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syzkaller/docs/syzbot.md
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syzbot

syzbot system continuously fuzzes main Linux kernel branches and automatically reports all found bugs. Direct all questions to syzkaller@googlegroups.com. All syzbot-reported bugs are collected here.

Bug status tracking

syzbot needs to know when a bug is fixed in order to (1) verify that it is in fact fixed and (2) be able to report other similarly-looking crashes (while a bug is considered open all similarly-looking crashes are merged into the existing bug). To understand when a bug is fixed syzbot needs to know what commit fixes the bug; once syzbot knows the commit it will track when the commit reaches all kernel builds on all tracked branches. Only when the commit reaches all builds, the bug is considered closed (new similarly-looking crashes create a new bug).

Communication with syzbot

If you fix a bug reported by syzbot, please add the provided Reported-by tag to the commit. You can also communicate with syzbot by replying to its emails. The commands are:

  • to attach a fixing commit to the bug (if you forgot to add Reported-by tag):
#syz fix: exact-commit-title

It's enough that the commit is merged into any tree, in particular, you don't need to wait for the commit to be merged into upstream tree. syzbot only needs to know the title by which it will appear in tested trees. In case of an error or a title change, you can override the commit simply by sending another #syz fix command.

  • to test a patch for a bug with reproducer:
#syz test: git://repo/address.git branch

and provide the patch inline or as a text attachment. Attachments are more reliable because of email clients splitting lines and messing with whitespaces. syzbot will test the patch on HEAD of the specified git repo/branch. Note: this can be used both for testing fix patches and just for debugging (i.e. adding additional checks to code and testing with them). Note: you may send the request only to syzbot email address, as patches sent to some mailing lists (e.g. netdev, netfilter-devel) will trigger patchwork. After sending an email you should get a reply email with results within an hour.

  • to mark the bug as a duplicate of another syzbot bug:
#syz dup: exact-subject-of-another-report
  • to mark the bug as a one-off invalid report (e.g. induced by a previous memory corruption):
#syz invalid

Note: if the crash happens again, it will cause creation of a new bug report.

Note: all commands must start from beginning of the line.

Note: please keep syzkaller-bugs@googlegroups.com mailing list in CC. It serves as a history of what happened with each bug report.

syzkaller reproducers

syzbot aims at providing stand-alone C reproducers for all reported bugs. However, sometimes it can't extract a reproducer at all, or can only extract a syzkaller reproducer. syzkaller reproducers are programs in a special syzkaller notation and they can be executed on the target system with a little bit more effort. See this for instructions.

A syskaller program can also give you an idea as to what syscalls with what arguments were executed (note that some calls can actually be executed in parallel).

A syzkaller program can be converted to an almost equivalent C source using syz-prog2c utility. syz-prog2c has lots of flags in common with syz-execprog, e.g. -threaded/-collide which control if the syscalls are executed sequentially or in parallel. An example invocation:

syz-prog2c -prog repro.syz.txt -threaded -collide -repeat -procs=8 -sandbox=namespace -tun -tmpdir -waitrepeat

However, note that if syzbot did not provide a C reproducer, it wasn't able to trigger the bug using the C program (though, it can be just because the bug is triggered by a subtle race condition).

Crash does not reproduce?

If the provided reproducer does not work for you, most likely it is related to the fact that you have slightly different setup than syzbot. syzbot has obtained the provided crash report on the provided reproducer on a freshly-booted machine, so the reproducer worked for it somehow.

syzbot uses GCE VMs for testing, but usually it is not important.

If the reproducer exits quickly, try to run it several times, or in a loop. There can be some races involved.

Exact compiler used by syzbot can be found here (245MB).

A qemu-suitable Debian/wheezy image can be found here (1GB, compression somehow breaks it), root ssh key for it is here.

No reproducer at all?

Reproducers are best-effort. syzbot always tries to create reproducers, and once it has one it adds it to the bug. If there is no reproducer referenced in a bug, a reproducer does not exist. There are multiple reasons why syzbot can fail to create a reproducer: some crashes are caused by subtle races and are very hard to reproduce in general; some crashes are caused by global accumulated state in kernel (e.g. lockdep reports); some crashes are caused by non-reproducible coincidences (e.g. an integer 0x12345 happened to reference an existing IPC object) and there is long tail of other reasons.

Is syzbot code available?

Yes, it is here.