| commit | db5d47a446c9fdd48487887c4b0be9ca58961c00 | [log] [tgz] |
|---|---|---|
| author | Denis Ovsienko <denis@ovsienko.info> | Sun Jun 12 17:19:46 2022 +0100 |
| committer | Guy Harris <gharris@sonic.net> | Fri Jul 08 14:42:56 2022 -0700 |
| tree | c56fe91f87606136e92716c7cb5c0e94f1b0b43f | |
| parent | 56b722c4c2ef72cc653e979ab488383bfb0ee595 [diff] |
Expand abbreviations into "proto X" properly. Make the "ah", "esp", "pim", "sctp", "tcp" and "udp" abbreviations compile exactly the same as what they expand into (as far as pcap-filter(7) defines it). Before commit 2ae1134 gen_proto_abbrev_internal() always generated the IPv4 leg last; when IPv6 was enabled, it generated the IPv6 leg first and ORed the two together; gen_proto() always generated the IPv4 leg first; when IPv6 was enabled, it generated the IPv6 leg last and ORed the two together. This way, with IPv6 enabled "ah" and "proto \ah" produced different (although effectively equivalent) sequences of statements. After commit 2ae1134 the difference became unconditional and respective code in gen_proto_abbrev_internal() effectively duplicated the code in gen_proto(). Address that by calling the latter properly from the former, so whatever the full syntax produces in the current revision, the abbreviation always produces exactly the same. The difference made it unnecessarily convoluted to compare compiled filters when one filter used an abbreviation and the other used the full syntax. For example, without the source code and an up to date man page trying to tell whether "sctp" and "proto \sctp" have the same effect is as simple as the following: $ tcpdump -y EN10MB -d 'proto \sctp' (000) ldh [12] (001) jeq #0x800 jt 2 jf 4 (002) ldb [23] (003) jeq #0x84 jt 10 jf 11 (004) jeq #0x86dd jt 5 jf 11 (005) ldb [20] (006) jeq #0x84 jt 10 jf 7 (007) jeq #0x2c jt 8 jf 11 (008) ldb [54] (009) jeq #0x84 jt 10 jf 11 (010) ret #262144 (011) ret #0 $ tcpdump -y EN10MB -d 'sctp' # before this change (000) ldh [12] (001) jeq #0x86dd jt 2 jf 7 (002) ldb [20] (003) jeq #0x84 jt 10 jf 4 (004) jeq #0x2c jt 5 jf 11 (005) ldb [54] (006) jeq #0x84 jt 10 jf 11 (007) jeq #0x800 jt 8 jf 11 (008) ldb [23] (009) jeq #0x84 jt 10 jf 11 (010) ret #262144 (011) ret #0 $ tcpdump -y EN10MB -d 'sctp' # after this change (000) ldh [12] (001) jeq #0x800 jt 2 jf 4 (002) ldb [23] (003) jeq #0x84 jt 10 jf 11 (004) jeq #0x86dd jt 5 jf 11 (005) ldb [20] (006) jeq #0x84 jt 10 jf 7 (007) jeq #0x2c jt 8 jf 11 (008) ldb [54] (009) jeq #0x84 jt 10 jf 11 (010) ret #262144 (011) ret #0 (cherry picked from commit c93c8ff003091f78c2bc70422d71a68bf95e5bde)
To report a security issue please send an e-mail to security@tcpdump.org.
To report bugs and other problems, contribute patches, request a feature, provide generic feedback etc please see the guidelines for contributing.
The documentation directory has README files about specific operating systems and options.
Anonymous Git is available via:
https://github.com/the-tcpdump-group/libpcap.git
This directory contains source code for libpcap, a system-independent interface for user-level packet capture. libpcap provides a portable framework for low-level network monitoring. Applications include network statistics collection, security monitoring, network debugging, etc. Since almost every system vendor provides a different interface for packet capture, and since we‘ve developed several tools that require this functionality, we’ve created this system-independent API to ease in porting and to alleviate the need for several system-dependent packet capture modules in each application.
formerly from Lawrence Berkeley National Laboratory Network Research Group <libpcap@ee.lbl.gov> ftp://ftp.ee.lbl.gov/old/libpcap-0.4a7.tar.Z
For some platforms there are README.{system} files that discuss issues with the OS‘s interface for packet capture on those platforms, such as how to enable support for that interface in the OS, if it’s not built in by default.
The libpcap interface supports a filtering mechanism based on the architecture in the BSD packet filter. BPF is described in the 1993 Winter Usenix paper ``The BSD Packet Filter: A New Architecture for User-level Packet Capture'' (compressed PostScript, gzipped PostScript, PDF).
Although most packet capture interfaces support in-kernel filtering, libpcap utilizes in-kernel filtering only for the BPF interface. On systems that don't have BPF, all packets are read into user-space and the BPF filters are evaluated in the libpcap library, incurring added overhead (especially, for selective filters). Ideally, libpcap would translate BPF filters into a filter program that is compatible with the underlying kernel subsystem, but this is not yet implemented.
BPF is standard in 4.4BSD, BSD/OS, NetBSD, FreeBSD, OpenBSD, DragonFly BSD, macOS, and Solaris 11; an older, modified and undocumented version is standard in AIX. {DEC OSF/1, Digital UNIX, Tru64 UNIX} uses the packetfilter interface but has been extended to accept BPF filters (which libpcap utilizes). Also, you can add BPF filter support to Ultrix using the kernel source and/or object patches available here.
Linux has a number of BPF based systems, and libpcap does not support any of the eBPF mechanisms as yet, although it supports many of the memory mapped receive mechanisms. See the Linux-specific README for more information.
There's now a rule to make a shared library, which should work on Linux and *BSD, among other platforms.
It sets the soname of the library to libpcap.so.1; this is what it should be, NOT libpcap.so.1.x or libpcap.so.1.x.y or something such as that.
We‘ve been maintaining binary compatibility between libpcap releases for quite a while; there’s no reason to tie a binary linked with libpcap to a particular release of libpcap.