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

------------------

From: Dan Carpenter <redacted>

commit bb3d132a24cd8bf5e7773b2d9f9baa58b07a7dae upstream.

The ext4_get_group_desc() function returns NULL on error, and
ext4_free_inodes_count() function dereferences it without checking.
There is a check on the next line, but it's too late.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Carpenter <redacted>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/ext4/ialloc.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c

@@ -488,10 +488,12 @@ fallback_retry:
 	for (i = 0; i < ngroups; i++) {
 		grp = (parent_group + i) % ngroups;
 		desc = ext4_get_group_desc(sb, grp, NULL);
-		grp_free = ext4_free_inodes_count(sb, desc);
-		if (desc && grp_free && grp_free >= avefreei) {
-			*group = grp;
-			return 0;
+		if (desc) {
+			grp_free = ext4_free_inodes_count(sb, desc);
+			if (grp_free && grp_free >= avefreei) {
+				*group = grp;
+				return 0;
+			}
 		}
 	}