deadlock bug related to bpf,audit subsystems

[Paul Moore]

On Thu, Mar 18, 2021 at 1:44 PM Paul Moore <paul at paul-moore.com> wrote:
> On Thu, Mar 18, 2021 at 12:57 PM Serhei Makarov <smakarov at redhat.com> wrote:
> > On Thu, Mar 18, 2021 at 10:43 AM Serhei Makarov <smakarov at redhat.com> wrote:
> > > Jiri Olsa also reports seeing a similar deadlock at v5.10. I'm in the
> > > middle of double-checking my bisection which ended up at a
> > > seemingly-unrelated commit [2]
> > >
> > > [1] https://bugzilla.redhat.com/show_bug.cgi?id=1938312
> > > [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.11-rc7&id=2dcb3964544177c51853a210b6ad400de78ef17d
> >
> > I've confirmed that my first bisection was incorrect by testing
> > @1c2f67308af4 mm: thp: fix MADV_REMOVE deadlock on shmem THP
> > and reproducing the deadlock. Previously this commit was marked as
> > good, so it seems a kernel with the bug can sometimes pass the test.
> >
> > I'll double check rc6 next since I have the kernel handy. If
> > 5.11.0-rc6 can also be made to fail, with Jiri Olsa's report it'd be
> > necessary to do a wider search.
> > There may be commits with intent similar to
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8d92db5c04d103
> > which tightened some of the behaviour of kernel reads, but affecting
> > the audit subsystem?
> > The actual stack trace that leads to deadlock goes through
> > security_locked_down() which was present since the original patch
> > reworking probe_read into separate probe_read_{user,kernel} helpers
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.11-rc7&id=6ae08ae3dea2
>
> Added thee SELinux list to the To/CC line; they should really be
> involved.  I'm also CC'ing the LSM list for good measure as there may
> be other people that care about this.

Argh, hit send a bit too quickly :/

> FYI, the first instance of this thread that I saw can be found here
> via the linux-audit list:
>
> https://lore.kernel.org/linux-audit/CANYvDQN7H5tVp47fbYcRasv4XF07eUbsDwT_eDCHXJUj43J7jQ@mail.gmail.com/

-- 
paul moore
www.paul-moore.com