[PATCH 4.9 023/151] btrfs: handle error of get_old_root

[Greg Kroah-Hartman]

From: Nikolay Borisov <nborisov@xxxxxxxx>

[ Upstream commit 315bed43fea532650933e7bba316a7601d439edf ]

In btrfs_search_old_slot get_old_root is always used with the assumption
it cannot fail. However, this is not true in rare circumstance it can
fail and return null. This will lead to null point dereference when the
header is read. Fix this by checking the return value and properly
handling NULL by setting ret to -EIO and returning gracefully.

Coverity-id: 1087503
Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
Reviewed-by: Lu Fengqi <lufq.fnst@xxxxxxxxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/btrfs/ctree.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 3df434eb14743..3faccbf35e9f4 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -2973,6 +2973,10 @@ int btrfs_search_old_slot(struct btrfs_root *root, struct btrfs_key *key,
 
 again:
 	b = get_old_root(root, time_seq);
+	if (!b) {
+		ret = -EIO;
+		goto done;
+	}
 	level = btrfs_header_level(b);
 	p->locks[level] = BTRFS_READ_LOCK;
 
-- 
2.20.1