {
const uint8_t* p = packet->base;
int qdCount, anCount, dnCount, arCount;
if (p + DNS_HEADER_SIZE > packet->end) {
LOG(INFO) << __func__ << ": query packet too small";
return 0;
}
/* QR must be set to 0, opcode must be 0 and AA must be 0 */
/* RA, Z, and RCODE must be 0 */
if ((p[2] & 0xFC) != 0 || (p[3] & 0xCF) != 0) {
LOG(INFO) << __func__ << ": query packet flags unsupported";
return 0;
}
/* Note that we ignore the TC, RD, CD, and AD bits here for the
* following reasons:
*
* - there is no point for a query packet sent to a server
* to have the TC bit set, but the implementation might
* set the bit in the query buffer for its own needs
* between a resolv_cache_lookup and a resolv_cache_add.
* We should not freak out if this is the case.
*
* - we consider that the result from a query might depend on
* the RD, AD, and CD bits, so these bits
* should be used to differentiate cached result.
*
* this implies that these bits are checked when hashing or
* comparing query packets, but not TC
*/
/* ANCOUNT, DNCOUNT and ARCOUNT must be 0 */
qdCount = (p[4] << 8) | p[5];
anCount = (p[6] << 8) | p[7];
dnCount = (p[8] << 8) | p[9];
arCount = (p[10] << 8) | p[11];
if (anCount != 0 || dnCount != 0 || arCount > 1) {
LOG(INFO) << __func__ << ": query packet contains non-query records";
return 0;
}
if (qdCount == 0) {
LOG(INFO) << __func__ << ": query packet doesn't contain query record";
return 0;
}
/* Check QDCOUNT QRs */
packet->cursor = p + DNS_HEADER_SIZE;
for (; qdCount > 0; qdCount--)
if (!_dnsPacket_checkQR(packet)) return 0;
return 1;
}
/** QUERY DEBUGGING **/
static char* dnsPacket_bprintQName(DnsPacket* packet, char* bp, char* bend) {
const uint8_t* p = packet->cursor;
const uint8_t* end = packet->end;
int first = 1;
for (;;) {
int c;
if (p >= end) break;
c = *p++;
if (c == 0) {
packet->cursor = p;
return bp;
}
/* we don't expect label compression in QNAMEs */
if (c >= 64) break;
if (first)
first = 0;
else
bp = bprint_c(bp, bend, '.');
bp = bprint_b(bp, bend, (const char*) p, c);
p += c;
/* we rely on the bound check at the start
* of the loop here */
}
/* malformed data */
bp = bprint_s(bp, bend, "<MALFORMED>");
return bp;
}
static char* dnsPacket_bprintQR(DnsPacket* packet, char* p, char* end) {
#define QQ(x) \
{ DNS_TYPE_##x, #x }
static const struct {
const char* typeBytes;
const char* typeString;
} qTypes[] = {QQ(A), QQ(PTR), QQ(MX), QQ(AAAA), QQ(ALL), {NULL, NULL}};
int nn;
const char* typeString = NULL;
/* dump QNAME */
p = dnsPacket_bprintQName(packet, p, end);
/* dump TYPE */
p = bprint_s(p, end, " (");
for (nn = 0; qTypes[nn].typeBytes != NULL; nn++) {
if (_dnsPacket_checkBytes(packet, 2, qTypes[nn].typeBytes)) {
typeString = qTypes[nn].typeString;
break;
}
}
if (typeString != NULL)
p = bprint_s(p, end, typeString);
else {
int typeCode = _dnsPacket_readInt16(packet);
p = bprint(p, end, "UNKNOWN-%d", typeCode);
}
p = bprint_c(p, end, ')');
/* skip CLASS */
_dnsPacket_skip(packet, 2);
return p;
}
/* this function assumes the packet has already been checked */
static char* dnsPacket_bprintQuery(DnsPacket* packet, char* p, char* end) {
int qdCount;
if (packet->base[2] & 0x1) {
p = bprint_s(p, end, "RECURSIVE ");
}
_dnsPacket_skip(packet, 4);
qdCount = _dnsPacket_readInt16(packet);
_dnsPacket_skip(packet, 6);
for (; qdCount > 0; qdCount--) {
p = dnsPacket_bprintQR(packet, p, end);
}
return p;
}
/** QUERY HASHING SUPPORT
**
** THE FOLLOWING CODE ASSUMES THAT THE INPUT PACKET HAS ALREADY
** BEEN SUCCESFULLY CHECKED.
**/
/* use 32-bit FNV hash function */
#define FNV_MULT 16777619U
#define FNV_BASIS 2166136261U
static unsigned _dnsPacket_hashBytes(DnsPacket* packet, int numBytes, unsigned hash) {
const uint8_t* p = packet->cursor;
const uint8_t* end = packet->end;
while (numBytes > 0 && p < end) {
hash = hash * FNV_MULT ^ *p++;
}
packet->cursor = p;
return hash;
}
static unsigned _dnsPacket_hashQName(DnsPacket* packet, unsigned hash) {
const uint8_t* p = packet->cursor;
const uint8_t* end = packet->end;
for (;;) {
int c;
if (p >= end) { /* should not happen */
LOG(INFO) << __func__ << ": INTERNAL_ERROR: read-overflow";
break;
}
c = *p++;
if (c == 0) break;
if (c >= 64) {
LOG(INFO) << __func__ << ": INTERNAL_ERROR: malformed domain";
break;
}
if (p + c >= end) {
LOG(INFO) << __func__ << ": INTERNAL_ERROR: simple label read-overflow";
break;
}
while (c > 0) {
hash = hash * FNV_MULT ^ *p++;
c -= 1;
}
}
packet->cursor = p;
return hash;
}
static unsigned _dnsPacket_hashQR(DnsPacket* packet, unsigned hash) {
hash = _dnsPacket_hashQName(packet, hash);
hash = _dnsPacket_hashBytes(packet, 4, hash); /* TYPE and CLASS */
return hash;
}
static unsigned _dnsPacket_hashRR(DnsPacket* packet, unsigned hash) {
int rdlength;
hash = _dnsPacket_hashQR(packet, hash);
hash = _dnsPacket_hashBytes(packet, 4, hash); /* TTL */
rdlength = _dnsPacket_readInt16(packet);
hash = _dnsPacket_hashBytes(packet, rdlength, hash); /* RDATA */
return hash;
}
static unsigned _dnsPacket_hashQuery(DnsPacket* packet) {
unsigned hash = FNV_BASIS;
int count, arcount;
_dnsPacket_rewind(packet);
/* ignore the ID */
_dnsPacket_skip(packet, 2);
/* we ignore the TC bit for reasons explained in
* _dnsPacket_checkQuery().
