Fix underflow in path_remove_trailing()

src/emu/path.c

@@ -96,7 +96,7 @@ void
 path_remove_trailing(char *path)
 {
 	int n = strlen(path);
-	for (int i = n - 1; path[i] == '/'; i--) {
+	for (int i = n - 1; i >= 0 && path[i] == '/'; i--) {
 		path[i] = '\0';
 	}
 }

test/unit/CMakeLists.txt

@@ -14,3 +14,4 @@ unit_test(stream.c)
 unit_test(thread.c)
 unit_test(value.c)
 unit_test(version.c)
+unit_test(path.c)

test/unit/path.c

@@ -0,0 +1,35 @@
+/* Copyright (c) 2023 Barcelona Supercomputing Center (BSC)
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include "emu/path.h"
+#include "common.h"
+#include <string.h>
+
+static void
+test_underflow_trailing(void)
+{
+	char in[]  = { 'A', '/', '/', '/', '/', '\0', 'B' };
+	char out[] = { 'A', '/', '\0','\0','\0','\0', 'B' };
+	char *p = in + 2; /*      ^here */
+
+	path_remove_trailing(p);
+
+	if (memcmp(in, out, sizeof(in)) != 0) {
+		for (size_t i = 0; i < sizeof(in); i++) {
+			err("i=%3d, in[i]=%02x out[i]=%02x\n", i,
+					(unsigned char) in[i],
+					(unsigned char) out[i]);
+		}
+		die("path mismatch");
+	}
+
+	err("OK\n");
+}
+
+int
+main(void)
+{
+	test_underflow_trailing();
+
+	return 0;
+}