prefer git_pathdup to git_path in some possibly-dangerous cases

Because git_path uses a static buffer that is shared with
calls to git_path, mkpath, etc, it can be dangerous to
assign the result to a variable or pass it to a non-trivial
function. The value may change unexpectedly due to other
calls.

None of the cases changed here has a known bug, but they're
worth converting away from git_path because:

  1. It's easy to use git_pathdup in these cases.

  2. They use constructs (like assignment) that make it
     hard to tell whether they're safe or not.

The extra malloc overhead should be trivial, as an
allocation should be an order of magnitude cheaper than a
system call (which we are clearly about to make, since we
are constructing a filename). The real cost is that we must
remember to free the result.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 6 deletions

diff --git a/refs.c b/refs.c
index 2db2975e08..93b250e754 100644
--- a/refs.c
+++ b/refs.c
@@ -1288,12 +1288,12 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir)
  */
 static struct packed_ref_cache *get_packed_ref_cache(struct ref_cache *refs)
 {
-	const char *packed_refs_file;
+	char *packed_refs_file;
 
 	if (*refs->name)
-		packed_refs_file = git_path_submodule(refs->name, "packed-refs");
+		packed_refs_file = git_pathdup_submodule(refs->name, "packed-refs");
 	else
-		packed_refs_file = git_path("packed-refs");
+		packed_refs_file = git_pathdup("packed-refs");
 
 	if (refs->packed &&
 	    !stat_validity_check(&refs->packed->validity, packed_refs_file))
@@ -1312,6 +1312,7 @@ static struct packed_ref_cache *get_packed_ref_cache(struct ref_cache *refs)
 			fclose(f);
 		}
 	}
+	free(packed_refs_file);
 	return refs->packed;
 }
 
@@ -1481,14 +1482,15 @@ static int resolve_gitlink_ref_recursive(struct ref_cache *refs,
 {
 	int fd, len;
 	char buffer[128], *p;
-	const char *path;
+	char *path;
 
 	if (recursion > MAXDEPTH || strlen(refname) > MAXREFLEN)
 		return -1;
 	path = *refs->name
-		? git_path_submodule(refs->name, "%s", refname)
-		: git_path("%s", refname);
+		? git_pathdup_submodule(refs->name, "%s", refname)
+		: git_pathdup("%s", refname);
 	fd = open(path, O_RDONLY);
+	free(path);
 	if (fd < 0)
 		return resolve_gitlink_packed_ref(refs, refname, sha1);