*
* however we hash the RD bit to differentiate
* between answers for recursive and non-recursive
* queries.
*/
hash = hash * FNV_MULT ^ (packet->base[2] & 1);
/* mark the first header byte as processed */
_dnsPacket_skip(packet, 1);
/* process the second header byte */
hash = _dnsPacket_hashBytes(packet, 1, hash);
/* read QDCOUNT */
count = _dnsPacket_readInt16(packet);
/* assume: ANcount and NScount are 0 */
_dnsPacket_skip(packet, 4);
/* read ARCOUNT */
arcount = _dnsPacket_readInt16(packet);
/* hash QDCOUNT QRs */
for (; count > 0; count--) hash = _dnsPacket_hashQR(packet, hash);
/* hash ARCOUNT RRs */
for (; arcount > 0; arcount--) hash = _dnsPacket_hashRR(packet, hash);
return hash;
}
/** QUERY COMPARISON
**
** THE FOLLOWING CODE ASSUMES THAT THE INPUT PACKETS HAVE ALREADY
** BEEN SUCCESSFULLY CHECKED.
**/
static int _dnsPacket_isEqualDomainName(DnsPacket* pack1, DnsPacket* pack2) {
const uint8_t* p1 = pack1->cursor;
const uint8_t* end1 = pack1->end;
const uint8_t* p2 = pack2->cursor;
const uint8_t* end2 = pack2->end;
for (;;) {
int c1, c2;
if (p1 >= end1 || p2 >= end2) {
LOG(INFO) << __func__ << ": INTERNAL_ERROR: read-overflow";
break;
}
c1 = *p1++;
c2 = *p2++;
if (c1 != c2) break;
if (c1 == 0) {
pack1->cursor = p1;
pack2->cursor = p2;
return 1;
}
if (c1 >= 64) {
LOG(INFO) << __func__ << ": INTERNAL_ERROR: malformed domain";
break;
}
if ((p1 + c1 > end1) || (p2 + c1 > end2)) {
LOG(INFO) << __func__ << ": INTERNAL_ERROR: simple label read-overflow";
break;
}
if (memcmp(p1, p2, c1) != 0) break;
p1 += c1;
p2 += c1;
/* we rely on the bound checks at the start of the loop */
}
/* not the same, or one is malformed */
LOG(INFO) << __func__ << ": different DN";
return 0;
}
static int _dnsPacket_isEqualBytes(DnsPacket* pack1, DnsPacket* pack2, int numBytes) {
const uint8_t* p1 = pack1->cursor;
const uint8_t* p2 = pack2->cursor;
if (p1 + numBytes > pack1->end || p2 + numBytes > pack2->end) return 0;
if (memcmp(p1, p2, numBytes) != 0) return 0;
pack1->cursor += numBytes;
pack2->cursor += numBytes;
return 1;
}
static int _dnsPacket_isEqualQR(DnsPacket* pack1, DnsPacket* pack2) {
/* compare domain name encoding + TYPE + CLASS */
if (!_dnsPacket_isEqualDomainName(pack1, pack2) ||
!_dnsPacket_isEqualBytes(pack1, pack2, 2 + 2))
return 0;
return 1;
}
static int _dnsPacket_isEqualRR(DnsPacket* pack1, DnsPacket* pack2) {
int rdlength1, rdlength2;
/* compare query + TTL */
if (!_dnsPacket_isEqualQR(pack1, pack2) || !_dnsPacket_isEqualBytes(pack1, pack2, 4)) return 0;
/* compare RDATA */
rdlength1 = _dnsPacket_readInt16(pack1);
rdlength2 = _dnsPacket_readInt16(pack2);
if (rdlength1 != rdlength2 || !_dnsPacket_isEqualBytes(pack1, pack2, rdlength1)) return 0;
return 1;
}
static int _dnsPacket_isEqualQuery(DnsPacket* pack1, DnsPacket* pack2) {
int count1, count2, arcount1, arcount2;
/* compare the headers, ignore most fields */
_dnsPacket_rewind(pack1);
_dnsPacket_rewind(pack2);
/* compare RD, ignore TC, see comment in _dnsPacket_checkQuery */
if ((pack1->base[2] & 1) != (pack2->base[2] & 1)) {
LOG(INFO) << __func__ << ": different RD";
return 0;
}
if (pack1->base[3] != pack2->base[3]) {
LOG(INFO) << __func__ << ": different CD or AD";
return 0;
}
/* mark ID and header bytes as compared */
_dnsPacket_skip(pack1, 4);
_dnsPacket_skip(pack2, 4);
/* compare QDCOUNT */
count1 = _dnsPacket_readInt16(pack1);
count2 = _dnsPacket_readInt16(pack2);
if (count1 != count2 || count1 < 0) {
LOG(INFO) << __func__ << ": different QDCOUNT";
return 0;
}
/* assume: ANcount and NScount are 0 */
_dnsPacket_skip(pack1, 4);
_dnsPacket_skip(pack2, 4);
/* compare ARCOUNT */
arcount1 = _dnsPacket_readInt16(pack1);
arcount2 = _dnsPacket_readInt16(pack2);
if (arcount1 != arcount2 || arcount1 < 0) {
LOG(INFO) << __func__ << ": different ARCOUNT";
return 0;
}
/* compare the QDCOUNT QRs */
for (; count1 > 0; count1--) {
if (!_dnsPacket_isEqualQR(pack1, pack2)) {
LOG(INFO) << __func__ << ": different QR";
return 0;
}
}
/* compare the ARCOUNT RRs */
for (; arcount1 > 0; arcount1--) {
if (!_dnsPacket_isEqualRR(pack1, pack2)) {
LOG(INFO) << __func__ << ": different additional RR";
return 0;
}
}
return 1;
}
/* cache entry. for simplicity, 'hash' and 'hlink' are inlined in this
* structure though they are conceptually part of the hash table.
*
* similarly, mru_next and mru_prev are part of the global MRU list
*/
typedef struct Entry {
unsigned int hash; /* hash value */
struct Entry* hlink; /* next in collision chain */
struct Entry* mru_prev;
struct Entry* mru_next;
const uint8_t* query;
int querylen;
const uint8_t* answer;
int answerlen;
time_t expires; /* time_t when the entry isn't valid any more */
int id; /* for debugging purpose */
} Entry;
/*
* Find the TTL for a negative DNS result. This is defined as the minimum
* of the SOA records TTL and the MINIMUM-TTL field (RFC-2308).
