[PATCH 2/2] scalar: free result of `remote_default_branch()`

From: Patrick Steinhardt <ps@pks.im>
Date: Jan 29, 2025, 16:24 UTC
Message-ID: <20250129-b4-pks-memory-leaks-v1-2-79e41299eb0c@pks.im>
In-Reply-To: <20250129-b4-pks-memory-leaks-v1-0-79e41299eb0c@pks.im>

We don't free the result of `remote_default_branch()`, leading to a memory leak. This leak is exposed by t9211, but only when run with Meson via `meson setup -Dsanitize=leak`:

    Direct leak of 5 byte(s) in 1 object(s) allocated from:
        #0 0x5555555cfb93 in malloc (scalar+0x7bb93)
        #1 0x5555556b05c2 in do_xmalloc ../wrapper.c:55:8
        #2 0x5555556b06c4 in do_xmallocz ../wrapper.c:89:8
        #3 0x5555556b0656 in xmallocz ../wrapper.c:97:9
        #4 0x5555556b0728 in xmemdupz ../wrapper.c:113:16
        #5 0x5555556b07a7 in xstrndup ../wrapper.c:119:9
        #6 0x5555555d3a4b in remote_default_branch ../scalar.c:338:14
        #7 0x5555555d20e6 in cmd_clone ../scalar.c:493:28
        #8 0x5555555d196b in cmd_main ../scalar.c:992:14
        #9 0x5555557c4059 in main ../common-main.c:64:11
        #10 0x7ffff7a2a1fb in __libc_start_call_main (/nix/store/h7zcxabfxa7v5xdna45y2hplj31ncf8a-glibc-2.40-36/lib/libc.so.6+0x2a1fb) (BuildId: 0a855678aa0cb573cecbb2bcc73ab8239ec472d0)
        #11 0x7ffff7a2a2b8 in __libc_start_main@GLIBC_2.2.5 (/nix/store/h7zcxabfxa7v5xdna45y2hplj31ncf8a-glibc-2.40-36/lib/libc.so.6+0x2a2b8) (BuildId: 0a855678aa0cb573cecbb2bcc73ab8239ec472d0)
        #12 0x555555592054 in _start (scalar+0x3e054)

    DEDUP_TOKEN: __interceptor_malloc--do_xmalloc--do_xmallocz--xmallocz--xmemdupz--xstrndup--remote_default_branch--cmd_clone--cmd_main--main--__libc_start_call_main--__libc_start_main@GLIBC_2.2.5--_start
    SUMMARY: LeakSanitizer: 5 byte(s) leaked in 1 allocation(s).

As the `branch` variable may contain a string constant obtained from parsing command line arguments we cannot free the leaking variable directly. Instead, introduce a new `branch_to_free` variable that only ever gets assigned the allocated string and free that one to plug the leak.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 scalar.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/scalar.c b/scalar.c
index f24bcd0169..da42b4be0c 100644
--- a/scalar.c
+++ b/scalar.c
@@ -409,6 +409,7 @@ void load_builtin_commands(const char *prefix UNUSED,
 static int cmd_clone(int argc, const char **argv)
 {
 	const char *branch = NULL;
+	char *branch_to_free = NULL;
 	int full_clone = 0, single_branch = 0, show_progress = isatty(2);
 	int src = 1, tags = 1;
 	struct option clone_options[] = {
@@ -490,7 +491,7 @@ static int cmd_clone(int argc, const char **argv)
 	/* common-main already logs `argv` */
 	trace2_def_repo(the_repository);
 
-	if (!branch && !(branch = remote_default_branch(url))) {
+	if (!branch && !(branch = branch_to_free = remote_default_branch(url))) {
 		res = error(_("failed to get default branch for '%s'"), url);
 		goto cleanup;
 	}
@@ -552,6 +553,7 @@ static int cmd_clone(int argc, const char **argv)
 	res = register_dir();
 
 cleanup:
+	free(branch_to_free);
 	free(enlistment);
 	free(dir);
 	strbuf_release(&buf);

-- 
2.48.1.362.g079036d154.dirty