[PATCH 12/14] selftests/xattr: path-based AF_UNIX socket xattr tests

[Christian Brauner]

Test user.* extended attribute operations on path-based Unix domain
sockets (SOCK_STREAM, SOCK_DGRAM, SOCK_SEQPACKET). Path-based sockets
are bound to a filesystem path and their inodes live on the underlying
filesystem (e.g. tmpfs).

Covers set/get/list/remove, persistence, XATTR_CREATE/XATTR_REPLACE
flags, empty values, size queries, buffer-too-small errors, O_PATH fd
operations, and trusted.* xattr handling.

Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
 .../testing/selftests/filesystems/xattr/.gitignore |   1 +
 tools/testing/selftests/filesystems/xattr/Makefile |   6 +
 .../filesystems/xattr/xattr_socket_test.c          | 470 +++++++++++++++++++++
 3 files changed, 477 insertions(+)

diff --git a/tools/testing/selftests/filesystems/xattr/.gitignore b/tools/testing/selftests/filesystems/xattr/.gitignore
new file mode 100644
index 000000000000..5fd015d2257a
--- /dev/null
+++ b/tools/testing/selftests/filesystems/xattr/.gitignore
@@ -0,0 +1 @@
+xattr_socket_test
diff --git a/tools/testing/selftests/filesystems/xattr/Makefile b/tools/testing/selftests/filesystems/xattr/Makefile
new file mode 100644
index 000000000000..e3d8dca80faa
--- /dev/null
+++ b/tools/testing/selftests/filesystems/xattr/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CFLAGS += $(KHDR_INCLUDES)
+TEST_GEN_PROGS := xattr_socket_test
+
+include ../../lib.mk
diff --git a/tools/testing/selftests/filesystems/xattr/xattr_socket_test.c b/tools/testing/selftests/filesystems/xattr/xattr_socket_test.c
new file mode 100644
index 000000000000..fac0a4c6bc05
--- /dev/null
+++ b/tools/testing/selftests/filesystems/xattr/xattr_socket_test.c
@@ -0,0 +1,470 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2026 Christian Brauner <brauner@xxxxxxxxxx>
+/*
+ * Test extended attributes on path-based Unix domain sockets.
+ *
+ * Path-based Unix domain sockets are bound to a filesystem path and their
+ * inodes live on the underlying filesystem (e.g. tmpfs). These tests verify
+ * that user.* and trusted.* xattr operations work correctly on them using
+ * path-based syscalls (setxattr, getxattr, etc.).
+ *
+ * Covers SOCK_STREAM, SOCK_DGRAM, and SOCK_SEQPACKET socket types.
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/un.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"
+
+/*
+ * Fixture for path-based Unix domain socket tests.
+ * Creates a SOCK_STREAM socket bound to a path in /tmp (typically tmpfs).
+ */
+FIXTURE(xattr_socket)
+{
+	char socket_path[PATH_MAX];
+	int sockfd;
+};
+
+FIXTURE_VARIANT(xattr_socket)
+{
+	int sock_type;
+	const char *name;
+};
+
+FIXTURE_VARIANT_ADD(xattr_socket, stream) {
+	.sock_type = SOCK_STREAM,
+	.name = "stream",
+};
+
+FIXTURE_VARIANT_ADD(xattr_socket, dgram) {
+	.sock_type = SOCK_DGRAM,
+	.name = "dgram",
+};
+
+FIXTURE_VARIANT_ADD(xattr_socket, seqpacket) {
+	.sock_type = SOCK_SEQPACKET,
+	.name = "seqpacket",
+};
+
+FIXTURE_SETUP(xattr_socket)
+{
+	struct sockaddr_un addr;
+	int ret;
+
+	self->sockfd = -1;
+
+	snprintf(self->socket_path, sizeof(self->socket_path),
+		 "/tmp/xattr_socket_test_%s.%d", variant->name, getpid());
+	unlink(self->socket_path);
+
+	self->sockfd = socket(AF_UNIX, variant->sock_type, 0);
+	ASSERT_GE(self->sockfd, 0) {
+		TH_LOG("Failed to create socket: %s", strerror(errno));
+	}
+
+	memset(&addr, 0, sizeof(addr));
+	addr.sun_family = AF_UNIX;
+	strncpy(addr.sun_path, self->socket_path, sizeof(addr.sun_path) - 1);
+
+	ret = bind(self->sockfd, (struct sockaddr *)&addr, sizeof(addr));
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("Failed to bind socket to %s: %s",
+		       self->socket_path, strerror(errno));
+	}