*
* Return 0 if not found.
*/
static u_long answer_getNegativeTTL(ns_msg handle) {
int n, nscount;
u_long result = 0;
ns_rr rr;
nscount = ns_msg_count(handle, ns_s_ns);
for (n = 0; n < nscount; n++) {
if ((ns_parserr(&handle, ns_s_ns, n, &rr) == 0) && (ns_rr_type(rr) == ns_t_soa)) {
const u_char* rdata = ns_rr_rdata(rr); // find the data
const u_char* edata = rdata + ns_rr_rdlen(rr); // add the len to find the end
int len;
u_long ttl, rec_result = ns_rr_ttl(rr);
// find the MINIMUM-TTL field from the blob of binary data for this record
// skip the server name
len = dn_skipname(rdata, edata);
if (len == -1) continue; // error skipping
rdata += len;
// skip the admin name
len = dn_skipname(rdata, edata);
if (len == -1) continue; // error skipping
rdata += len;
if (edata - rdata != 5 * NS_INT32SZ) continue;
// skip: serial number + refresh interval + retry interval + expiry
rdata += NS_INT32SZ * 4;
// finally read the MINIMUM TTL
ttl = ntohl(*reinterpret_cast<const uint32_t*>(rdata));
if (ttl < rec_result) {
rec_result = ttl;
}
// Now that the record is read successfully, apply the new min TTL
if (n == 0 || rec_result < result) {
result = rec_result;
}
}
}
return result;
}
/*
* Parse the answer records and find the appropriate
* smallest TTL among the records. This might be from
* the answer records if found or from the SOA record
* if it's a negative result.
*
* The returned TTL is the number of seconds to
* keep the answer in the cache.
*
* In case of parse error zero (0) is returned which
* indicates that the answer shall not be cached.
*/
static u_long answer_getTTL(const void* answer, int answerlen) {
ns_msg handle;
int ancount, n;
u_long result, ttl;
ns_rr rr;
result = 0;
if (ns_initparse((const uint8_t*) answer, answerlen, &handle) >= 0) {
// get number of answer records
ancount = ns_msg_count(handle, ns_s_an);
if (ancount == 0) {
// a response with no answers? Cache this negative result.
result = answer_getNegativeTTL(handle);
} else {
for (n = 0; n < ancount; n++) {
if (ns_parserr(&handle, ns_s_an, n, &rr) == 0) {
ttl = ns_rr_ttl(rr);
if (n == 0 || ttl < result) {
result = ttl;
}
} else {
PLOG(INFO) << __func__ << ": ns_parserr failed ancount no = " << n;
}
}
}
} else {
PLOG(INFO) << __func__ << ": ns_initparse failed";
}
LOG(INFO) << __func__ << ": TTL = " << result;
return result;
}
static void entry_free(Entry* e) {
/* everything is allocated in a single memory block */
if (e) {
free(e);
}
}
static void entry_mru_remove(Entry* e) {
e->mru_prev->mru_next = e->mru_next;
e->mru_next->mru_prev = e->mru_prev;
}
static void entry_mru_add(Entry* e, Entry* list) {
Entry* first = list->mru_next;
e->mru_next = first;
e->mru_prev = list;
list->mru_next = e;
first->mru_prev = e;
}
/* compute the hash of a given entry, this is a hash of most
* data in the query (key) */
static unsigned entry_hash(const Entry* e) {
DnsPacket pack[1];
_dnsPacket_init(pack, e->query, e->querylen);
return _dnsPacket_hashQuery(pack);
}
/* initialize an Entry as a search key, this also checks the input query packet
* returns 1 on success, or 0 in case of unsupported/malformed data */
static int entry_init_key(Entry* e, const void* query, int querylen) {
DnsPacket pack[1];
memset(e, 0, sizeof(*e));
e->query = (const uint8_t*) query;
e->querylen = querylen;
e->hash = entry_hash(e);
_dnsPacket_init(pack, e->query, e->querylen);
return _dnsPacket_checkQuery(pack);
}
/* allocate a new entry as a cache node */
static Entry* entry_alloc(const Entry* init, const void* answer, int answerlen) {
Entry* e;
int size;
size = sizeof(*e) + init->querylen + answerlen;
e = (Entry*) calloc(size, 1);
if (e == NULL) return e;
e->hash = init->hash;
e->query = (const uint8_t*) (e + 1);
e->querylen = init->querylen;
memcpy((char*) e->query, init->query, e->querylen);
e->answer = e->query + e->querylen;
e->answerlen = answerlen;
memcpy((char*) e->answer, answer, e->answerlen);
return e;
}
static int entry_equals(const Entry* e1, const Entry* e2) {
DnsPacket pack1[1], pack2[1];
if (e1->querylen != e2->querylen) {
return 0;
}
_dnsPacket_init(pack1, e1->query, e1->querylen);
_dnsPacket_init(pack2, e2->query, e2->querylen);
return _dnsPacket_isEqualQuery(pack1, pack2);
}
/* We use a simple hash table with external collision lists
* for simplicity, the hash-table fields 'hash' and 'hlink' are
* inlined in the Entry structure.
*/
/* Maximum time for a thread to wait for an pending request */
constexpr int PENDING_REQUEST_TIMEOUT = 20;
typedef struct resolv_cache {
int max_entries;
int num_entries;
Entry mru_list;
int last_id;
Entry* entries;
struct pending_req_info {
unsigned int hash;
struct pending_req_info* next;
} pending_requests;
} Cache;
struct resolv_cache_info {
unsigned netid;
Cache* cache;
struct resolv_cache_info* next;
int nscount;
std::vector<std::string> nameservers;
struct addrinfo* nsaddrinfo[MAXNS]; // TODO: Use struct sockaddr_storage.
int revision_id; // # times the nameservers have been replaced
res_params params;
struct res_stats nsstats[MAXNS];
std::vector<std::string> search_domains;
int wait_for_pending_req_timeout_count;
// Map format: ReturnCode:rate_denom
std::unordered_map<int, uint32_t> dns_event_subsampling_map;
};
// A helper class for the Clang Thread Safety Analysis to deal with
// std::unique_lock.
class SCOPED_CAPABILITY ScopedAssumeLocked {
public:
ScopedAssumeLocked(std::mutex& mutex) ACQUIRE(mutex) {}
~ScopedAssumeLocked() RELEASE() {}
};
// lock protecting everything in the resolve_cache_info structs (next ptr, etc)
static std::mutex cache_mutex;
static std::condition_variable cv;
/* gets cache associated with a network, or NULL if none exists */
static resolv_cache* find_named_cache_locked(unsigned netid) REQUIRES(cache_mutex);
static int resolv_create_cache_for_net_locked(unsigned netid) REQUIRES(cache_mutex);
static void cache_flush_pending_requests_locked(struct resolv_cache* cache) {
resolv_cache::pending_req_info *ri, *tmp;
if (!cache) return;
ri = cache->pending_requests.next;
while (ri) {
tmp = ri;
ri = ri->next;
free(tmp);
}
cache->pending_requests.next = NULL;
cv.notify_all();
}
// Return true - if there is a pending request in |cache| matching |key|.
