selftests/xattr: test xattrs on various socket families

Test user.* xattr operations on sockets from different address families:
AF_INET, AF_INET6, AF_NETLINK, and AF_PACKET. All socket types use
sockfs for their inodes, so user.* xattrs should work regardless of
address family.

Each fixture creates a socket (no bind needed) and verifies the full
fsetxattr/fgetxattr/flistxattr/fremovexattr cycle. AF_INET6 skips if
not supported; AF_PACKET skips if CAP_NET_RAW is unavailable.

Also tests abstract namespace AF_UNIX sockets, which live in sockfs
(not on a filesystem) and should support user.* xattrs.

Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-14-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>

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

@@ -1,2 +1,3 @@
 xattr_socket_test
 xattr_sockfs_test
+xattr_socket_types_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 xattr_sockfs_test
+TEST_GEN_PROGS := xattr_socket_test xattr_sockfs_test xattr_socket_types_test
 
 include ../../lib.mk

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

@@ -0,0 +1,177 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2026 Christian Brauner <brauner@kernel.org>
+/*
+ * Test user.* xattrs on various socket families.
+ *
+ * All socket types use sockfs for their inodes, so user.* xattrs should
+ * work on any socket regardless of address family. This tests AF_INET,
+ * AF_INET6, AF_NETLINK, AF_PACKET, and abstract namespace AF_UNIX sockets.
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/un.h>
+#include <sys/xattr.h>
+#include <linux/netlink.h>
+#include <unistd.h>
+
+#include "../../kselftest_harness.h"
+
+#define TEST_XATTR_NAME		"user.testattr"
+#define TEST_XATTR_VALUE	"testvalue"
+
+FIXTURE(xattr_socket_types)
+{
+	int sockfd;
+};
+
+FIXTURE_VARIANT(xattr_socket_types)
+{
+	int family;
+	int type;
+	int protocol;
+};
+
+FIXTURE_VARIANT_ADD(xattr_socket_types, inet) {
+	.family = AF_INET,
+	.type = SOCK_STREAM,
+	.protocol = 0,
+};
+
+FIXTURE_VARIANT_ADD(xattr_socket_types, inet6) {
+	.family = AF_INET6,
+	.type = SOCK_STREAM,
+	.protocol = 0,
+};
+
+FIXTURE_VARIANT_ADD(xattr_socket_types, netlink) {
+	.family = AF_NETLINK,
+	.type = SOCK_RAW,
+	.protocol = NETLINK_USERSOCK,
+};
+
+FIXTURE_VARIANT_ADD(xattr_socket_types, packet) {
+	.family = AF_PACKET,
+	.type = SOCK_DGRAM,
+	.protocol = 0,
+};
+
+FIXTURE_SETUP(xattr_socket_types)
+{
+	self->sockfd = socket(variant->family, variant->type,
+			      variant->protocol);
+	if (self->sockfd < 0 &&
+	    (errno == EAFNOSUPPORT || errno == EPERM || errno == EACCES))
+		SKIP(return, "socket(%d, %d, %d) not available: %s",
+		     variant->family, variant->type, variant->protocol,
+		     strerror(errno));
+	ASSERT_GE(self->sockfd, 0) {
+		TH_LOG("Failed to create socket(%d, %d, %d): %s",
+		       variant->family, variant->type, variant->protocol,
+		       strerror(errno));
+	}
+}
+
+FIXTURE_TEARDOWN(xattr_socket_types)
+{
+	if (self->sockfd >= 0)
+		close(self->sockfd);
+}
+
+TEST_F(xattr_socket_types, set_get_list_remove)
+{
+	char buf[256], list[4096], *ptr;
+	ssize_t ret;
+	bool found;
+
+	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));
+	ASSERT_STREQ(buf, TEST_XATTR_VALUE);
+
+	memset(list, 0, sizeof(list));
+	ret = flistxattr(self->sockfd, list, sizeof(list));
+	ASSERT_GT(ret, 0);
+	found = false;
+	for (ptr = list; ptr < list + ret; ptr += strlen(ptr) + 1) {
+		if (strcmp(ptr, TEST_XATTR_NAME) == 0)
+			found = true;
+	}
+	ASSERT_TRUE(found);
+
+	ret = fremovexattr(self->sockfd, TEST_XATTR_NAME);
+	ASSERT_EQ(ret, 0);
+
+	ret = fgetxattr(self->sockfd, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENODATA);
+}
+
+/*
+ * Test abstract namespace AF_UNIX socket.
+ * Abstract sockets don't have a filesystem path; their inodes live in
+ * sockfs so user.* xattrs should work via fsetxattr/fgetxattr.
+ */
+FIXTURE(xattr_abstract)
+{
+	int sockfd;
+};
+
+FIXTURE_SETUP(xattr_abstract)
+{
+	struct sockaddr_un addr;
+	char name[64];
+	int ret, len;
+
+	self->sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
+	ASSERT_GE(self->sockfd, 0);
+
+	len = snprintf(name, sizeof(name), "xattr_test_abstract_%d", getpid());
+
+	memset(&addr, 0, sizeof(addr));
+	addr.sun_family = AF_UNIX;
+	addr.sun_path[0] = '\0';
+	memcpy(&addr.sun_path[1], name, len);
+
+	ret = bind(self->sockfd, (struct sockaddr *)&addr,
+		   offsetof(struct sockaddr_un, sun_path) + 1 + len);
+	ASSERT_EQ(ret, 0);
+}
+
+FIXTURE_TEARDOWN(xattr_abstract)
+{
+	if (self->sockfd >= 0)
+		close(self->sockfd);
+}
+
+TEST_F(xattr_abstract, set_get)
+{
+	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 on abstract socket 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));
+	ASSERT_STREQ(buf, TEST_XATTR_VALUE);
+}
+
+TEST_HARNESS_MAIN