linux-kernel - Re: [syzbot] KASAN: use-after-free Read in jbd2_journal_wait

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Date:   Tue, 8 Feb 2022 17:14:29 +0100
From:   Jan Kara <jack@...e.cz>
To:     syzbot <syzbot+afa2ca5171d93e44b348@...kaller.appspotmail.com>
Cc:     jack@...e.com, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        tytso@....edu, Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: Re: [syzbot] KASAN: use-after-free Read in jbd2_journal_wait_updates

On Tue 08-02-22 04:49:19, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    555f3d7be91a Merge tag '5.17-rc3-ksmbd-server-fixes' of gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17e55852700000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=88e0a6a3dbf057cf
> dashboard link: https://syzkaller.appspot.com/bug?extid=afa2ca5171d93e44b348
> compiler:       Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13b03872700000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+afa2ca5171d93e44b348@...kaller.appspotmail.com

So the syzbot reproducer looks bogus to me but the bug is real.
jbd2_journal_wait_updates() looks at commit_transaction after dropping
j_state_lock and sleeping which is certainly prone to use-after-free
issues.

Funnily, Ritesh's removal of t_handle_lock should "fix" the problem by
removing this dereference. So Ritesh, please just add some reference to
syzbot report and maybe a backport to stable would be warranted.

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR