linux-kernel - Re: [syzbot] KASAN: use-after-free Read in xfs_qm_dqfree

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Message-ID: <20221206033450.GS3600936@dread.disaster.area>
Date:   Tue, 6 Dec 2022 14:34:50 +1100
From:   Dave Chinner <david@...morbit.com>
To:     syzbot <syzbot+912776840162c13db1a3@...kaller.appspotmail.com>
Cc:     djwong@...nel.org, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Read in xfs_qm_dqfree_one

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....

-Dave.

-- 
Dave Chinner
david@...morbit.com