Subject: Re: [PATCH] fmt-merge-msg: plug small leak of commit buffer

From: Jeff King <[email-masked]>
Date: Wed, 15 Apr 2015 18:14:32 -0400

On Wed, Apr 15, 2015 at 02:30:17PM -0700, Junio C Hamano wrote:

> I spoke too soon.  There are two error-exit paths in this function.
> 
> -- >8 --
> A broken or badly formatted commit might not record author or
> committer lines or we may not find a valid name on them.  The
> function record_person() returned after calling get_commit_buffer()
> without calling unuse_commit_buffer() on the memory it obtained in
> such cases, potentially leaking it.

Looks good. Thanks for cleaning my mess. I looked over the offending
bc6b8fc1, and the other changed spots all look OK.

I note that record_person does not seem to care about the commit at all,
so an alternative fix would be:

diff --git a/builtin/fmt-merge-msg.c b/builtin/fmt-merge-msg.c
index 1d962dc..9f0e608 100644
--- a/builtin/fmt-merge-msg.c
+++ b/builtin/fmt-merge-msg.c
@@ -223,16 +223,14 @@ static void add_branch_desc(struct strbuf *out, const char *name)
 
 #define util_as_integral(elem) ((intptr_t)((elem)->util))
 
-static void record_person(int which, struct string_list *people,
-			  struct commit *commit)
+static void record_person_from_buf(int which, struct string_list *people,
+				   const char *buffer)
 {
-	const char *buffer;
 	char *name_buf, *name, *name_end;
 	struct string_list_item *elem;
 	const char *field;
 
 	field = (which == 'a') ? "\nauthor " : "\ncommitter ";
-	buffer = get_commit_buffer(commit, NULL);
 	name = strstr(buffer, field);
 	if (!name)
 		return;
@@ -245,7 +243,6 @@ static void record_person(int which, struct string_list *people,
 	if (name_end < name)
 		return;
 	name_buf = xmemdupz(name, name_end - name + 1);
-	unuse_commit_buffer(commit, buffer);
 
 	elem = string_list_lookup(people, name_buf);
 	if (!elem) {
@@ -256,6 +253,14 @@ static void record_person(int which, struct string_list *people,
 	free(name_buf);
 }
 
+static void record_person(int which, struct string_list *people,
+			  struct commit *commit)
+{
+	const char *buf = get_commit_buffer(commit, NULL);
+	record_person_from_buf(which, people, buf);
+	unuse_commit_buffer(commit, buf);
+}
+
 static int cmp_string_list_util_as_integral(const void *a_, const void *b_)
 {
 	const struct string_list_item *a = a_, *b = b_;

This has the slight advantage that it adapts naturally if record_person
grows more exits, but I don't think it is a big deal either way (it only
matters if the new exit fails to copy the surrounding code and use "goto
leave").

-Peff