192 lines
7.4 KiB
Markdown
192 lines
7.4 KiB
Markdown
|
# Some Information for Contributors
|
||
|
Thank you for considering to make a contribution to tcpdump! Please use the
|
||
|
guidelines below to achieve the best results and experience for everyone.
|
||
|
|
||
|
## How to report bugs and other problems
|
||
|
**To report a security issue (segfault, buffer overflow, infinite loop, arbitrary
|
||
|
code execution etc) please send an e-mail to security@tcpdump.org, do not use
|
||
|
the bug tracker!**
|
||
|
|
||
|
To report a non-security problem (failure to compile, incorrect output in the
|
||
|
protocol printout, missing support for a particular protocol etc) please check
|
||
|
first that it reproduces with the latest stable release of tcpdump and the latest
|
||
|
stable release of libpcap. If it does, please check that the problem reproduces
|
||
|
with the current git master branch of tcpdump and the current git master branch of
|
||
|
libpcap. If it does (and it is not a security-related problem, otherwise see
|
||
|
above), please navigate to the
|
||
|
[bug tracker](https://github.com/the-tcpdump-group/tcpdump/issues)
|
||
|
and check if the problem has already been reported. If it has not, please open
|
||
|
a new issue and provide the following details:
|
||
|
|
||
|
* tcpdump and libpcap version (`tcpdump --version`)
|
||
|
* operating system name and version and any other details that may be relevant
|
||
|
(`uname -a`, compiler name and version, CPU type etc.)
|
||
|
* custom `configure`/`cmake` flags, if any
|
||
|
* statement of the problem
|
||
|
* steps to reproduce
|
||
|
|
||
|
Please note that if you know exactly how to solve the problem and the solution
|
||
|
would not be too intrusive, it would be best to contribute some development time
|
||
|
and to open a pull request instead as discussed below.
|
||
|
|
||
|
Still not sure how to do? Feel free to
|
||
|
[subscribe to the mailing list](https://www.tcpdump.org/#mailing-lists)
|
||
|
and ask!
|
||
|
|
||
|
|
||
|
## How to add new code and to update existing code
|
||
|
|
||
|
0) Check that there isn't a pull request already opened for the changes you
|
||
|
intend to make.
|
||
|
|
||
|
1) [Fork](https://help.github.com/articles/fork-a-repo/) the Tcpdump
|
||
|
[repository](https://github.com/the-tcpdump-group/tcpdump).
|
||
|
|
||
|
2) The easiest way to test your changes on multiple operating systems and
|
||
|
architectures is to let the upstream CI test your pull request (more on
|
||
|
this below).
|
||
|
|
||
|
3) Setup your git working copy
|
||
|
```
|
||
|
git clone https://github.com/<username>/tcpdump.git
|
||
|
cd tcpdump
|
||
|
git remote add upstream https://github.com/the-tcpdump-group/tcpdump
|
||
|
git fetch upstream
|
||
|
```
|
||
|
|
||
|
4) Do a `touch .devel` in your working directory.
|
||
|
Currently, the effect is
|
||
|
* add (via `configure`, in `Makefile`) some warnings options (`-Wall`,
|
||
|
`-Wmissing-prototypes`, `-Wstrict-prototypes`, ...) to the compiler if it
|
||
|
supports these options,
|
||
|
* have the `Makefile` support `make depend` and the `configure` script run it.
|
||
|
|
||
|
5) Configure and build
|
||
|
```
|
||
|
./configure && make -s && make check
|
||
|
```
|
||
|
|
||
|
6) Add/update tests
|
||
|
The `tests` directory contains regression tests of the dissection of captured
|
||
|
packets. Those captured packets were saved running tcpdump with option
|
||
|
`-w sample.pcap`. Additional options, such as `-n`, are used to create relevant
|
||
|
and reproducible output; `-#` is used to indicate which particular packets
|
||
|
have output that differs. The tests are run with the `TZ` environment
|
||
|
variable set to `GMT0`, so that UTC, rather than the local time where the
|
||
|
tests are being run, is used when "local time" values are printed. The
|
||
|
actual test compares the current text output with the expected result
|
||
|
(`sample.out`) saved from a previous version.
|
||
|
|
||
|
Any new/updated fields in a dissector must be present in a `sample.pcap` file
|
||
|
and the corresponding output file.
|
||
|
|
||
|
Configuration is set in `tests/TESTLIST`.
|
||
|
Each line in this file has the following format:
|
||
|
```
|
||
|
test-name sample.pcap sample.out tcpdump-options
|
||
|
```
|
||
|
|
||
|
The `sample.out` file can be produced as follows:
|
||
|
```
|
||
|
(cd tests && TZ=GMT0 ../tcpdump -# -n -r sample.pcap tcpdump-options > sample.out)
|
||
|
```
|
||
|
|
||
|
Or, for convenience, use `./update-test.sh test-name`
|
||
|
|
||
|
It is often useful to have test outputs with different verbosity levels
|
||
|
(none, `-v`, `-vv`, `-vvv`, etc.) depending on the code.
