4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Sahitya Tummala <stummala@xxxxxxxxxxxxxx>
commit dbfcef6b0f4012c57bc0b6e0e660d5ed12a5eaed upstream.
Below is the synchronization issue between unmount and kjournald2
contexts, which results into use after free issue in kjournald2().
Fix this issue by using journal->j_state_lock to synchronize the
wait_event() done in journal_kill_thread() and the wake_up() done
in kjournald2().
TASK 1:
umount cmd:
|--jbd2_journal_destroy() {
|--journal_kill_thread() {
write_lock(&journal->j_state_lock);
journal->j_flags |= JBD2_UNMOUNT;
...
write_unlock(&journal->j_state_lock);
wake_up(&journal->j_wait_commit); TASK 2 wakes up here:
kjournald2() {
...
checks JBD2_UNMOUNT flag and calls goto end-loop;
...
end_loop:
write_unlock(&journal->j_state_lock);
journal->j_task = NULL; --> If this thread gets
pre-empted here, then TASK 1 wait_event will
exit even before this thread is completely
done.
wait_event(journal->j_wait_done_commit, journal->j_task == NULL);
...
write_lock(&journal->j_state_lock);
write_unlock(&journal->j_state_lock);
}
|--kfree(journal);
}
}
wake_up(&journal->j_wait_done_commit); --> this step
now results into use after free issue.
}
Signed-off-by: Sahitya Tummala <stummala@xxxxxxxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Cc: Amit Pundir <amit.pundir@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/jbd2/journal.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -276,11 +276,11 @@ loop:
goto loop;
end_loop:
- write_unlock(&journal->j_state_lock);
del_timer_sync(&journal->j_commit_timer);
journal->j_task = NULL;
wake_up(&journal->j_wait_done_commit);
jbd_debug(1, "Journal thread exiting.\n");
+ write_unlock(&journal->j_state_lock);
return 0;
}