// Return false - if no pending request is found matching the key. Optionally
// link a new one if parameter append_if_not_found is true.
static bool cache_has_pending_request_locked(resolv_cache* cache, const Entry* key,
bool append_if_not_found) {
if (!cache || !key) return false;
resolv_cache::pending_req_info* ri = cache->pending_requests.next;
resolv_cache::pending_req_info* prev = &cache->pending_requests;
while (ri) {
if (ri->hash == key->hash) {
return true;
}
prev = ri;
ri = ri->next;
}
if (append_if_not_found) {
ri = (resolv_cache::pending_req_info*)calloc(1, sizeof(resolv_cache::pending_req_info));
if (ri) {
ri->hash = key->hash;
prev->next = ri;
}
}
return false;
}
// Notify all threads that the cache entry |key| has become available
static void _cache_notify_waiting_tid_locked(struct resolv_cache* cache, const Entry* key) {
if (!cache || !key) return;
resolv_cache::pending_req_info* ri = cache->pending_requests.next;
resolv_cache::pending_req_info* prev = &cache->pending_requests;
while (ri) {
if (ri->hash == key->hash) {
// remove item from list and destroy
prev->next = ri->next;
free(ri);
cv.notify_all();
return;
}
prev = ri;
ri = ri->next;
}
}
void _resolv_cache_query_failed(unsigned netid, const void* query, int querylen, uint32_t flags) {
// We should not notify with these flags.
if (flags & (ANDROID_RESOLV_NO_CACHE_STORE | ANDROID_RESOLV_NO_CACHE_LOOKUP)) {
return;
}
Entry key[1];
Cache* cache;
if (!entry_init_key(key, query, querylen)) return;
std::lock_guard guard(cache_mutex);
cache = find_named_cache_locked(netid);
if (cache) {
_cache_notify_waiting_tid_locked(cache, key);
}
}
static void cache_flush_locked(Cache* cache) {
int nn;
for (nn = 0; nn < cache->max_entries; nn++) {
Entry** pnode = (Entry**) &cache->entries[nn];
while (*pnode != NULL) {
Entry* node = *pnode;
*pnode = node->hlink;
entry_free(node);
}
}
// flush pending request
cache_flush_pending_requests_locked(cache);
cache->mru_list.mru_next = cache->mru_list.mru_prev = &cache->mru_list;
cache->num_entries = 0;
cache->last_id = 0;
LOG(INFO) << __func__ << ": *** DNS CACHE FLUSHED ***";
}
static resolv_cache* resolv_cache_create() {
struct resolv_cache* cache;
cache = (struct resolv_cache*) calloc(sizeof(*cache), 1);
if (cache) {
cache->max_entries = CONFIG_MAX_ENTRIES;
cache->entries = (Entry*) calloc(sizeof(*cache->entries), cache->max_entries);
if (cache->entries) {
cache->mru_list.mru_prev = cache->mru_list.mru_next = &cache->mru_list;
LOG(INFO) << __func__ << ": cache created";
} else {
free(cache);
cache = NULL;
}
}
return cache;
}
static void dump_query(const uint8_t* query, int querylen) {
if (!WOULD_LOG(VERBOSE)) return;
char temp[256], *p = temp, *end = p + sizeof(temp);
DnsPacket pack[1];
_dnsPacket_init(pack, query, querylen);
p = dnsPacket_bprintQuery(pack, p, end);
LOG(VERBOSE) << __func__ << ": " << temp;
}
static void cache_dump_mru(Cache* cache) {
char temp[512], *p = temp, *end = p + sizeof(temp);
Entry* e;
p = bprint(temp, end, "MRU LIST (%2d): ", cache->num_entries);
for (e = cache->mru_list.mru_next; e != &cache->mru_list; e = e->mru_next)
p = bprint(p, end, " %d", e->id);
LOG(INFO) << __func__ << ": " << temp;
}
/* This function tries to find a key within the hash table
* In case of success, it will return a *pointer* to the hashed key.
* In case of failure, it will return a *pointer* to NULL
*
* So, the caller must check '*result' to check for success/failure.
*
* The main idea is that the result can later be used directly in
* calls to resolv_cache_add or _resolv_cache_remove as the 'lookup'
* parameter. This makes the code simpler and avoids re-searching
* for the key position in the htable.
*
* The result of a lookup_p is only valid until you alter the hash
* table.
*/
static Entry** _cache_lookup_p(Cache* cache, Entry* key) {
int index = key->hash % cache->max_entries;
Entry** pnode = (Entry**) &cache->entries[index];
while (*pnode != NULL) {
Entry* node = *pnode;
if (node == NULL) break;
if (node->hash == key->hash && entry_equals(node, key)) break;
pnode = &node->hlink;
}
return pnode;
}
/* Add a new entry to the hash table. 'lookup' must be the
* result of an immediate previous failed _lookup_p() call
* (i.e. with *lookup == NULL), and 'e' is the pointer to the
* newly created entry
*/
static void _cache_add_p(Cache* cache, Entry** lookup, Entry* e) {
*lookup = e;
e->id = ++cache->last_id;
entry_mru_add(e, &cache->mru_list);
cache->num_entries += 1;
LOG(INFO) << __func__ << ": entry " << e->id << " added (count=" << cache->num_entries << ")";
}
/* Remove an existing entry from the hash table,
* 'lookup' must be the result of an immediate previous
* and succesful _lookup_p() call.
*/
static void _cache_remove_p(Cache* cache, Entry** lookup) {
Entry* e = *lookup;
LOG(INFO) << __func__ << ": entry " << e->id << " removed (count=" << cache->num_entries - 1
<< ")";
entry_mru_remove(e);
*lookup = e->hlink;
entry_free(e);
cache->num_entries -= 1;
}
/* Remove the oldest entry from the hash table.
