Re: [syzbot] KASAN: use-after-free Read in xfs_qm_dqfree_one

Dave Chinner
2022-12-06T20:58:59Z

On Tue, Dec 06, 2022 at 12:06:10PM +0100, Dmitry Vyukov wrote:
> On Tue, 6 Dec 2022 at 04:34, Dave Chinner <david@fromorbit.com> wrote:
> >
> > On Mon, Dec 05, 2022 at 07:12:15PM -0800, syzbot wrote:
> > > Hello,
> > >
> > > syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> > > INFO: rcu detected stall in corrupted
> > >
> > > rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { P4122 } 2641 jiffies s: 2877 root: 0x0/T
> > > rcu: blocking rcu_node structures (internal RCU debug):
> >
> > I'm pretty sure this has nothing to do with the reproducer - the
> > console log here:
> >
> > > Tested on:
> > >
> > > commit: bce93322 proc: proc_skip_spaces() shouldn't think it i..
> > > git tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=1566216b880000
> >
> > indicates that syzbot is screwing around with bluetooth, HCI,
> > netdevsim, bridging, bonding, etc.
> >
> > There's no evidence that it actually ran the reproducer for the bug
> > reported in this thread - there's no record of a single XFS
> > filesystem being mounted in the log....
> >
> > It look slike someone else also tried a private patch to fix this
> > problem (which was obviously broken) and it failed with exactly the
> > same RCU warnings. That was run from the same commit id as the
> > original reproducer, so this looks like either syzbot is broken or
> > there's some other completely unrelated problem that syzbot is
> > tripping over here.
> >
> > Over to the syzbot people to debug the syzbot failure....
>
> Hi Dave,
>
> It's not uncommon for a single program to trigger multiple bugs.
> That's what happens here. The rcu stall issue is reproducible with
> this test program.
> In such cases you can either submit more test requests, or test manually.

So you're telling us syzbot reproducers are unreliable and we are
expected to play whack-a-mole with test resubmission until we get
the result we want?

How do I tell syzbot to resubmit the same patch for testing without
having to send the same patch to syzbot via email again? Can I
retrigger a new test run through the web interface?

-Dave.
--
Dave Chinner
david@fromorbit.com