Re: [syzbot] [btrfs?] general protection fault in btrfs_search_slot

[Lizhi Xu]

use the input logical can't find the extent root, so add sanity check for
extent root before search slot.

#syz test

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index f8e1d5b2c512..87eaf5dd2d5d 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -2213,6 +2213,9 @@ int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
 	key.objectid = logical;
 	key.offset = (u64)-1;
 
+	if (!extent_root)
+		return -ENOENT;
+
 	ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
 	if (ret < 0)
 		return ret;