selftests/pidfd: test extended attribute support

Add tests for extended attribute support on pidfds.

Link: https://lore.kernel.org/20250618-work-pidfs-persistent-v2-13-98f3456fd552@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

@@ -10,3 +10,4 @@ pidfd_file_handle_test
 pidfd_bind_mount
 pidfd_info_test
 pidfd_exec_helper
+pidfd_xattr_test

tools/testing/selftests/pidfd/Makefile

@@ -3,7 +3,8 @@ 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_file_handle_test pidfd_bind_mount pidfd_info_test \
+	pidfd_xattr_test
 
 TEST_GEN_PROGS_EXTENDED := pidfd_exec_helper
 

tools/testing/selftests/pidfd/pidfd_xattr_test.c

@@ -0,0 +1,97 @@
+// 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_xattr)
+{
+	pid_t child_pid;
+	int child_pidfd;
+};
+
+FIXTURE_SETUP(pidfs_xattr)
+{
+	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_xattr)
+{
+	sys_waitid(P_PID, self->child_pid, NULL, WEXITED);
+}
+
+TEST_F(pidfs_xattr, set_get_list_xattr_multiple)
+{
+	int ret, i;
+	char xattr_name[32];
+	char xattr_value[32];
+	char buf[32];
+	const int num_xattrs = 10;
+	char list[PATH_MAX] = {};
+
+	for (i = 0; i < num_xattrs; i++) {
+		snprintf(xattr_name, sizeof(xattr_name), "trusted.testattr%d", i);
+		snprintf(xattr_value, sizeof(xattr_value), "testvalue%d", i);
+		ret = fsetxattr(self->child_pidfd, xattr_name, xattr_value, strlen(xattr_value), 0);
+		ASSERT_EQ(ret, 0);
+	}
+
+	for (i = 0; i < num_xattrs; i++) {
+		snprintf(xattr_name, sizeof(xattr_name), "trusted.testattr%d", i);
+		snprintf(xattr_value, sizeof(xattr_value), "testvalue%d", i);
+		memset(buf, 0, sizeof(buf));
+		ret = fgetxattr(self->child_pidfd, xattr_name, buf, sizeof(buf));
+		ASSERT_EQ(ret, strlen(xattr_value));
+		ASSERT_EQ(strcmp(buf, xattr_value), 0);
+	}
+
+	ret = flistxattr(self->child_pidfd, list, sizeof(list));
+	ASSERT_GT(ret, 0);
+	for (i = 0; i < num_xattrs; i++) {
+		snprintf(xattr_name, sizeof(xattr_name), "trusted.testattr%d", i);
+		bool found = false;
+		for (char *it = list; it < list + ret; it += strlen(it) + 1) {
+			if (strcmp(it, xattr_name))
+				continue;
+			found = true;
+			break;
+		}
+		ASSERT_TRUE(found);
+	}
+
+	for (i = 0; i < num_xattrs; i++) {
+		snprintf(xattr_name, sizeof(xattr_name), "trusted.testattr%d", i);
+		ret = fremovexattr(self->child_pidfd, xattr_name);
+		ASSERT_EQ(ret, 0);
+
+		ret = fgetxattr(self->child_pidfd, xattr_name, buf, sizeof(buf));
+		ASSERT_EQ(ret, -1);
+		ASSERT_EQ(errno, ENODATA);
+	}
+}
+
+TEST_HARNESS_MAIN