selftests/xattr: sockfs socket xattr tests

Test user.* extended attribute operations on sockfs sockets. Sockets
created via socket() have their inodes in sockfs, which now supports
user.* xattrs with per-inode limits.

Tests fsetxattr/fgetxattr/flistxattr/fremovexattr operations including
set/get, listing (verifies system.sockprotoname presence), remove,
update, XATTR_CREATE/XATTR_REPLACE flags, empty values, size queries,
and buffer-too-small errors.

Also tests per-inode limit enforcement: maximum 128 xattrs, maximum
128KB total value size, limit recovery after removal, and independent
limits across different sockets.

Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-13-c2efa4f74cb7@kernel.org
Acked-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

tools/testing/selftests/filesystems/xattr/.gitignore

@@ -1 +1,2 @@
 xattr_socket_test
+xattr_sockfs_test

tools/testing/selftests/filesystems/xattr/Makefile

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 
 CFLAGS += $(KHDR_INCLUDES)
-TEST_GEN_PROGS := xattr_socket_test
+TEST_GEN_PROGS := xattr_socket_test xattr_sockfs_test
 
 include ../../lib.mk

tools/testing/selftests/filesystems/xattr/xattr_sockfs_test.c

@@ -0,0 +1,363 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2026 Christian Brauner <brauner@kernel.org>
+/*
+ * Test extended attributes on sockfs sockets.
+ *
+ * Sockets created via socket() have their inodes in sockfs, which supports
+ * user.* xattrs with per-inode limits: up to 128 xattrs and 128KB total
+ * value size. These tests verify xattr operations via fsetxattr/fgetxattr/
+ * flistxattr/fremovexattr on the socket fd, as well as limit enforcement.
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/xattr.h>
+#include <unistd.h>
+
+#include "../../kselftest_harness.h"
+
+#define TEST_XATTR_NAME		"user.testattr"
+#define TEST_XATTR_VALUE	"testvalue"
+#define TEST_XATTR_VALUE2	"newvalue"
+
+/* Per-inode limits for user.* xattrs on sockfs (from include/linux/xattr.h) */
+#define SIMPLE_XATTR_MAX_NR	128
+#define SIMPLE_XATTR_MAX_SIZE	(128 << 10)	/* 128 KB */
+
+#ifndef XATTR_SIZE_MAX
+#define XATTR_SIZE_MAX 65536
+#endif
+
+/*
+ * Fixture for sockfs socket xattr tests.
+ * Creates an AF_UNIX socket (lives in sockfs, not bound to any path).
+ */
+FIXTURE(xattr_sockfs)
+{
+	int sockfd;
+};
+
+FIXTURE_SETUP(xattr_sockfs)
+{
+	self->sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
+	ASSERT_GE(self->sockfd, 0) {
+		TH_LOG("Failed to create socket: %s", strerror(errno));
+	}
+}
+
+FIXTURE_TEARDOWN(xattr_sockfs)
+{
+	if (self->sockfd >= 0)
+		close(self->sockfd);
+}
+
+TEST_F(xattr_sockfs, set_get_user_xattr)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("fsetxattr failed: %s", strerror(errno));
+	}
+
+	memset(buf, 0, sizeof(buf));
+	ret = fgetxattr(self->sockfd, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, (ssize_t)strlen(TEST_XATTR_VALUE)) {
+		TH_LOG("fgetxattr returned %zd: %s", ret, strerror(errno));
+	}
+	ASSERT_STREQ(buf, TEST_XATTR_VALUE);
+}
+
+/*
+ * Test listing xattrs on a sockfs socket.
+ * Should include user.* xattrs and system.sockprotoname.
+ */
+TEST_F(xattr_sockfs, list_user_xattr)
+{
+	char list[4096];
+	ssize_t ret;
+	char *ptr;
+	bool found_user = false;
+	bool found_proto = false;
+
