diffcore-order: fix leaking buffer when parsing orderfiles

In `prepare_order()` we parse an orderfile and assign it to a global
array. In order to save on some allocations, we replace newlines with
NUL characters and then assign pointers into the allocated buffer to
that array. This can cause the buffer to be completely unreferenced
though in some cases, e.g. because the order file is empty or because we
had to use `xmemdupz()` to copy the lines instead of NUL-terminating
them.

Refactor the code to always `xmemdupz()` the strings. This is a bit
simpler, and it is rather unlikely that saving a handful of allocations
really matters. This allows us to release the string buffer and thus
plug the memory leak.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

diffcore-order.c

@@ -14,8 +14,7 @@ static void prepare_order(const char *orderfile)
 {
 	int cnt, pass;
 	struct strbuf sb = STRBUF_INIT;
-	void *map;
-	char *cp, *endp;
+	const char *cp, *endp;
 	ssize_t sz;
 
 	if (order)
@@ -24,14 +23,13 @@ static void prepare_order(const char *orderfile)
 	sz = strbuf_read_file(&sb, orderfile, 0);
 	if (sz < 0)
 		die_errno(_("failed to read orderfile '%s'"), orderfile);
-	map = strbuf_detach(&sb, NULL);
-	endp = (char *) map + sz;
+	endp = sb.buf + sz;
 
 	for (pass = 0; pass < 2; pass++) {
 		cnt = 0;
-		cp = map;
+		cp = sb.buf;
 		while (cp < endp) {
-			char *ep;
+			const char *ep;
 			for (ep = cp; ep < endp && *ep != '\n'; ep++)
 				;
 			/* cp to ep has one line */
@@ -40,12 +38,7 @@ static void prepare_order(const char *orderfile)
 			else if (pass == 0)
 				cnt++;
 			else {
-				if (*ep == '\n') {
-					*ep = 0;
-					order[cnt] = cp;
-				} else {
-					order[cnt] = xmemdupz(cp, ep - cp);
-				}
+				order[cnt] = xmemdupz(cp, ep - cp);
 				cnt++;
 			}
 			if (ep < endp)
@@ -57,6 +50,8 @@ static void prepare_order(const char *orderfile)
 			ALLOC_ARRAY(order, cnt);
 		}
 	}
+
+	strbuf_release(&sb);
 }
 
 static int match_order(const char *path)

t/t4056-diff-order.sh

@@ -5,6 +5,7 @@ test_description='diff order & rotate'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 create_files () {

t/t4204-patch-id.sh

@@ -5,6 +5,7 @@ test_description='git patch-id'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success 'setup' '