[PATCH] fs: kernfs: fix possible null pointer dereferences

[youngjun]

kernfs_path_from_node_locked checks buf is NULL.
But, two cases below are not covered.

if(!kn_to)			<--- case1 (buf can be NULL)
	return strlcpy(buf, "(null)", buflen);

if(kn_from == kn_to)		<--- case2 (buf can be NULL)
	return strlcpy(buf, "/", buflen);

if (!buf)			<--- checked here.
	return -EINVAL;

buf NULL case needs to be checked first.

Signed-off-by: youngjun <her0gyugyu@xxxxxxxxx>
---
 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 02fb5cc76e33..d802cfceddba 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -128,6 +128,9 @@ 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);
 
@@ -137,9 +140,6 @@ 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;
-- 
2.17.1