171 lines
7.2 KiB
Plaintext
171 lines
7.2 KiB
Plaintext
Some Information for Contributors
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---------------------------------
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Thank you for considering to make a contribution to tcpdump! Please use the
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guidelines below to achieve the best results and experience for everyone.
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How to report bugs and other problems
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-------------------------------------
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To report a security issue (segfault, buffer overflow, infinite loop, arbitrary
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code execution etc) please send an e-mail to security@tcpdump.org, do not use
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the bug tracker!
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To report a non-security problem (failure to compile, incorrect output in the
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protocol printout, missing support for a particular protocol etc) please check
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first that it reproduces with the latest stable release of tcpdump and the latest
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stable release of libpcap. If it does, please check that the problem reproduces
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with the current git master branch of tcpdump and the current git master branch of
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libpcap. If it does (and it is not a security-related problem, otherwise see
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above), please navigate to https://github.com/the-tcpdump-group/tcpdump/issues
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and check if the problem has already been reported. If it has not, please open
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a new issue and provide the following details:
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* tcpdump and libpcap version (tcpdump --version)
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* operating system name and version and any other details that may be relevant
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(uname -a, compiler name and version, CPU type etc.)
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* custom configure/CMake flags, if any
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* statement of the problem
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* steps to reproduce
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Please note that if you know exactly how to solve the problem and the solution
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would not be too intrusive, it would be best to contribute some development time
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and to open a pull request instead as discussed below.
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Still not sure how to do? Feel free to [subscribe](https://www.tcpdump.org/#mailing-lists)
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to the mailing list tcpdump-workers@lists.tcpdump.org and ask!
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How to add new code and to update existing code
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-----------------------------------------------
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0) Check that there isn't a pull request already opened for the changes you
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intend to make.
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1) Fork the Tcpdump repository on GitHub from
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https://github.com/the-tcpdump-group/tcpdump
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(See https://help.github.com/articles/fork-a-repo/)
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2) The easiest way to test your changes on multiple operating systems and
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architectures is to let the upstream CI test your pull request (more on
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this below).
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3) Setup your git working copy
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git clone https://github.com/<username>/tcpdump.git
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cd tcpdump
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git remote add upstream https://github.com/the-tcpdump-group/tcpdump
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git fetch upstream
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4) Do a 'touch .devel' in your working directory.
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Currently, the effect is
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a) add (via configure, in Makefile) some warnings options ( -Wall
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-Wmissing-prototypes -Wstrict-prototypes, ...) to the compiler if it
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supports these options,
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b) have the Makefile support "make depend" and the configure script run it.
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5) Configure and build
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./configure && make -s && make check
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6) Add/update tests
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The tests directory contains regression tests of the dissection of captured
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packets. Those captured packets were saved running tcpdump with option "-w
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sample.pcap". Additional options, such as "-n", are used to create relevant
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and reproducible output; "-#" is used to indicate which particular packets
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have output that differs. The tests are run with the TZ environment
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variable set to GMT0, so that UTC, rather than the local time where the
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tests are being run, is used when "local time" values are printed. The
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actual test compares the current text output with the expected result
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(sample.out) saved from a previous version.
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Any new/updated fields in a dissector must be present in a sample.pcap file
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and the corresponding output file.
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Configuration is set in tests/TESTLIST.
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Each line in this file has the following format:
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test-name sample.pcap sample.out tcpdump-options
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The sample.out file can be produced as follows:
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(cd tests && TZ=GMT0 ../tcpdump -# -n -r sample.pcap tcpdump-options > sample.out)
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Or, for convenience, use "./update-test.sh test-name"
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It is often useful to have test outputs with different verbosity levels
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(none, -v, -vv, -vvv, etc.) depending on the code.
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7) Test with 'make check'
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Don't send a pull request if 'make check' gives failed tests.
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8) Try to rebase your commits to keep the history simple.
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git rebase upstream/master
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(If the rebase fails and you cannot resolve, issue "git rebase --abort"
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and ask for help in the pull request comment.)
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9) Once 100% happy, put your work into your forked repository.
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git push
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10) Initiate and send a pull request
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(See https://help.github.com/articles/using-pull-requests/)
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This will trigger the upstream repository CI tests.
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Code style and generic remarks
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------------------------------
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a) A thorough reading of some other printers code is useful.
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b) Put the normative reference if any as comments (RFC, etc.).
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c) Put the format of packets/headers/options as comments if there is no
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published normative reference.
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d) The printer may receive incomplete packet in the buffer, truncated at any
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random position, for example by capturing with '-s size' option.
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If your code reads and decodes every byte of the protocol packet, then to
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ensure proper and complete bounds checks it would be sufficient to read all
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packet data using the GET_*() macros, typically:
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GET_U_1(p)
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GET_S_1(p)
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GET_BE_U_n(p), n in { 2, 3, 4, 5, 6, 7, 8 }
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GET_BE_S_n(p), n in { 2, 3, 4, 5, 6, 7, 8 }
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If your code uses the macros above only on some packet data, then the gaps
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would have to be bounds-checked using the ND_TCHECK_*() macros:
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ND_TCHECK_n(p), n in { 1, 2, 3, 4, 5, 6, 7, 8, 16 }
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ND_TCHECK_SIZE(p)
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ND_TCHECK_LEN(p, l)
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For the ND_TCHECK_* macros (if not already done):
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Assign: ndo->ndo_protocol = "protocol";
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Define: ND_LONGJMP_FROM_TCHECK before including netdissect.h
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Make sure that the intersection of GET_*() and ND_TCHECK_*() is minimal,
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but at the same time their union covers all packet data in all cases.
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You can test the code via:
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sudo ./tcpdump -s snaplen [-v][v][...] -i lo # in a terminal
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sudo tcpreplay -i lo sample.pcap # in another terminal
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You should try several values for snaplen to do various truncation.
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e) Do invalid packet checks in code: Think that your code can receive in input
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not only a valid packet but any arbitrary random sequence of octets (packet
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- built malformed originally by the sender or by a fuzz tester,
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- became corrupted in transit or for some other reason).
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Print with: nd_print_invalid(ndo); /* to print " (invalid)" */
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f) Use 'struct tok' for indexed strings and print them with
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tok2str() or bittok2str() (for flags).
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g) Avoid empty lines in output of printers.
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h) A commit message must have:
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First line: Capitalized short summary in the imperative (70 chars or less)
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Body: Detailed explanatory text, if necessary. Fold it to approximately
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72 characters. There must be an empty line separating the summary from
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the body.
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i) Avoid non-ASCII characters in code and commit messages.
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j) Use the style of the modified sources.
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k) Don't mix declarations and code
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l) Don't use // for comments
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Not all C compilers accept C++/C99 comments by default.
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m) Avoid trailing tabs/spaces
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