bpf: fix bpf_d_path() helper prototype

kernel/trace/bpf_trace.c

@@ -965,7 +965,7 @@ static const struct bpf_func_proto bpf_d_path_proto = {
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_PTR_TO_BTF_ID,
 	.arg1_btf_id	= &bpf_d_path_btf_ids[0],
-	.arg2_type	= ARG_PTR_TO_MEM,
+	.arg2_type	= ARG_PTR_TO_MEM | MEM_WRITE,
 	.arg3_type	= ARG_CONST_SIZE_OR_ZERO,
 	.allowed	= bpf_d_path_allowed,
 };

tools/testing/selftests/bpf/prog_tests/d_path.c

@@ -195,6 +195,67 @@ static void test_d_path_check_types(void)
 	test_d_path_check_types__destroy(skel);
 }
 
+static void test_d_path_lsm(void)
+{
+	struct test_d_path *skel;
+	int err;
+	int pipefd[2];
+	pid_t pid;
+
+	skel = test_d_path__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "d_path skeleton failed"))
+		return;
+
+	err = test_d_path__attach(skel);
+	if (!ASSERT_OK(err, "attach failed"))
+		goto cleanup;
+
+	/* Prepare the test binary */
+	system("cp /bin/true /tmp/bpf_d_path_test 2>/dev/null || :");
+
+	if (!ASSERT_OK(pipe(pipefd), "pipe failed"))
+		goto cleanup;
+
+	pid = fork();
+	if (!ASSERT_GE(pid, 0, "fork failed")) {
+		close(pipefd[0]);
+		close(pipefd[1]);
+		goto cleanup;
+	}
+
+	if (pid == 0) {
+		/* Child */
+		char buf;
+
+		close(pipefd[1]);
+		/* Wait for parent to set PID in BPF map */
+		if (read(pipefd[0], &buf, 1) != 1)
+			exit(1);
+		close(pipefd[0]);
+		execl("/tmp/bpf_d_path_test", "/tmp/bpf_d_path_test", NULL);
+		exit(1);
+	}
+
+	/* Parent */
+	close(pipefd[0]);
+
+	/* Update BPF map with child PID */
+	skel->bss->my_pid = pid;
+
+	/* Signal child to proceed */
+	write(pipefd[1], "G", 1);
+	close(pipefd[1]);
+
+	/* Wait for child */
+	waitpid(pid, NULL, 0);
+
+	ASSERT_EQ(skel->bss->called_lsm, 1, "lsm hook called");
+	ASSERT_EQ(skel->bss->lsm_match, 1, "lsm match");
+
+cleanup:
+	test_d_path__destroy(skel);
+}
+
 void test_d_path(void)
 {
 	if (test__start_subtest("basic"))
@@ -205,4 +266,7 @@ void test_d_path(void)
 
 	if (test__start_subtest("check_alloc_mem"))
 		test_d_path_check_types();
+
+	if (test__start_subtest("lsm"))
+		test_d_path_lsm();
 }

tools/testing/selftests/bpf/progs/test_d_path.c

@@ -17,6 +17,8 @@ int rets_close[MAX_FILES] = {};
 
 int called_stat = 0;
 int called_close = 0;
+int called_lsm = 0;
+int lsm_match = 0;
 
 SEC("fentry/security_inode_getattr")
 int BPF_PROG(prog_stat, struct path *path, struct kstat *stat,
@@ -62,4 +64,35 @@ int BPF_PROG(prog_close, struct file *file, void *id)
 	return 0;
 }
 
+SEC("lsm/bprm_check_security")
+int BPF_PROG(prog_lsm, struct linux_binprm *bprm)
+{
+	pid_t pid = bpf_get_current_pid_tgid() >> 32;
+	char path[MAX_PATH_LEN] = {};
+	int ret;
+
+	if (pid != my_pid)
+		return 0;
+
+	called_lsm = 1;
+	ret = bpf_d_path(&bprm->file->f_path, path, MAX_PATH_LEN);
+	if (ret < 0)
+		return 0;
+
+	{
+		static const char target_dir[] = "/tmp/";
+
+#pragma unroll
+		for (int i = 0; i < sizeof(target_dir) - 1; i++) {
+			if (path[i] != target_dir[i]) {
+				lsm_match = -1; /* mismatch */
+				return 0;
+			}
+		}
+	}
+
+	lsm_match = 1; /* prefix match */
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";