selftests/pidfd: test setattr support

Verify that ->setattr() on a pidfd doens't work.

Link: https://lore.kernel.org/20250618-work-pidfs-persistent-v2-15-98f3456fd552@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

tools/testing/selftests/pidfd/.gitignore

@@ -11,3 +11,4 @@ pidfd_bind_mount
 pidfd_info_test
 pidfd_exec_helper
 pidfd_xattr_test
+pidfd_setattr_test

tools/testing/selftests/pidfd/Makefile

@@ -4,7 +4,7 @@ CFLAGS += -g $(KHDR_INCLUDES) -pthread -Wall
 TEST_GEN_PROGS := pidfd_test pidfd_fdinfo_test pidfd_open_test \
 	pidfd_poll_test pidfd_wait pidfd_getfd_test pidfd_setns_test \
 	pidfd_file_handle_test pidfd_bind_mount pidfd_info_test \
-	pidfd_xattr_test
+	pidfd_xattr_test pidfd_setattr_test
 
 TEST_GEN_PROGS_EXTENDED := pidfd_exec_helper
 

tools/testing/selftests/pidfd/pidfd_setattr_test.c

@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <linux/types.h>
+#include <poll.h>
+#include <pthread.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syscall.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <linux/kcmp.h>
+#include <sys/stat.h>
+#include <sys/xattr.h>
+
+#include "pidfd.h"
+#include "../kselftest_harness.h"
+
+FIXTURE(pidfs_setattr)
+{
+	pid_t child_pid;
+	int child_pidfd;
+};
+
+FIXTURE_SETUP(pidfs_setattr)
+{
+	self->child_pid = create_child(&self->child_pidfd, CLONE_NEWUSER | CLONE_NEWPID);
+	EXPECT_GE(self->child_pid, 0);
+
+	if (self->child_pid == 0)
+		_exit(EXIT_SUCCESS);
+}
+
+FIXTURE_TEARDOWN(pidfs_setattr)
+{
+	sys_waitid(P_PID, self->child_pid, NULL, WEXITED);
+	EXPECT_EQ(close(self->child_pidfd), 0);
+}
+
+TEST_F(pidfs_setattr, no_chown)
+{
+	ASSERT_LT(fchown(self->child_pidfd, 1234, 5678), 0);
+	ASSERT_EQ(errno, EOPNOTSUPP);
+}
+
+TEST_F(pidfs_setattr, no_chmod)
+{
+	ASSERT_LT(fchmod(self->child_pidfd, 0777), 0);
+	ASSERT_EQ(errno, EOPNOTSUPP);
+}
+
+TEST_F(pidfs_setattr, no_exec)
+{
+	char *const argv[] = { NULL };
+	char *const envp[] = { NULL };
+
+	ASSERT_LT(execveat(self->child_pidfd, "", argv, envp, AT_EMPTY_PATH), 0);
+	ASSERT_EQ(errno, EACCES);
+}
+
+TEST_HARNESS_MAIN