Re: [syzbot] WARNING in mntput_no_expire (2)

Jens Axboe
2021-04-06T15:37:24Z

On 4/6/21 8:23 AM, Al Viro wrote:
> On Tue, Apr 06, 2021 at 02:15:01PM +0000, Al Viro wrote:
>
>> I'm referring to the fact that your diff is with an already modified path_lookupat()
>> _and_ those modifications have managed to introduce a bug your patch reverts.
>> No terminate_walk() paired with that path_init() failure, i.e. path_init() is
>> responsible for cleanups on its (many) failure exits...
>
> I can't tell without seeing the variant your diff is against, but at a guess
> it had a non-trivial amount of trouble with missed rcu_read_unlock() in
> cases when path_init() fails after having done rcu_read_lock(). For trivial
> testcase, consider passing -1 for dfd, so that it would fail with -EBADF.
> Or passing 0 for dfd and "blah" for name (assuming your stdin is not a directory).
> Sure, you could handle those in path_init() (or delay grabbing rcu_read_lock()
> in there, spreading it in a bunch of branches), but duplicated cleanup logics
> for a bunch of failure exits is asking for trouble.

Thanks for taking care of this Al, fwiw I'm (mostly) out on vacation.

--
Jens Axboe