Trinity

A Linux System call fuzz tester.

What is it?.

The basic idea is fairly simple. As 'fuzz testing' suggests, we call syscalls at random, with random arguments.
Not an original idea, and one that has been done many times before on Linux, and on other operating systems.
Where Trinity differs is that the arguments it passes are not purely random.

We found some bugs in the past by just passing random values, but once the *really* dumb bugs were found, these dumb fuzzers would just run and run. The problem was if a syscall took for example a file descriptor as an argument, one of the first things it would try to do was validate that fd. Being garbage, the kernel would just reject it as -EINVAL of course. So on startup, Trinity creates a list of file descriptors, by opening pipes, scanning sysfs, procfs, /dev, and creates a bunch of sockets using random network protocols. Then when a syscall needs an fd, it gets passed one of these at random.

File descriptors aren't the only thing Trinity knows about. Every syscall has its arguments annotated, and where possible it tries to provide something at least semi-sensible. "Length" arguments for example get passed one of a whole bunch of potentially interesting values. (Powers of 2 +/-1 are a good choice for triggering off-by-one bugs it seems).

Trinity also shares those file descriptors between multiple threads, which causes havoc sometimes.

If a child process successfully creates an mmap, the pointer is stored, and fed to subsequent syscalls, sometimes with hilarious results.

Trinity supports Alpha, Aarch64, ARM, i386, IA-64, MIPS, PowerPC-64, S390, S390x, SPARC-64, x86-64.
Adding support for additional architectures is a small amount of work mostly involving just defining the order of the syscall table.
See Documentation/HACKING for details.

How do I use it?.

If you run Trinity without any arguments as a non-root user, it will scan for fd's as mentioned above, then create a number of child processes (depending on how many processors you have). These child processes are where the 'call the syscall' happens. It's done in child processes so that if a syscall causes a segfault, trinity will respawn a new thread to take its place. Likewise, if a syscall hangs for more than a few seconds, it will get killed.

I recommend not running it on machines containing data you care about. It's entirely plausible that trinity could start calling unlink() on files it randomly finds. You might also want to make sure that there are no nfs or similar filesystems mounted for the same reason.

With that warning out of the way: Trinity has a neat feature called 'victim files'. You can point at a directory with -V and it will use anything it finds in there as potential sources when it needs a file descriptor. If this is somewhere on NFS for example, this will cause a bunch of filesystem related syscalls over NFS to occur, which might shake out NFS related bugs. Get the idea ?

There's a more extensive README in the source distribution which details all the extra parameters. Also recommended reading, are the examples in scripts/ which should give some ideas.

Known problems ?
  • There are almost always new kernel bugs being triggered by trinity. You may want to check the bugs found list before reporting, to see if it's something unique.
  • Sometimes, trinity causes the oom-killer to trigger. As long as the oom-killer picks the right process (ie, one of the trinity children, and not dbus, or NetworkManager etc) then this is working as designed.
  • There's a fair amount of "noise" printk's in the kernel that Trinity triggers. I recommend patching them out as you come across them.
  • If you do find and report a new bug, please Cc me, and mention that you found it with Trinity, so I can add it to the bugs found list.

Downloads:
  • Latest release is v1.3, released on Dec 20th 2013.
  • The git tree for trinity lives at https://github.com/kernelslacker/trinity.git. (Please don't send me github pull requests, send email instead).
  • snapshot tarballs are created every hour.

Contact:
There is a mailing list for trinity hosted at vger.kernel.org.
To subscribe, send a mail with "subscribe trinity" in the body to [email protected]
If you get oopses, send them to [email protected] with the relevant maintainer Cc'd. (I'd appreciate a Cc too <davej atsign redhat.com>, and please mention that you used Trinity to trigger it).

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