system_path(): always return free'able memory to the caller

The function sometimes returns a newly allocated string and
sometimes returns a borrowed string, the latter of which the callers
must not free().  The existing callers all assume that the return
value belongs to the callee and most of them copy it with strdup()
when they want to keep it around.  They end up leaking the returned
copy when the callee returned a new string because they cannot tell
if they should free it.

Change the contract between the callers and system_path() to make
the returned string owned by the callers; they are responsible for
freeing it when done, but they do not have to make their own copy to
store it away.

Adjust the callers to make sure they do not leak the returned string
once they are done, but do not bother freeing it just before dying,
exiting or exec'ing other program to avoid unnecessary churn.

Reported-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/help.c

@@ -322,16 +322,18 @@ static void setup_man_path(void)
 {
 	struct strbuf new_path = STRBUF_INIT;
 	const char *old_path = getenv("MANPATH");
+	char *git_man_path = system_path(GIT_MAN_PATH);
 
 	/* We should always put ':' after our path. If there is no
 	 * old_path, the ':' at the end will let 'man' to try
 	 * system-wide paths after ours to find the manual page. If
 	 * there is old_path, we need ':' as delimiter. */
-	strbuf_addstr(&new_path, system_path(GIT_MAN_PATH));
+	strbuf_addstr(&new_path, git_man_path);
 	strbuf_addch(&new_path, ':');
 	if (old_path)
 		strbuf_addstr(&new_path, old_path);
 
+	free(git_man_path);
 	setenv("MANPATH", new_path.buf, 1);
 
 	strbuf_release(&new_path);
@@ -381,8 +383,10 @@ static void show_info_page(const char *git_cmd)
 static void get_html_page_path(struct strbuf *page_path, const char *page)
 {
 	struct stat st;
+	char *to_free = NULL;
+
 	if (!html_path)
-		html_path = system_path(GIT_HTML_PATH);
+		html_path = to_free = system_path(GIT_HTML_PATH);
 
 	/* Check that we have a git documentation directory. */
 	if (!strstr(html_path, "://")) {
@@ -393,6 +397,7 @@ static void get_html_page_path(struct strbuf *page_path, const char *page)
 
 	strbuf_init(page_path, 0);
 	strbuf_addf(page_path, "%s/%s.html", html_path, page);
+	free(to_free);
 }
 
 /*

builtin/init-db.c

@@ -119,15 +119,18 @@ static void copy_templates(const char *template_dir)
 	DIR *dir;
 	const char *git_dir = get_git_dir();
 	int len = strlen(git_dir);
+	char *to_free = NULL;
 
 	if (!template_dir)
 		template_dir = getenv(TEMPLATE_DIR_ENVIRONMENT);
 	if (!template_dir)
 		template_dir = init_db_template_dir;
 	if (!template_dir)
-		template_dir = system_path(DEFAULT_GIT_TEMPLATE_DIR);
-	if (!template_dir[0])
+		template_dir = to_free = system_path(DEFAULT_GIT_TEMPLATE_DIR);
+	if (!template_dir[0]) {
+		free(to_free);
 		return;
+	}
 	template_len = strlen(template_dir);
 	if (PATH_MAX <= (template_len+strlen("/config")))
 		die(_("insanely long template path %s"), template_dir);
@@ -139,7 +142,7 @@ static void copy_templates(const char *template_dir)
 	dir = opendir(template_path);
 	if (!dir) {
 		warning(_("templates not found %s"), template_dir);
-		return;
+		goto free_return;
 	}
 
 	/* Make sure that template is from the correct vintage */
@@ -155,8 +158,7 @@ static void copy_templates(const char *template_dir)
 			"a wrong format version %d from '%s'"),
 			repository_format_version,
 			template_dir);
-		closedir(dir);
-		return;
+		goto close_free_return;
 	}
 
 	memcpy(path, git_dir, len);
@@ -166,7 +168,10 @@ static void copy_templates(const char *template_dir)
 	copy_templates_1(path, len,
 			 template_path, template_len,
 			 dir);
+close_free_return:
 	closedir(dir);
+free_return:
+	free(to_free);
 }
 
 static int git_init_db_config(const char *k, const char *v, void *cb)

exec_cmd.c

@@ -6,7 +6,7 @@
 static const char *argv_exec_path;
 static const char *argv0_path;
 
-const char *system_path(const char *path)
+char *system_path(const char *path)
 {
 #ifdef RUNTIME_PREFIX
 	static const char *prefix;
@@ -16,7 +16,7 @@ const char *system_path(const char *path)
 	struct strbuf d = STRBUF_INIT;
 
 	if (is_absolute_path(path))
-		return path;
+		return xstrdup(path);
 
 #ifdef RUNTIME_PREFIX
 	assert(argv0_path);
@@ -34,8 +34,7 @@ const char *system_path(const char *path)
 #endif
 
 	strbuf_addf(&d, "%s/%s", prefix, path);
-	path = strbuf_detach(&d, NULL);
-	return path;
+	return strbuf_detach(&d, NULL);
 }
 
 const char *git_extract_argv0_path(const char *argv0)

exec_cmd.h

@@ -9,6 +9,6 @@ extern const char **prepare_git_cmd(const char **argv);
 extern int execv_git_cmd(const char **argv); /* NULL terminated */
 LAST_ARG_MUST_BE_NULL
 extern int execl_git_cmd(const char *cmd, ...);
-extern const char *system_path(const char *path);
+extern char *system_path(const char *path);
 
 #endif /* GIT_EXEC_CMD_H */