*/
static void _cache_remove_oldest(Cache* cache) {
Entry* oldest = cache->mru_list.mru_prev;
Entry** lookup = _cache_lookup_p(cache, oldest);
if (*lookup == NULL) { /* should not happen */
LOG(INFO) << __func__ << ": OLDEST NOT IN HTABLE ?";
return;
}
LOG(INFO) << __func__ << ": Cache full - removing oldest";
dump_query(oldest->query, oldest->querylen);
_cache_remove_p(cache, lookup);
}
/* Remove all expired entries from the hash table.
*/
static void _cache_remove_expired(Cache* cache) {
Entry* e;
time_t now = _time_now();
for (e = cache->mru_list.mru_next; e != &cache->mru_list;) {
// Entry is old, remove
if (now >= e->expires) {
Entry** lookup = _cache_lookup_p(cache, e);
if (*lookup == NULL) { /* should not happen */
LOG(INFO) << __func__ << ": ENTRY NOT IN HTABLE ?";
return;
}
e = e->mru_next;
_cache_remove_p(cache, lookup);
} else {
e = e->mru_next;
}
}
}
// gets a resolv_cache_info associated with a network, or NULL if not found
static resolv_cache_info* find_cache_info_locked(unsigned netid) REQUIRES(cache_mutex);
ResolvCacheStatus resolv_cache_lookup(unsigned netid, const void* query, int querylen, void* answer,
int answersize, int* answerlen, uint32_t flags) {
// Skip cache lookup, return RESOLV_CACHE_NOTFOUND directly so that it is
// possible to cache the answer of this query.
// If ANDROID_RESOLV_NO_CACHE_STORE is set, return RESOLV_CACHE_SKIP to skip possible cache
// storing.
if (flags & ANDROID_RESOLV_NO_CACHE_LOOKUP) {
return flags & ANDROID_RESOLV_NO_CACHE_STORE ? RESOLV_CACHE_SKIP : RESOLV_CACHE_NOTFOUND;
}
Entry key;
Entry** lookup;
Entry* e;
time_t now;
Cache* cache;
LOG(INFO) << __func__ << ": lookup";
dump_query((u_char*) query, querylen);
/* we don't cache malformed queries */
if (!entry_init_key(&key, query, querylen)) {
LOG(INFO) << __func__ << ": unsupported query";
return RESOLV_CACHE_UNSUPPORTED;
}
/* lookup cache */
std::unique_lock lock(cache_mutex);
ScopedAssumeLocked assume_lock(cache_mutex);
cache = find_named_cache_locked(netid);
if (cache == nullptr) {
return RESOLV_CACHE_UNSUPPORTED;
}
/* see the description of _lookup_p to understand this.
* the function always return a non-NULL pointer.
*/
lookup = _cache_lookup_p(cache, &key);
e = *lookup;
if (e == NULL) {
LOG(INFO) << __func__ << ": NOT IN CACHE";
// If it is no-cache-store mode, we won't wait for possible query.
if (flags & ANDROID_RESOLV_NO_CACHE_STORE) {
return RESOLV_CACHE_SKIP;
}
if (!cache_has_pending_request_locked(cache, &key, true)) {
return RESOLV_CACHE_NOTFOUND;
} else {
LOG(INFO) << __func__ << ": Waiting for previous request";
// wait until (1) timeout OR
// (2) cv is notified AND no pending request matching the |key|
// (cv notifier should delete pending request before sending notification.)
bool ret = cv.wait_for(lock, std::chrono::seconds(PENDING_REQUEST_TIMEOUT),
[netid, &cache, &key]() REQUIRES(cache_mutex) {
// Must update cache as it could have been deleted
cache = find_named_cache_locked(netid);
return !cache_has_pending_request_locked(cache, &key, false);
});
if (!cache) {
return RESOLV_CACHE_NOTFOUND;
}
if (ret == false) {
resolv_cache_info* info = find_cache_info_locked(netid);
if (info != NULL) {
info->wait_for_pending_req_timeout_count++;
}
}
lookup = _cache_lookup_p(cache, &key);
e = *lookup;
if (e == NULL) {
return RESOLV_CACHE_NOTFOUND;
}
}
}
now = _time_now();
/* remove stale entries here */
if (now >= e->expires) {
LOG(INFO) << __func__ << ": NOT IN CACHE (STALE ENTRY " << *lookup << "DISCARDED)";
dump_query(e->query, e->querylen);
_cache_remove_p(cache, lookup);
return RESOLV_CACHE_NOTFOUND;
}
*answerlen = e->answerlen;
if (e->answerlen > answersize) {
/* NOTE: we return UNSUPPORTED if the answer buffer is too short */
LOG(INFO) << __func__ << ": ANSWER TOO LONG";
return RESOLV_CACHE_UNSUPPORTED;
}
memcpy(answer, e->answer, e->answerlen);
/* bump up this entry to the top of the MRU list */
if (e != cache->mru_list.mru_next) {
entry_mru_remove(e);
entry_mru_add(e, &cache->mru_list);
}
LOG(INFO) << __func__ << ": FOUND IN CACHE entry=" << e;
return RESOLV_CACHE_FOUND;
}
int resolv_cache_add(unsigned netid, const void* query, int querylen, const void* answer,
int answerlen) {
Entry key[1];
Entry* e;
Entry** lookup;
u_long ttl;
Cache* cache = NULL;
/* don't assume that the query has already been cached
*/
if (!entry_init_key(key, query, querylen)) {
LOG(INFO) << __func__ << ": passed invalid query?";
return -EINVAL;
}
std::lock_guard guard(cache_mutex);
cache = find_named_cache_locked(netid);
if (cache == nullptr) {
return -ENONET;
}
LOG(INFO) << __func__ << ": query:";
dump_query((u_char*)query, querylen);
res_pquery((u_char*)answer, answerlen);
if (kDumpData) {
LOG(INFO) << __func__ << ": answer:";
dump_bytes((u_char*)answer, answerlen);
}
lookup = _cache_lookup_p(cache, key);
e = *lookup;
// Should only happen on ANDROID_RESOLV_NO_CACHE_LOOKUP
if (e != NULL) {
LOG(INFO) << __func__ << ": ALREADY IN CACHE (" << e << ") ? IGNORING ADD";
_cache_notify_waiting_tid_locked(cache, key);
return -EEXIST;
}
if (cache->num_entries >= cache->max_entries) {
_cache_remove_expired(cache);
if (cache->num_entries >= cache->max_entries) {
_cache_remove_oldest(cache);
}
// TODO: It looks useless, remove below code after having test to prove it.
