UPSTREAM: iptables: insist that the lock is held.
Currently, iptables programs will exit with an error if the
iptables lock cannot be acquired, but will silently continue if
the lock cannot be opened at all. This can cause unexpected
failures (with unhelpful error messages) in the presence of
concurrent updates, which can be very difficult to find in a
complex or multi-administrator system.
Instead, refuse to do anything if the lock cannot be acquired.
The behaviour is not affected by command-line flags because:
1. In order to reliably avoid concurrent modification, all
invocations of iptables commands must follow this behaviour.
2. Whether or not the lock can be opened is typically not
a run-time condition but is likely to be a configuration
error.
Existing systems that depended on things working mostly correctly
even if there was no lock might be affected by this change.
However, that is arguably a configuration error, and now that the
iptables lock is configurable, it is trivial to provide a lock
file that is always accessible: if nothing else, the iptables
binary itself can be used. The lock does not have to be writable,
only readable.
Tested by configuring the system to use an xtables.lock file in
a non-existent directory and observing that all commands failed.
(cherry picked from iptables 80d8bfaac9e2430d710084a10ec78e68bd61e6ec)
Test: aosp_bullhead-eng builds
Change-Id: I1aec4eb2d9e3775806c93ccd6cf215af05e12f3c
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/iptables/ip6tables-restore.c b/iptables/ip6tables-restore.c
index 7d40590..0db8d84 100644
--- a/iptables/ip6tables-restore.c
+++ b/iptables/ip6tables-restore.c
@@ -296,12 +296,7 @@
in_table = 0;
} else if ((buffer[0] == '*') && (!in_table)) {
/* Acquire a lock before we create a new table handle */
- lock = xtables_lock(wait, &wait_interval);
- if (lock == XT_LOCK_BUSY) {
- fprintf(stderr, "Another app is currently holding the xtables lock. "
- "Perhaps you want to use the -w option?\n");
- exit(RESOURCE_PROBLEM);
- }
+ lock = xtables_lock_or_exit(wait, &wait_interval);
/* New table */
char *table;
diff --git a/iptables/ip6tables.c b/iptables/ip6tables.c
index 579d347..49bd006 100644
--- a/iptables/ip6tables.c
+++ b/iptables/ip6tables.c
@@ -1779,15 +1779,8 @@
generic_opt_check(command, cs.options);
/* Attempt to acquire the xtables lock */
- if (!restore && xtables_lock(wait, &wait_interval) == XT_LOCK_BUSY) {
- fprintf(stderr, "Another app is currently holding the xtables lock. ");
- if (wait == 0)
- fprintf(stderr, "Perhaps you want to use the -w option?\n");
- else
- fprintf(stderr, "Stopped waiting after %ds.\n", wait);
- xtables_free_opts(1);
- exit(RESOURCE_PROBLEM);
- }
+ if (!restore)
+ xtables_lock_or_exit(wait, &wait_interval);
/* only allocate handle if we weren't called with a handle */
if (!*handle)
diff --git a/iptables/iptables-restore.c b/iptables/iptables-restore.c
index 113045d..078d1d4 100644
--- a/iptables/iptables-restore.c
+++ b/iptables/iptables-restore.c
@@ -295,12 +295,7 @@
in_table = 0;
} else if ((buffer[0] == '*') && (!in_table)) {
/* Acquire a lock before we create a new table handle */
- lock = xtables_lock(wait, &wait_interval);
- if (lock == XT_LOCK_BUSY) {
- fprintf(stderr, "Another app is currently holding the xtables lock. "
- "Perhaps you want to use the -w option?\n");
- exit(RESOURCE_PROBLEM);
- }
+ lock = xtables_lock_or_exit(wait, &wait_interval);
/* New table */
char *table;
diff --git a/iptables/iptables.c b/iptables/iptables.c
index 62731c5..d61d5b9 100644
--- a/iptables/iptables.c
+++ b/iptables/iptables.c
@@ -1766,15 +1766,8 @@
generic_opt_check(command, cs.options);
/* Attempt to acquire the xtables lock */
- if (!restore && xtables_lock(wait, &wait_interval) == XT_LOCK_BUSY) {
- fprintf(stderr, "Another app is currently holding the xtables lock. ");
- if (wait == 0)
- fprintf(stderr, "Perhaps you want to use the -w option?\n");
- else
- fprintf(stderr, "Stopped waiting after %ds.\n", wait);
- xtables_free_opts(1);
- exit(RESOURCE_PROBLEM);
- }
+ if (!restore)
+ xtables_lock_or_exit(wait, &wait_interval);
/* only allocate handle if we weren't called with a handle */
if (!*handle)
diff --git a/iptables/xshared.c b/iptables/xshared.c
index 3fbe3b1..825479c 100644
--- a/iptables/xshared.c
+++ b/iptables/xshared.c
@@ -246,7 +246,7 @@
match->init(match->m);
}
-int xtables_lock(int wait, struct timeval *wait_interval)
+static int xtables_lock(int wait, struct timeval *wait_interval)
{
struct timeval time_left, wait_time;
int fd, i = 0;
@@ -255,8 +255,11 @@
time_left.tv_usec = 0;
fd = open(XT_LOCK_NAME, O_CREAT, 0600);
- if (fd < 0)
- return XT_LOCK_UNSUPPORTED;
+ if (fd < 0) {
+ fprintf(stderr, "Fatal: can't open lock file %s: %s\n",
+ XT_LOCK_NAME, strerror(errno));
+ return XT_LOCK_FAILED;
+ }
if (wait == -1) {
if (flock(fd, LOCK_EX) == 0)
@@ -291,6 +294,28 @@
close(lock);
}
+int xtables_lock_or_exit(int wait, struct timeval *wait_interval)
+{
+ int lock = xtables_lock(wait, wait_interval);
+
+ if (lock == XT_LOCK_FAILED) {
+ xtables_free_opts(1);
+ exit(RESOURCE_PROBLEM);
+ }
+
+ if (lock == XT_LOCK_BUSY) {
+ fprintf(stderr, "Another app is currently holding the xtables lock. ");
+ if (wait == 0)
+ fprintf(stderr, "Perhaps you want to use the -w option?\n");
+ else
+ fprintf(stderr, "Stopped waiting after %ds.\n", wait);
+ xtables_free_opts(1);
+ exit(RESOURCE_PROBLEM);
+ }
+
+ return lock;
+}
+
int parse_wait_time(int argc, char *argv[])
{
int wait = -1;
diff --git a/iptables/xshared.h b/iptables/xshared.h
index f8dc527..e390f64 100644
--- a/iptables/xshared.h
+++ b/iptables/xshared.h
@@ -93,8 +93,7 @@
*
* A value >= 0 indicates the lock filedescriptor. Other values are:
*
- * XT_LOCK_UNSUPPORTED : The system does not support locking, execution will
- * proceed lockless.
+ * XT_LOCK_FAILED : The lock could not be acquired.
*
* XT_LOCK_BUSY : The lock was held by another process. xtables_lock only
* returns this value when |wait| == false. If |wait| == true, xtables_lock
@@ -104,11 +103,11 @@
*/
enum {
XT_LOCK_BUSY = -1,
- XT_LOCK_UNSUPPORTED = -2,
+ XT_LOCK_FAILED = -2,
XT_LOCK_NOT_ACQUIRED = -3,
};
-extern int xtables_lock(int wait, struct timeval *tv);
extern void xtables_unlock(int lock);
+extern int xtables_lock_or_exit(int wait, struct timeval *tv);
int parse_wait_time(int argc, char *argv[]);
void parse_wait_interval(int argc, char *argv[], struct timeval *wait_interval);