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("fsetxattr failed: %s", strerror(errno));
+	}
+
+	memset(list, 0, sizeof(list));
+	ret = flistxattr(self->sockfd, list, sizeof(list));
+	ASSERT_GT(ret, 0) {
+		TH_LOG("flistxattr failed: %s", strerror(errno));
+	}
+
+	for (ptr = list; ptr < list + ret; ptr += strlen(ptr) + 1) {
+		if (strcmp(ptr, TEST_XATTR_NAME) == 0)
+			found_user = true;
+		if (strcmp(ptr, "system.sockprotoname") == 0)
+			found_proto = true;
+	}
+	ASSERT_TRUE(found_user) {
+		TH_LOG("user xattr not found in list");
+	}
+	ASSERT_TRUE(found_proto) {
+		TH_LOG("system.sockprotoname not found in list");
+	}
+}
+
+TEST_F(xattr_sockfs, remove_user_xattr)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = fremovexattr(self->sockfd, TEST_XATTR_NAME);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("fremovexattr failed: %s", strerror(errno));
+	}
+
+	ret = fgetxattr(self->sockfd, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENODATA);
+}
+
+TEST_F(xattr_sockfs, update_user_xattr)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE2, strlen(TEST_XATTR_VALUE2), 0);
+	ASSERT_EQ(ret, 0);
+
+	memset(buf, 0, sizeof(buf));
+	ret = fgetxattr(self->sockfd, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, (ssize_t)strlen(TEST_XATTR_VALUE2));
+	ASSERT_STREQ(buf, TEST_XATTR_VALUE2);
+}
+
+TEST_F(xattr_sockfs, xattr_create_flag)
+{
+	int ret;
+
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE2, strlen(TEST_XATTR_VALUE2),
+			XATTR_CREATE);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, EEXIST);
+}
+
+TEST_F(xattr_sockfs, xattr_replace_flag)
+{
+	int ret;
+
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE),
+			XATTR_REPLACE);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENODATA);
+}
+
+TEST_F(xattr_sockfs, get_nonexistent)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = fgetxattr(self->sockfd, "user.nonexistent", buf, sizeof(buf));
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENODATA);
+}
+
+TEST_F(xattr_sockfs, empty_value)
+{
+	ssize_t ret;
+
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME, "", 0, 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = fgetxattr(self->sockfd, TEST_XATTR_NAME, NULL, 0);
+	ASSERT_EQ(ret, 0);
+}
+
+TEST_F(xattr_sockfs, get_size)
+{
+	ssize_t ret;
+
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = fgetxattr(self->sockfd, TEST_XATTR_NAME, NULL, 0);
+	ASSERT_EQ(ret, (ssize_t)strlen(TEST_XATTR_VALUE));
+}
+
+TEST_F(xattr_sockfs, buffer_too_small)
+{
+	char buf[2];
+	ssize_t ret;
+
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = fgetxattr(self->sockfd, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ERANGE);
+}
+
+/*
+ * Test maximum number of user.* xattrs per socket.
+ * The kernel enforces SIMPLE_XATTR_MAX_NR (128), so the 129th should
+ * fail with ENOSPC.
+ */
+TEST_F(xattr_sockfs, max_nr_xattrs)
+{
+	char name[32];
+	int i, ret;
+
+	for (i = 0; i < SIMPLE_XATTR_MAX_NR; i++) {
+		snprintf(name, sizeof(name), "user.test%03d", i);
+		ret = fsetxattr(self->sockfd, name, "v", 1, 0);
+		ASSERT_EQ(ret, 0) {
+			TH_LOG("fsetxattr %s failed at i=%d: %s",
+			       name, i, strerror(errno));
+		}
+	}
+
+	ret = fsetxattr(self->sockfd, "user.overflow", "v", 1, 0);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENOSPC) {
+		TH_LOG("Expected ENOSPC for xattr %d, got %s",