|
||
|
|
||
|
7) Test using `make check` (current build options) and `./build_matrix.sh`
|
||
|
(a multitude of build options, build systems and compilers). If you can,
|
||
|
test on more than one operating system. Don't send a pull request until
|
||
|
all tests pass.
|
||
|
|
||
|
8) Try to rebase your commits to keep the history simple.
|
||
|
```
|
||
|
git fetch upstream
|
||
|
git rebase upstream/master
|
||
|
```
|
||
|
(If the rebase fails and you cannot resolve, issue `git rebase --abort`
|
||
|
and ask for help in the pull request comment.)
|
||
|
|
||
|
9) Once 100% happy, put your work into your forked repository using `git push`.
|
||
|
|
||
|
10) [Initiate and send](https://help.github.com/articles/using-pull-requests/)
|
||
|
a pull request.
|
||
|
This will trigger the upstream repository CI tests.
|
||
|
|
||
|
|
||
|
## Code style and generic remarks
|
||
|
* A thorough reading of some other printers code is useful.
|
||
|
|
||
|
* Put the normative reference if any as comments (RFC, etc.).
|
||
|
|
||
|
* Put the format of packets/headers/options as comments if there is no
|
||
|
published normative reference.
|
||
|
|
||
|
* The printer may receive incomplete packet in the buffer, truncated at any
|
||
|
random position, for example by capturing with `-s size` option.
|
||
|
If your code reads and decodes every byte of the protocol packet, then to
|
||
|
ensure proper and complete bounds checks it would be sufficient to read all
|
||
|
packet data using the `GET_*()` macros, typically:
|
||
|
```
|
||
|
GET_U_1(p)
|
||
|
GET_S_1(p)
|
||
|
GET_BE_U_n(p), n in { 2, 3, 4, 5, 6, 7, 8 }
|
||
|
GET_BE_S_n(p), n in { 2, 3, 4, 5, 6, 7, 8 }
|
||
|
```
|
||
|
If your code uses the macros above only on some packet data, then the gaps
|
||
|
would have to be bounds-checked using the `ND_TCHECK_*()` macros:
|
||
|
```
|
||
|
ND_TCHECK_n(p), n in { 1, 2, 3, 4, 5, 6, 7, 8, 16 }
|
||
|
ND_TCHECK_SIZE(p)
|
||
|
ND_TCHECK_LEN(p, l)
|
||
|
```
|
||
|
For the `ND_TCHECK_*` macros (if not already done):
|
||
|
* Assign: `ndo->ndo_protocol = "protocol";`
|
||
|
* Define: `ND_LONGJMP_FROM_TCHECK` before including `netdissect.h`
|
||
|
* Make sure that the intersection of `GET_*()` and `ND_TCHECK_*()` is minimal,
|
||
|
but at the same time their union covers all packet data in all cases.
|
||
|
|
||
|
You can test the code via:
|
||
|
```
|
||
|
sudo ./tcpdump -s snaplen [-v][v][...] -i lo # in a terminal
|
||
|
sudo tcpreplay -i lo sample.pcap # in another terminal
|
||
|
```
|
||
|
You should try several values for snaplen to do various truncation.
|
||
|
|
||
|
* Do invalid packet checks in code: Think that your code can receive in input
|
||
|
not only a valid packet but any arbitrary random sequence of octets (packet
|
||
|
* built malformed originally by the sender or by a fuzz tester,
|
||
|
* became corrupted in transit or for some other reason).
|
||
|
|
||
|
Print with: `nd_print_invalid(ndo); /* to print " (invalid)" */`
|
||
|
|
||
|
* Use `struct tok` for indexed strings and print them with
|
||
|
`tok2str()` or `bittok2str()` (for flags).
|
||
|
|
||
|
* Avoid empty lines in output of printers.
|
||
|
|
||
|
* A commit message must have:
|
||
|
```
|
||
|
First line: Capitalized short summary in the imperative (50 chars or less)
|
||
|
|
||
|
If the commit concerns a protocol, the summary line must start with
|
||
|
"protocol: ".
|
||
|
|
||
|
Body: Detailed explanatory text, if necessary. Fold it to approximately
|
||
|
72 characters. There must be an empty line separating the summary from
|
||
|
the body.
|
||
|
```
|
||
|
|
||
|
* Avoid non-ASCII characters in code and commit messages.
|
||
|
|
||
|
* Use the style of the modified sources.
|
||
|
|
||
|
* Don't mix declarations and code.
|
||
|
|
||
|
* Don't use `//` for comments.
|
||
|
Not all C compilers accept C++/C99 comments by default.
|
||
|
|
||
|
* Avoid trailing tabs/spaces
|