Commit a61d90d7 authored Jun 09, 2009 by Jan Kara Committed by Linus Torvalds Jun 09, 2009

jbd: fix race in buffer processing in commit code



In commit code, we scan buffers attached to a transaction.  During this
scan, we sometimes have to drop j_list_lock and then we recheck whether
the journal buffer head didn't get freed by journal_try_to_free_buffers().
 But checking for buffer_jbd(bh) isn't enough because a new journal head
could get attached to our buffer head.  So add a check whether the journal
head remained the same and whether it's still at the same transaction and
list.

This is a nasty bug and can cause problems like memory corruption (use after
free) or trigger various assertions in JBD code (observed).

Signed-off-by: Jan Kara <jack@suse.cz>
Cc: <stable@kernel.org>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 463aea1a

fs/jbd/commit.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -241,7 +241,7 @@ write_out_data:
		spin_lock(&journal->j_list_lock);
		}
		/* Someone already cleaned up the buffer? */
		if (!buffer_jbd(bh)
		if (!buffer_jbd(bh) \|\| bh2jh(bh) != jh
		\|\| jh->b_transaction != commit_transaction
		\|\| jh->b_jlist != BJ_SyncData) {
		jbd_unlock_bh_state(bh);
		@@ -478,7 +478,9 @@ void journal_commit_transaction(journal_t *journal)
		spin_lock(&journal->j_list_lock);
		continue;
		}
		if (buffer_jbd(bh) && jh->b_jlist == BJ_Locked) {
		if (buffer_jbd(bh) && bh2jh(bh) == jh &&
		jh->b_transaction == commit_transaction &&
		jh->b_jlist == BJ_Locked) {
		__journal_unfile_buffer(jh);
		jbd_unlock_bh_state(bh);
		journal_remove_journal_head(bh);

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