[PATCH] btrfs: add a sanity check for btrfs root

[Lizhi Xu]

Syzbot report a null-ptr-deref in btrfs_search_slot.
It use the input logical can't find the extent root in extent_from_logical,
and triger the null-ptr-deref in btrfs_search_slot.
Add sanity check for btrfs root before using it in btrfs_search_slot.

Reported-by: syzbot+3030e17bd57a73d39bd7@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=3030e17bd57a73d39bd7
Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
---
 fs/btrfs/ctree.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 0cc919d15b14..9c05cab473f5 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -2010,7 +2010,7 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		      const struct btrfs_key *key, struct btrfs_path *p,
 		      int ins_len, int cow)
 {
-	struct btrfs_fs_info *fs_info = root->fs_info;
+	struct btrfs_fs_info *fs_info;
 	struct extent_buffer *b;
 	int slot;
 	int ret;
@@ -2023,6 +2023,10 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 	int min_write_lock_level;
 	int prev_cmp;
 
+	if (!root)
+		return -EINVAL;
+
+	fs_info = root->fs_info;
 	might_sleep();
 
 	lowest_level = p->lowest_level;
-- 
2.43.0