[PATCH 4.9 241/329] Btrfs: fix NULL pointer dereference in log_dir_items

[Greg Kroah-Hartman]

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

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

From: Liu Bo <bo.liu@xxxxxxxxxxxxxxxxx>

[ Upstream commit 80c0b4210a963e31529e15bf90519708ec947596 ]

0, 1 and <0 can be returned by btrfs_next_leaf(), and when <0 is
returned, path->nodes[0] could be NULL, log_dir_items lacks such a
check for <0 and we may run into a null pointer dereference panic.

Fixes: e02119d5a7b4 ("Btrfs: Add a write ahead tree log to optimize synchronous operations")
Reviewed-by: Nikolay Borisov <nborisov@xxxxxxxx>
Signed-off-by: Liu Bo <bo.liu@xxxxxxxxxxxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/btrfs/tree-log.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -3399,8 +3399,11 @@ static noinline int log_dir_items(struct
 		 * from this directory and from this transaction
 		 */
 		ret = btrfs_next_leaf(root, path);
-		if (ret == 1) {
-			last_offset = (u64)-1;
+		if (ret) {
+			if (ret == 1)
+				last_offset = (u64)-1;
+			else
+				err = ret;
 			goto done;
 		}
 		btrfs_item_key_to_cpu(path->nodes[0], &tmp, path->slots[0]);