lookup = _cache_lookup_p(cache, key);
e = *lookup;
if (e != NULL) {
LOG(INFO) << __func__ << ": ALREADY IN CACHE (" << e << ") ? IGNORING ADD";
_cache_notify_waiting_tid_locked(cache, key);
return -EEXIST;
}
}
ttl = answer_getTTL(answer, answerlen);
if (ttl > 0) {
e = entry_alloc(key, answer, answerlen);
if (e != NULL) {
e->expires = ttl + _time_now();
_cache_add_p(cache, lookup, e);
}
}
cache_dump_mru(cache);
_cache_notify_waiting_tid_locked(cache, key);
return 0;
}
// Head of the list of caches.
static struct resolv_cache_info res_cache_list GUARDED_BY(cache_mutex);
// insert resolv_cache_info into the list of resolv_cache_infos
static void insert_cache_info_locked(resolv_cache_info* cache_info);
// creates a resolv_cache_info
static resolv_cache_info* create_cache_info();
// empty the nameservers set for the named cache
static void free_nameservers_locked(resolv_cache_info* cache_info);
// Order-insensitive comparison for the two set of servers.
static bool resolv_is_nameservers_equal(const std::vector<std::string>& oldServers,
const std::vector<std::string>& newServers);
// clears the stats samples contained withing the given cache_info
static void res_cache_clear_stats_locked(resolv_cache_info* cache_info);
// public API for netd to query if name server is set on specific netid
bool resolv_has_nameservers(unsigned netid) {
std::lock_guard guard(cache_mutex);
resolv_cache_info* info = find_cache_info_locked(netid);
return (info != nullptr) && (info->nscount > 0);
}
namespace {
// Map format: ReturnCode:rate_denom
// if the ReturnCode is not associated with any rate_denom, use default
// Sampling rate varies by return code; events to log are chosen randomly, with a
// probability proportional to the sampling rate.
constexpr const char DEFAULT_SUBSAMPLING_MAP[] = "default:1 0:100 7:10";
std::unordered_map<int, uint32_t> resolv_get_dns_event_subsampling_map() {
using android::base::ParseInt;
using android::base::ParseUint;
using android::base::Split;
using server_configurable_flags::GetServerConfigurableFlag;
std::unordered_map<int, uint32_t> sampling_rate_map{};
std::vector<std::string> subsampling_vector =
Split(GetServerConfigurableFlag("netd_native", "dns_event_subsample_map",
DEFAULT_SUBSAMPLING_MAP),
" ");
for (const auto& pair : subsampling_vector) {
std::vector<std::string> rate_denom = Split(pair, ":");
int return_code;
uint32_t denom;
if (rate_denom.size() != 2) {
LOG(ERROR) << __func__ << ": invalid subsampling_pair = " << pair;
continue;
}
if (rate_denom[0] == "default") {
return_code = DNSEVENT_SUBSAMPLING_MAP_DEFAULT_KEY;
} else if (!ParseInt(rate_denom[0], &return_code)) {
LOG(ERROR) << __func__ << ": parse subsampling_pair failed = " << pair;
continue;
}
if (!ParseUint(rate_denom[1], &denom)) {
LOG(ERROR) << __func__ << ": parse subsampling_pair failed = " << pair;
continue;
}
sampling_rate_map[return_code] = denom;
}
return sampling_rate_map;
}
} // namespace
static int resolv_create_cache_for_net_locked(unsigned netid) {
resolv_cache* cache = find_named_cache_locked(netid);
// Should not happen
if (cache) {
LOG(ERROR) << __func__ << ": Cache is already created, netId: " << netid;
return -EEXIST;
}
resolv_cache_info* cache_info = create_cache_info();
if (!cache_info) return -ENOMEM;
cache = resolv_cache_create();
if (!cache) {
free(cache_info);
return -ENOMEM;
}
cache_info->cache = cache;
cache_info->netid = netid;
cache_info->dns_event_subsampling_map = resolv_get_dns_event_subsampling_map();
insert_cache_info_locked(cache_info);
return 0;
}
int resolv_create_cache_for_net(unsigned netid) {
std::lock_guard guard(cache_mutex);
return resolv_create_cache_for_net_locked(netid);
}
void resolv_delete_cache_for_net(unsigned netid) {
std::lock_guard guard(cache_mutex);
struct resolv_cache_info* prev_cache_info = &res_cache_list;
while (prev_cache_info->next) {
struct resolv_cache_info* cache_info = prev_cache_info->next;
if (cache_info->netid == netid) {
prev_cache_info->next = cache_info->next;
cache_flush_locked(cache_info->cache);
free(cache_info->cache->entries);
free(cache_info->cache);
free_nameservers_locked(cache_info);
free(cache_info);
break;
}
prev_cache_info = prev_cache_info->next;
}
}
std::vector<unsigned> resolv_list_caches() {
std::lock_guard guard(cache_mutex);
struct resolv_cache_info* cache_info = res_cache_list.next;
std::vector<unsigned> result;
while (cache_info) {
result.push_back(cache_info->netid);
cache_info = cache_info->next;
}
return result;
}
static resolv_cache_info* create_cache_info() {
return (struct resolv_cache_info*) calloc(sizeof(struct resolv_cache_info), 1);
}
// TODO: convert this to a simple and efficient C++ container.
static void insert_cache_info_locked(struct resolv_cache_info* cache_info) {
struct resolv_cache_info* last;
for (last = &res_cache_list; last->next; last = last->next) {}
last->next = cache_info;
}
static resolv_cache* find_named_cache_locked(unsigned netid) {
resolv_cache_info* info = find_cache_info_locked(netid);
if (info != nullptr) return info->cache;
return nullptr;
}
static resolv_cache_info* find_cache_info_locked(unsigned netid) {
struct resolv_cache_info* cache_info = res_cache_list.next;
while (cache_info) {
if (cache_info->netid == netid) {
break;
}
cache_info = cache_info->next;
}
return cache_info;
}
static void resolv_set_experiment_params(res_params* params) {
using android::base::ParseInt;
using server_configurable_flags::GetServerConfigurableFlag;
if (params->retry_count == 0) {
params->retry_count = RES_DFLRETRY;
ParseInt(GetServerConfigurableFlag("netd_native", "retry_count", ""), &params->retry_count);
}
if (params->base_timeout_msec == 0) {
params->base_timeout_msec = RES_TIMEOUT;
ParseInt(GetServerConfigurableFlag("netd_native", "retransmission_time_interval", ""),
&params->base_timeout_msec);
}
}
namespace {
// Returns valid domains without duplicates which are limited to max size |MAXDNSRCH|.
