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

[Amir Goldstein]

On Thu, Dec 22, 2016 at 10:58 PM, Paul Moore <paul at paul-moore.com> wrote:
> 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.
>


Mmm that's interesting. I was looking for a good place to start with a proper
testsuite for fsnotify.
It seems like the 2 subsystems could use the same testsuite.

I will look into it.

Thanks!