[PATCH 1/2] expand_user_path: do not look at NULL path

[Jeff King <peff@peff.net>]

We explicitly check for and handle the case that the
incoming "path" variable is NULL, but before doing so we
call strchrnul on it, leading to a potential segfault.

We can fix this simply by moving the strchrnul call down; as
a bonus, we can tighten the scope on the associated
variable.

Signed-off-by: Jeff King <peff@peff.net>
---
Most of the callers already check for NULL, so the only way to trigger
this is via an empty "include.path". That is addressed separately in the
next patch, so technically this is not needed if we apply that one. But
in that case, the "path == NULL" check here is useless, so I think this
makes things safer overall.

 path.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/path.c b/path.c
index 24594c4..f9c5062 100644
--- a/path.c
+++ b/path.c
@@ -265,12 +265,12 @@ static struct passwd *getpw_str(const char *username, size_t len)
 char *expand_user_path(const char *path)
 {
 	struct strbuf user_path = STRBUF_INIT;
-	const char *first_slash = strchrnul(path, '/');
 	const char *to_copy = path;
 
 	if (path == NULL)
 		goto return_null;
 	if (path[0] == '~') {
+		const char *first_slash = strchrnul(path, '/');
 		const char *username = path + 1;
 		size_t username_len = first_slash - username;
 		if (username_len == 0) {
-- 
1.8.5.2.500.g8060133