[patch 38/60] ext4: fix header check in ext4_ext_search_right() for deep extent trees.

[Greg KH]

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

------------------
From: Eric Sandeen <sandeen@xxxxxxxxxx>

(cherry picked from commit 395a87bfefbc400011417e9eaae33169f9f036c0)

The ext4_ext_search_right() function is confusing; it uses a
"depth" variable which is 0 at the root and maximum at the leaves,
but the on-disk metadata uses a "depth" (actually eh_depth) which
is opposite: maximum at the root, and 0 at the leaves.

The ext4_ext_check_header() function is given a depth and checks
the header agaisnt that depth; it expects the on-disk semantics,
but we are giving it the opposite in the while loop in this
function.  We should be giving it the on-disk notion of "depth"
which we can get from (p_depth - depth) - and if you look, the last
(more commonly hit) call to ext4_ext_check_header() does just this.

Sending in the wrong depth results in (incorrect) messages
about corruption:

EXT4-fs error (device sdb1): ext4_ext_search_right: bad header
in inode #2621457: unexpected eh_depth - magic f30a, entries 340,
max 340(0), depth 1(2)

http://bugzilla.kernel.org/show_bug.cgi?id=12821

Reported-by: David Dindorp <ddi@xxxxxxxx>
Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
 fs/ext4/extents.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1118,7 +1118,8 @@ ext4_ext_search_right(struct inode *inod
 	struct ext4_extent_idx *ix;
 	struct ext4_extent *ex;
 	ext4_fsblk_t block;
-	int depth, ee_len;
+	int depth;	/* Note, NOT eh_depth; depth from top of tree */
+	int ee_len;
 
 	BUG_ON(path == NULL);
 	depth = path->p_depth;
@@ -1177,7 +1178,8 @@ ext4_ext_search_right(struct inode *inod
 		if (bh == NULL)
 			return -EIO;
 		eh = ext_block_hdr(bh);
-		if (ext4_ext_check_header(inode, eh, depth)) {
+		/* subtract from p_depth to get proper eh_depth */
+		if (ext4_ext_check_header(inode, eh, path->p_depth - depth)) {
 			put_bh(bh);
 			return -EIO;
 		}


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