On Wed 09-02-22 15:26:47, Ritesh Harjani wrote: > On 22/02/08 05:14PM, Jan Kara wrote: > > 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. > > Yes, thanks for taking a look at it. > > > > > 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. > > > > This actually looks like a regression because of commit [1]. > So I am thinking of sending a separate patch [2] as a fix for this (after my > testing). Yeah, and my fault for not catching this during review :-|. Anyway the proposed fix looks good. > Not sure why fstests testing didn't pick this up (given it's a common race), > or is it because of my recent removal of CONFIG_KASAN from my testing :( > > I will try a full "auto" test with CONFIG_KASAN enabled and see if we could hit > this in fstests or not. If not then I will work towards adding a targetted test > to capture such race. Yeah, without KASAN this could lead to memory corruption by the spin_lock() but in most cases it will just pass by unnoticed because the memory does not get reused so quickly. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
