Re: CVE-2020-29373 reproducer fails on v5.11

[Petr Vorel <pvorel@suse.cz>]

Hi Pavel,

> On 12/02/2021 12:49, Petr Vorel wrote:
> > Hi all,

> >> On 2/10/21 12:32 PM, Pavel Begunkov wrote:
> >>> On 10/02/2021 19:08, Petr Vorel wrote:
> >>>> Hi all,

> >>>> I found that the reproducer for CVE-2020-29373 from Nicolai Stange (source attached),
> >>>> which was backported to LTP as io_uring02 by Martin Doucha [1] is failing since
> >>>> 10cad2c40dcb ("io_uring: don't take fs for recvmsg/sendmsg") from v5.11-rc1.

> >>> Thanks for letting us know, we need to revert it

> >> I'll queue up a revert. Would also be nice to turn that into
> >> a liburing regression test.

> > Jens (or others), could you please have look that the other commit 907d1df30a51
> > ("io_uring: fix wqe->lock/completion_lock deadlock") from v5.11-rc6 didn't cause
> > any regression? Changed behavior causing io_uring02 test [1] and the original
> > reproducer [2] to fail is probably a test bug, but better double check that.

> Thanks for keeping an eye on it. That's on the test because DRAIN doesn't
> punt to worker threads anymore, and DRAIN is used for those prepended
> requests.

> Can we just use IOSQE_ASYNC instead and fallback to DRAIN for older kernels
> as you mentioned? It would be much more reliable. Or replace IOSQE_IO_DRAIN
> with IOSQE_IO_LINK, but there are nuances to that... 

Thanks for your tips!

Kind regards,
Petr

> > Kind regards,
> > Petr

> > [1] https://github.com/linux-test-project/ltp/tree/master/testcases/kernel/syscalls/io_uring/io_uring02.c
> > [2] https://lore.kernel.org/io-uring/YCQvL8%2FDMNVLLuuf@pevik/