From a61d90d75d0f9e86432c45b496b4b0fbf0fd03dc Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Tue, 9 Jun 2009 16:26:26 -0700 Subject: [PATCH] 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 Cc: Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/jbd/commit.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c index 06560c520f49..618e21c0b7a3 100644 --- a/fs/jbd/commit.c +++ b/fs/jbd/commit.c @@ -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);