[PATCH 0/22] fsnotify: Avoid SRCU stalls with fanotify permission events

[Paul Moore]

On Thu, Dec 22, 2016 at 4:15 AM, Jan Kara <jack at suse.cz> wrote:
> Hello,
>
> currently, fanotify waits for response to a permission even from userspace
> process while holding fsnotify_mark_srcu lock. That has a consequence that
> when userspace process takes long to respond or does not respond at all,
> fsnotify_mark_srcu period cannot ever complete blocking reclaim of any
> notification marks and also blocking any process that did synchronize_srcu()
> on fsnotify_mark_srcu. Effectively, this eventually blocks anybody interacting
> with the notification subsystem. Miklos has some real world reports of this
> happening. Although this in principle a problem of broken userspace
> application (which futhermore has to have CAP_SYS_ADMIN in init_user_ns, so
> it is not a security problem), it is still nasty that a simple error can
> block the kernel like this.
>
> This patch set solves this problem ...
>
> Patches have survived testing with inotify/fanotify tests in LTP. I didn't test
> audit - Paul can you give these patches some testing?  Since some of the
> changes are really non-trivial, I'd welcome if someone reviewed the patch set.

I'm going to take a look at the audit related patches right now,
expect some feedback shortly.

In the meantime, if you wanted to play a bit with some simple audit
regression tests, check out the testsuite below:

* https://github.com/linux-audit/audit-testsuite

... it is still rather simplistic, but the tests in tests/file_* and
tests/exec_name should do some basic exercises of the audit code that
leverages fsnotify.  If nothing else, it should give you some ideas
about how you might stress this a bit more with audit.

-- 
paul moore
www.paul-moore.com