On Tue 26-04-22 11:31:24, Samuel Mendoza-Jonas wrote:
> On Thu, Feb 10, 2022 at 09:07:11PM +0530, Ritesh Harjani wrote:
> > jbd2_journal_wait_updates() is called with j_state_lock held. But if
> > there is a commit in progress, then this transaction might get committed
> > and freed via jbd2_journal_commit_transaction() ->
> > jbd2_journal_free_transaction(), when we release j_state_lock.
> > So check for journal->j_running_transaction everytime we release and
> > acquire j_state_lock to avoid use-after-free issue.
> >
> > Fixes: 4f98186848707f53 ("jbd2: refactor wait logic for transaction updates into a common function")
> > Reported-and-tested-by: syzbot+afa2ca5171d93e44b348@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
>
> Hi Ritesh,
>
> Looking at the refactor in the commit this fixes, I believe the same
> issue is present prior to the refactor, so this would apply before 5.17
> as well.
> I've posted a backport for 4.9-4.19 and 5.4-5.16 to stable here:
> https://lore.kernel.org/stable/20220426182702.716304-1-samjonas@xxxxxxxxxx/T/#t
>
> Please have a look and let me know if you agree.
Actually the refactor was indeed the cause for use-after-free. The original
code in jbd2_journal_lock_updates() was like:
/* Wait until there are no running updates */
while (1) {
transaction_t *transaction = journal->j_running_transaction;
if (!transaction)
break;
spin_lock(&transaction->t_handle_lock);
prepare_to_wait(&journal->j_wait_updates, &wait,
TASK_UNINTERRUPTIBLE);
if (!atomic_read(&transaction->t_updates)) {
spin_unlock(&transaction->t_handle_lock);
finish_wait(&journal->j_wait_updates, &wait);
break;
}
spin_unlock(&transaction->t_handle_lock);
write_unlock(&journal->j_state_lock);
schedule();
finish_wait(&journal->j_wait_updates, &wait);
write_lock(&journal->j_state_lock);
}
So you can see the code was indeed careful enough to not touch
t_handle_lock after sleeping. The code in jbd2_journal_commit_transaction()
did touch t_handle_lock but there it didn't matter because nobody else
besides the task running jbd2_journal_commit_transaction() can free the
transaction...
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
