[PATCH] kernfs: fix potential null-ptr-deref in kernfs_path_from_node_locked()

[Zhen Lei <thunder.leizhen@huawei.com>]

Ensure that the 'buf' is not empty before strlcpy() uses it.

Commit bbe70e4e4211 ("fs: kernfs: Fix possible null-pointer dereferences
in kernfs_path_from_node_locked()") first noticed this, but it didn't
fix it completely.

Fixes: 9f6df573a404 ("kernfs: Add API to generate relative kernfs path")
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 fs/kernfs/dir.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index f33b3baad07cb36..b2422265c86edf2 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -140,6 +140,9 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
 	size_t depth_from, depth_to, len = 0;
 	int i, j;
 
+	if (!buf)
+		return -EINVAL;
+
 	if (!kn_to)
 		return strlcpy(buf, "(null)", buflen);
 
@@ -149,9 +152,6 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
 	if (kn_from == kn_to)
 		return strlcpy(buf, "/", buflen);
 
-	if (!buf)
-		return -EINVAL;
-
 	common = kernfs_common_ancestor(kn_from, kn_to);
 	if (WARN_ON(!common))
 		return -EINVAL;
-- 
2.25.1