Re: [syzbot] KASAN: use-after-free Read in jbd2_journal_wait_updates

[Jan Kara]

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@xxxxxxxxxxxxxxxxxxxxxxxxx

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@xxxxxxxx>
SUSE Labs, CR