[PATCH] btrfs: fix a NULL pointer dereference

[Kangjie Lu]

btrfs_lookup_block_group may fail and return NULL. The fix goes
to out when it fails to avoid NULL pointer dereference.

Signed-off-by: Kangjie Lu <kjlu@xxxxxxx>
---
 fs/btrfs/extent-tree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 994f0cc41799..b1e7985bcb9d 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7303,6 +7303,8 @@ void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
 
 		pin = 0;
 		cache = btrfs_lookup_block_group(fs_info, buf->start);
+		if (!cache)
+			goto out;
 
 		if (btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN)) {
 			pin_down_extent(fs_info, cache, buf->start,
-- 
2.17.1