+		       SIMPLE_XATTR_MAX_NR + 1, strerror(errno));
+	}
+}
+
+/*
+ * Test maximum total value size for user.* xattrs.
+ * The kernel enforces SIMPLE_XATTR_MAX_SIZE (128KB). Individual xattr
+ * values are limited to XATTR_SIZE_MAX (64KB) by the VFS, so we need
+ * at least two xattrs to hit the total limit.
+ */
+TEST_F(xattr_sockfs, max_xattr_size)
+{
+	char *value;
+	int ret;
+
+	value = malloc(XATTR_SIZE_MAX);
+	ASSERT_NE(value, NULL);
+	memset(value, 'A', XATTR_SIZE_MAX);
+
+	/* First 64KB xattr - total = 64KB */
+	ret = fsetxattr(self->sockfd, "user.big1", value, XATTR_SIZE_MAX, 0);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("first large xattr failed: %s", strerror(errno));
+	}
+
+	/* Second 64KB xattr - total = 128KB (exactly at limit) */
+	ret = fsetxattr(self->sockfd, "user.big2", value, XATTR_SIZE_MAX, 0);
+	free(value);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("second large xattr failed: %s", strerror(errno));
+	}
+
+	/* Third xattr with 1 byte - total > 128KB, should fail */
+	ret = fsetxattr(self->sockfd, "user.big3", "v", 1, 0);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENOSPC) {
+		TH_LOG("Expected ENOSPC when exceeding size limit, got %s",
+		       strerror(errno));
+	}
+}
+
+/*
+ * Test that removing an xattr frees limit space, allowing re-addition.
+ */
+TEST_F(xattr_sockfs, limit_remove_readd)
+{
+	char name[32];
+	int i, ret;
+
+	/* Fill up to the maximum count */
+	for (i = 0; i < SIMPLE_XATTR_MAX_NR; i++) {
+		snprintf(name, sizeof(name), "user.test%03d", i);
+		ret = fsetxattr(self->sockfd, name, "v", 1, 0);
+		ASSERT_EQ(ret, 0);
+	}
+
+	/* Verify we're at the limit */
+	ret = fsetxattr(self->sockfd, "user.overflow", "v", 1, 0);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENOSPC);
+
+	/* Remove one xattr */
+	ret = fremovexattr(self->sockfd, "user.test000");
+	ASSERT_EQ(ret, 0);
+
+	/* Now we should be able to add one more */
+	ret = fsetxattr(self->sockfd, "user.newattr", "v", 1, 0);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("re-add after remove failed: %s", strerror(errno));
+	}
+}
+
+/*
+ * Test that two different sockets have independent xattr limits.
+ */
+TEST_F(xattr_sockfs, limits_per_inode)
+{
+	char buf[256];
+	int sock2;
+	ssize_t ret;
+
+	sock2 = socket(AF_UNIX, SOCK_STREAM, 0);
+	ASSERT_GE(sock2, 0);
+
+	/* Set xattr on first socket */
+	ret = fsetxattr(self->sockfd, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0);
+
+	/* First socket's xattr should not be visible on second socket */
+	ret = fgetxattr(sock2, TEST_XATTR_NAME, NULL, 0);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENODATA);
+
+	/* Second socket should independently accept xattrs */
+	ret = fsetxattr(sock2, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE2, strlen(TEST_XATTR_VALUE2), 0);
+	ASSERT_EQ(ret, 0);
+
+	/* Verify each socket has its own value */
+	memset(buf, 0, sizeof(buf));
+	ret = fgetxattr(self->sockfd, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, (ssize_t)strlen(TEST_XATTR_VALUE));
+	ASSERT_STREQ(buf, TEST_XATTR_VALUE);
+
+	memset(buf, 0, sizeof(buf));
+	ret = fgetxattr(sock2, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, (ssize_t)strlen(TEST_XATTR_VALUE2));
+	ASSERT_STREQ(buf, TEST_XATTR_VALUE2);
+
+	close(sock2);
+}
+
+TEST_HARNESS_MAIN