From dbfcef6b0f4012c57bc0b6e0e660d5ed12a5eaed Mon Sep 17 00:00:00 2001 From: Sahitya Tummala Date: Wed, 1 Feb 2017 20:49:35 -0500 Subject: [PATCH] jbd2: fix use after free in kjournald2() 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 Signed-off-by: Theodore Ts'o --- fs/jbd2/journal.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c index a097048ed1a3..85d1483939b2 100644 --- 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; }