std::vector<std::string> filter_domains(const std::vector<std::string>& domains) {
std::set<std::string> tmp_set;
std::vector<std::string> res;
std::copy_if(domains.begin(), domains.end(), std::back_inserter(res),
[&tmp_set](const std::string& str) {
return !(str.size() > MAXDNSRCHPATH - 1) && (tmp_set.insert(str).second);
});
if (res.size() > MAXDNSRCH) {
LOG(WARNING) << __func__ << ": valid domains=" << res.size()
<< ", but MAXDNSRCH=" << MAXDNSRCH;
res.resize(MAXDNSRCH);
}
return res;
}
std::vector<std::string> filter_nameservers(const std::vector<std::string>& servers) {
std::vector<std::string> res = servers;
if (res.size() > MAXNS) {
LOG(WARNING) << __func__ << ": too many servers: " << res.size();
res.resize(MAXNS);
}
return res;
}
} // namespace
int resolv_set_nameservers(unsigned netid, const std::vector<std::string>& servers,
const std::vector<std::string>& domains, const res_params& params) {
std::vector<std::string> nameservers = filter_nameservers(servers);
const int numservers = static_cast<int>(nameservers.size());
LOG(INFO) << __func__ << ": netId = " << netid << ", numservers = " << numservers;
// Parse the addresses before actually locking or changing any state, in case there is an error.
// As a side effect this also reduces the time the lock is kept.
// TODO: find a better way to replace addrinfo*, something like std::vector<SafeAddrinfo>
addrinfo* nsaddrinfo[MAXNS];
for (int i = 0; i < numservers; i++) {
// The addrinfo structures allocated here are freed in free_nameservers_locked().
const addrinfo hints = {
.ai_family = AF_UNSPEC, .ai_socktype = SOCK_DGRAM, .ai_flags = AI_NUMERICHOST};
const int rt = getaddrinfo_numeric(nameservers[i].c_str(), "53", hints, &nsaddrinfo[i]);
if (rt != 0) {
for (int j = 0; j < i; j++) {
freeaddrinfo(nsaddrinfo[j]);
}
LOG(INFO) << __func__ << ": getaddrinfo_numeric(" << nameservers[i]
<< ") = " << gai_strerror(rt);
return -EINVAL;
}
}
std::lock_guard guard(cache_mutex);
resolv_cache_info* cache_info = find_cache_info_locked(netid);
if (cache_info == nullptr) return -ENONET;
uint8_t old_max_samples = cache_info->params.max_samples;
cache_info->params = params;
resolv_set_experiment_params(&cache_info->params);
if (!resolv_is_nameservers_equal(cache_info->nameservers, nameservers)) {
// free current before adding new
free_nameservers_locked(cache_info);
cache_info->nameservers = std::move(nameservers);
for (int i = 0; i < numservers; i++) {
cache_info->nsaddrinfo[i] = nsaddrinfo[i];
LOG(INFO) << __func__ << ": netid = " << netid
<< ", addr = " << cache_info->nameservers[i];
}
cache_info->nscount = numservers;
// Clear the NS statistics because the mapping to nameservers might have changed.
res_cache_clear_stats_locked(cache_info);
// increment the revision id to ensure that sample state is not written back if the
// servers change; in theory it would suffice to do so only if the servers or
// max_samples actually change, in practice the overhead of checking is higher than the
// cost, and overflows are unlikely
++cache_info->revision_id;
} else {
if (cache_info->params.max_samples != old_max_samples) {
// If the maximum number of samples changes, the overhead of keeping the most recent
// samples around is not considered worth the effort, so they are cleared instead.
// All other parameters do not affect shared state: Changing these parameters does
// not invalidate the samples, as they only affect aggregation and the conditions
// under which servers are considered usable.
res_cache_clear_stats_locked(cache_info);
++cache_info->revision_id;
}
for (int j = 0; j < numservers; j++) {
freeaddrinfo(nsaddrinfo[j]);
}
}
// Always update the search paths. Cache-flushing however is not necessary,
// since the stored cache entries do contain the domain, not just the host name.
cache_info->search_domains = filter_domains(domains);
return 0;
}
static bool resolv_is_nameservers_equal(const std::vector<std::string>& oldServers,
const std::vector<std::string>& newServers) {
const std::set<std::string> olds(oldServers.begin(), oldServers.end());
const std::set<std::string> news(newServers.begin(), newServers.end());
// TODO: this is incorrect if the list of current or previous nameservers
// contains duplicates. This does not really matter because the framework
// filters out duplicates, but we should probably fix it. It's also
// insensitive to the order of the nameservers; we should probably fix that
// too.
return olds == news;
}
static void free_nameservers_locked(resolv_cache_info* cache_info) {
int i;
for (i = 0; i < cache_info->nscount; i++) {
cache_info->nameservers.clear();
if (cache_info->nsaddrinfo[i] != NULL) {
freeaddrinfo(cache_info->nsaddrinfo[i]);
cache_info->nsaddrinfo[i] = NULL;
}
cache_info->nsstats[i].sample_count = cache_info->nsstats[i].sample_next = 0;
}
cache_info->nscount = 0;
res_cache_clear_stats_locked(cache_info);
++cache_info->revision_id;
}
void _resolv_populate_res_for_net(res_state statp) {
if (statp == NULL) {
return;
}
LOG(INFO) << __func__ << ": netid=" << statp->netid;
std::lock_guard guard(cache_mutex);
resolv_cache_info* info = find_cache_info_locked(statp->netid);
if (info != NULL) {
int nserv;
struct addrinfo* ai;
for (nserv = 0; nserv < MAXNS; nserv++) {
ai = info->nsaddrinfo[nserv];
if (ai == NULL) {
break;
}
if ((size_t) ai->ai_addrlen <= sizeof(statp->_u._ext.ext->nsaddrs[0])) {
if (statp->_u._ext.ext != NULL) {
memcpy(&statp->_u._ext.ext->nsaddrs[nserv], ai->ai_addr, ai->ai_addrlen);
statp->nsaddr_list[nserv].sin_family = AF_UNSPEC;
} else {
if ((size_t) ai->ai_addrlen <= sizeof(statp->nsaddr_list[0])) {
memcpy(&statp->nsaddr_list[nserv], ai->ai_addr, ai->ai_addrlen);
} else {
statp->nsaddr_list[nserv].sin_family = AF_UNSPEC;
}
}
} else {
LOG(INFO) << __func__ << ": found too long addrlen";
}
}
statp->nscount = nserv;
