fs: Fix link_path_walk to return -ENOENT on empty path

link_path_walk was returning 0 when passed with an empty path,
this lead calling code to assume that the struct nameidata nd
is valid and thus has a `last` field populated, which is not.
In the end causing a runtime crash.

This issue can easily be reproduced by running the command:
cat ""

Reported-by: Neeraj Pal <neerajpal09@gmail.com>
Signed-off-by: Jules Maselbas <jmaselbas@kalray.eu>
Link: https://lore.barebox.org/20210417233409.637-1-jmaselbas@kalray.eu
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/fs.c b/fs/fs.c
index a023324913..6de5a3b59e 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -1928,6 +1928,8 @@ static int link_path_walk(const char *name, struct nameidata *nd)
 	int err;
 	char separator = '/';
 
+	if (!*name)
+		return -ENOENT;
 	while (*name=='/')
 		name++;
 	if (!*name)