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ext4: Fix buffer double free in ext4_alloc_branch() 

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>
Cc: stable@vger.kernel.org
This commit is contained in:
Jan Kara 2014-06-15 23:46:28 -04:00 committed by Theodore Ts'o
parent 7171511eae
commit c5c7b8ddfb
1 changed files with 7 additions and 1 deletions
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8
fs/ext4/indirect.c
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@ -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],