[PATCH] btrfs: Added null check to extent_root variable

[Ghanshyam Agrawal]

Reported-by: syzbot+9c3e0cdfbfe351b0bc0e@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes:https://syzkaller.appspot.com/bug?extid=9c3e0cdfbfe351b0bc0e
Signed-off-by: Ghanshyam Agrawal <ghanshyam1898@xxxxxxxxx>
---
 fs/btrfs/ref-verify.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/btrfs/ref-verify.c b/fs/btrfs/ref-verify.c
index 9522a8b79d22..4e98ddf5e8df 100644
--- a/fs/btrfs/ref-verify.c
+++ b/fs/btrfs/ref-verify.c
@@ -1002,6 +1002,9 @@ int btrfs_build_ref_tree(struct btrfs_fs_info *fs_info)
 		return -ENOMEM;
 
 	extent_root = btrfs_extent_root(fs_info, 0);
+	if (!extent_root)
+		return -EIO;
+
 	eb = btrfs_read_lock_root_node(extent_root);
 	level = btrfs_header_level(eb);
 	path->nodes[level] = eb;
-- 
2.34.1