statp->search_domains = info->search_domains;
}
}
/* Resolver reachability statistics. */
static void _res_cache_add_stats_sample_locked(res_stats* stats, const res_sample* sample,
int max_samples) {
// Note: This function expects max_samples > 0, otherwise a (harmless) modification of the
// allocated but supposedly unused memory for samples[0] will happen
LOG(INFO) << __func__ << ": adding sample to stats, next = " << unsigned(stats->sample_next)
<< ", count = " << unsigned(stats->sample_count);
stats->samples[stats->sample_next] = *sample;
if (stats->sample_count < max_samples) {
++stats->sample_count;
}
if (++stats->sample_next >= max_samples) {
stats->sample_next = 0;
}
}
static void res_cache_clear_stats_locked(resolv_cache_info* cache_info) {
if (cache_info) {
for (int i = 0; i < MAXNS; ++i) {
cache_info->nsstats->sample_count = cache_info->nsstats->sample_next = 0;
}
}
}
int android_net_res_stats_get_info_for_net(unsigned netid, int* nscount,
struct sockaddr_storage servers[MAXNS], int* dcount,
char domains[MAXDNSRCH][MAXDNSRCHPATH],
res_params* params, struct res_stats stats[MAXNS],
int* wait_for_pending_req_timeout_count) {
int revision_id = -1;
std::lock_guard guard(cache_mutex);
resolv_cache_info* info = find_cache_info_locked(netid);
if (info) {
if (info->nscount > MAXNS) {
LOG(INFO) << __func__ << ": nscount " << info->nscount << " > MAXNS " << MAXNS;
errno = EFAULT;
return -1;
}
int i;
for (i = 0; i < info->nscount; i++) {
// Verify that the following assumptions are held, failure indicates corruption:
// - getaddrinfo() may never return a sockaddr > sockaddr_storage
// - all addresses are valid
// - there is only one address per addrinfo thanks to numeric resolution
int addrlen = info->nsaddrinfo[i]->ai_addrlen;
if (addrlen < (int) sizeof(struct sockaddr) || addrlen > (int) sizeof(servers[0])) {
LOG(INFO) << __func__ << ": nsaddrinfo[" << i << "].ai_addrlen == " << addrlen;
errno = EMSGSIZE;
return -1;
}
if (info->nsaddrinfo[i]->ai_addr == NULL) {
LOG(INFO) << __func__ << ": nsaddrinfo[" << i << "].ai_addr == NULL";
errno = ENOENT;
return -1;
}
if (info->nsaddrinfo[i]->ai_next != NULL) {
LOG(INFO) << __func__ << ": nsaddrinfo[" << i << "].ai_next != NULL";
errno = ENOTUNIQ;
return -1;
}
}
*nscount = info->nscount;
for (i = 0; i < info->nscount; i++) {
memcpy(&servers[i], info->nsaddrinfo[i]->ai_addr, info->nsaddrinfo[i]->ai_addrlen);
stats[i] = info->nsstats[i];
}
for (i = 0; i < static_cast<int>(info->search_domains.size()); i++) {
strlcpy(domains[i], info->search_domains[i].c_str(), MAXDNSRCHPATH);
}
*dcount = i;
*params = info->params;
revision_id = info->revision_id;
*wait_for_pending_req_timeout_count = info->wait_for_pending_req_timeout_count;
}
return revision_id;
}
std::vector<std::string> resolv_cache_dump_subsampling_map(unsigned netid) {
using android::base::StringPrintf;
std::lock_guard guard(cache_mutex);
resolv_cache_info* cache_info = find_cache_info_locked(netid);
if (cache_info == nullptr) return {};
std::vector<std::string> result;
for (const auto& pair : cache_info->dns_event_subsampling_map) {
result.push_back(StringPrintf("%s:%d",
(pair.first == DNSEVENT_SUBSAMPLING_MAP_DEFAULT_KEY)
? "default"
: std::to_string(pair.first).c_str(),
pair.second));
}
return result;
}
// Decides whether an event should be sampled using a random number generator and
// a sampling factor derived from the netid and the return code.
//
// Returns the subsampling rate if the event should be sampled, or 0 if it should be discarded.
uint32_t resolv_cache_get_subsampling_denom(unsigned netid, int return_code) {
std::lock_guard guard(cache_mutex);
resolv_cache_info* cache_info = find_cache_info_locked(netid);
if (cache_info == nullptr) return 0; // Don't log anything at all.
const auto& subsampling_map = cache_info->dns_event_subsampling_map;
auto search_returnCode = subsampling_map.find(return_code);
uint32_t denom;
if (search_returnCode != subsampling_map.end()) {
denom = search_returnCode->second;
} else {
auto search_default = subsampling_map.find(DNSEVENT_SUBSAMPLING_MAP_DEFAULT_KEY);
denom = (search_default == subsampling_map.end()) ? 0 : search_default->second;
}
return denom;
}
int resolv_cache_get_resolver_stats(unsigned netid, res_params* params, res_stats stats[MAXNS]) {
std::lock_guard guard(cache_mutex);
resolv_cache_info* info = find_cache_info_locked(netid);
if (info) {
memcpy(stats, info->nsstats, sizeof(info->nsstats));
*params = info->params;
return info->revision_id;
}
return -1;
}
void _resolv_cache_add_resolver_stats_sample(unsigned netid, int revision_id, int ns,
const res_sample* sample, int max_samples) {
if (max_samples <= 0) return;
std::lock_guard guard(cache_mutex);
resolv_cache_info* info = find_cache_info_locked(netid);
if (info && info->revision_id == revision_id) {
_res_cache_add_stats_sample_locked(&info->nsstats[ns], sample, max_samples);
}
}
bool has_named_cache(unsigned netid) {
std::lock_guard guard(cache_mutex);
return find_named_cache_locked(netid) != nullptr;
}
int resolv_cache_get_expiration(unsigned netid, const std::vector<char>& query,
time_t* expiration) {
Entry key;
*expiration = -1;
// A malformed query is not allowed.
if (!entry_init_key(&key, query.data(), query.size())) {
LOG(WARNING) << __func__ << ": unsupported query";
return -EINVAL;
}
// lookup cache.
Cache* cache;
std::lock_guard guard(cache_mutex);
if (cache = find_named_cache_locked(netid); cache == nullptr) {
LOG(WARNING) << __func__ << ": cache not created in the network " << netid;
return -ENONET;
}
Entry** lookup = _cache_lookup_p(cache, &key);
Entry* e = *lookup;
if (e == NULL) {
LOG(WARNING) << __func__ << ": not in cache";
return -ENODATA;
}
if (_time_now() >= e->expires) {
LOG(WARNING) << __func__ << ": entry expired";
return -ENODATA;
}
*expiration = e->expires;
return 0;
}