reiserfs: Fix use after free in journal teardown

If do_journal_release() races with do_journal_end() which requeues
delayed works for transaction flushing, we can leave work items for
flushing outstanding transactions queued while freeing them. That
results in use after free and possible crash in run_timers_softirq().

Fix the problem by not requeueing works if superblock is being shut down
(MS_ACTIVE not set) and using cancel_delayed_work_sync() in
do_journal_release().

CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>

fs/reiserfs/journal.c

@@ -1947,8 +1947,6 @@ static int do_journal_release(struct reiserfs_transaction_handle *th,
 		}
 	}
 
-	/* wait for all commits to finish */
-	cancel_delayed_work(&SB_JOURNAL(sb)->j_work);
 
 	/*
 	 * We must release the write lock here because
@@ -1956,8 +1954,14 @@ static int do_journal_release(struct reiserfs_transaction_handle *th,
 	 */
 	reiserfs_write_unlock(sb);
 
+	/*
+	 * Cancel flushing of old commits. Note that neither of these works
+	 * will be requeued because superblock is being shutdown and doesn't
+	 * have MS_ACTIVE set.
+	 */
 	cancel_delayed_work_sync(&REISERFS_SB(sb)->old_work);
-	flush_workqueue(REISERFS_SB(sb)->commit_wq);
+	/* wait for all commits to finish */
+	cancel_delayed_work_sync(&SB_JOURNAL(sb)->j_work);
 
 	free_journal_ram(sb);
 
@@ -4292,9 +4296,15 @@ static int do_journal_end(struct reiserfs_transaction_handle *th, int flags)
 	if (flush) {
 		flush_commit_list(sb, jl, 1);
 		flush_journal_list(sb, jl, 1);
-	} else if (!(jl->j_state & LIST_COMMIT_PENDING))
-		queue_delayed_work(REISERFS_SB(sb)->commit_wq,
-				   &journal->j_work, HZ / 10);
+	} else if (!(jl->j_state & LIST_COMMIT_PENDING)) {
+		/*
+		 * Avoid queueing work when sb is being shut down. Transaction
+		 * will be flushed on journal shutdown.
+		 */
+		if (sb->s_flags & MS_ACTIVE)
+			queue_delayed_work(REISERFS_SB(sb)->commit_wq,
+					   &journal->j_work, HZ / 10);
+	}
 
 	/*
 	 * if the next transaction has any chance of wrapping, flush

fs/reiserfs/super.c

@@ -100,7 +100,11 @@ void reiserfs_schedule_old_flush(struct super_block *s)
 	struct reiserfs_sb_info *sbi = REISERFS_SB(s);
 	unsigned long delay;
 
-	if (s->s_flags & MS_RDONLY)
+	/*
+	 * Avoid scheduling flush when sb is being shut down. It can race
+	 * with journal shutdown and free still queued delayed work.
+	 */
+	if (s->s_flags & MS_RDONLY || !(s->s_flags & MS_ACTIVE))
 		return;
 
 	spin_lock(&sbi->old_work_lock);