[PATCH 3.12 109/170] ext4: Fix buffer double free in ext4_alloc_branch()

Jiri Slaby
2014-07-18T13:57:27Z

From: Jan Kara <jack@suse.cz>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

commit c5c7b8ddfbf8cb3b2291e515a34ab1b8982f5a2d upstream.

Error recovery in ext4_alloc_branch() calls ext4_forget() even for
buffer corresponding to indirect block it did not allocate. This leads
to brelse() being called twice for that buffer (once from ext4_forget()
and once from cleanup in ext4_ind_map_blocks()) leading to buffer use
count misaccounting. Eventually (but often much later because there
are other users of the buffer) we will see messages like:
VFS: brelse: Trying to free free buffer

Another manifestation of this problem is an error:
JBD2 unexpected failure: jbd2_journal_revoke: !buffer_revoked(bh);
inconsistent data on disk

The fix is easy - don't forget buffer we did not allocate. Also add an
explanatory comment because the indexing at ext4_alloc_branch() is
somewhat subtle.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
fs/ext4/indirect.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 594009f5f523..3b91d240da4d 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -389,7 +389,13 @@ static int ext4_alloc_branch(handle_t *handle, struct inode *inode,
return 0;
failed:
for (; i >= 0; i--) {
- if (i != indirect_blks && branch[i].bh)
+ /*
+ * We want to ext4_forget() only freshly allocated indirect
+ * blocks. Buffer for new_blocks[i-1] is at branch[i].bh and
+ * buffer at branch[0].bh is indirect block / inode already
+ * existing before ext4_alloc_branch() was called.
+ */
+ if (i > 0 && i != indirect_blks && branch[i].bh)
ext4_forget(handle, 1, inode, branch[i].bh,
branch[i].bh->b_blocknr);
ext4_free_blocks(handle, inode, NULL, new_blocks[i],
--
2.0.0