+}
+
+FIXTURE_TEARDOWN(xattr_socket)
+{
+	if (self->sockfd >= 0)
+		close(self->sockfd);
+	unlink(self->socket_path);
+}
+
+TEST_F(xattr_socket, set_user_xattr)
+{
+	int ret;
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("setxattr failed: %s (errno=%d)", strerror(errno), errno);
+	}
+}
+
+TEST_F(xattr_socket, get_user_xattr)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("setxattr failed: %s", strerror(errno));
+	}
+
+	memset(buf, 0, sizeof(buf));
+	ret = getxattr(self->socket_path, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, (ssize_t)strlen(TEST_XATTR_VALUE)) {
+		TH_LOG("getxattr returned %zd, expected %zu: %s",
+		       ret, strlen(TEST_XATTR_VALUE), strerror(errno));
+	}
+	ASSERT_STREQ(buf, TEST_XATTR_VALUE);
+}
+
+TEST_F(xattr_socket, list_user_xattr)
+{
+	char list[1024];
+	ssize_t ret;
+	bool found = false;
+	char *ptr;
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("setxattr failed: %s", strerror(errno));
+	}
+
+	memset(list, 0, sizeof(list));
+	ret = listxattr(self->socket_path, list, sizeof(list));
+	ASSERT_GT(ret, 0) {
+		TH_LOG("listxattr failed: %s", strerror(errno));
+	}
+
+	for (ptr = list; ptr < list + ret; ptr += strlen(ptr) + 1) {
+		if (strcmp(ptr, TEST_XATTR_NAME) == 0) {
+			found = true;
+			break;
+		}
+	}
+	ASSERT_TRUE(found) {
+		TH_LOG("xattr %s not found in list", TEST_XATTR_NAME);
+	}
+}
+
+TEST_F(xattr_socket, remove_user_xattr)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("setxattr failed: %s", strerror(errno));
+	}
+
+	ret = removexattr(self->socket_path, TEST_XATTR_NAME);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("removexattr failed: %s", strerror(errno));
+	}
+
+	ret = getxattr(self->socket_path, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENODATA) {
+		TH_LOG("Expected ENODATA, got %s", strerror(errno));
+	}
+}
+
+/*
+ * Test that xattrs persist across socket close and reopen.
+ * The xattr is on the filesystem inode, not the socket fd.
+ */
+TEST_F(xattr_socket, xattr_persistence)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("setxattr failed: %s", strerror(errno));
+	}
+
+	close(self->sockfd);
+	self->sockfd = -1;
+
+	memset(buf, 0, sizeof(buf));
+	ret = getxattr(self->socket_path, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, (ssize_t)strlen(TEST_XATTR_VALUE)) {
+		TH_LOG("getxattr after close failed: %s", strerror(errno));
+	}
+	ASSERT_STREQ(buf, TEST_XATTR_VALUE);
+}
+
+TEST_F(xattr_socket, update_user_xattr)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE2, strlen(TEST_XATTR_VALUE2), 0);
+	ASSERT_EQ(ret, 0);
+
+	memset(buf, 0, sizeof(buf));
+	ret = getxattr(self->socket_path, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, (ssize_t)strlen(TEST_XATTR_VALUE2));
+	ASSERT_STREQ(buf, TEST_XATTR_VALUE2);
+}
+
+TEST_F(xattr_socket, xattr_create_flag)
+{
+	int ret;
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE2, strlen(TEST_XATTR_VALUE2), XATTR_CREATE);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, EEXIST);
+}
+
+TEST_F(xattr_socket, xattr_replace_flag)
+{
+	int ret;
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), XATTR_REPLACE);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENODATA);
+}
+
+TEST_F(xattr_socket, multiple_xattrs)
+{
+	char buf[256];
+	ssize_t ret;
+	int i;
+	char name[64], value[64];
+	const int num_xattrs = 5;
+
+	for (i = 0; i < num_xattrs; i++) {
+		snprintf(name, sizeof(name), "user.test%d", i);
+		snprintf(value, sizeof(value), "value%d", i);
+		ret = setxattr(self->socket_path, name, value, strlen(value), 0);
+		ASSERT_EQ(ret, 0) {
+			TH_LOG("setxattr %s failed: %s", name, strerror(errno));
+		}
+	}
+
+	for (i = 0; i < num_xattrs; i++) {
+		snprintf(name, sizeof(name), "user.test%d", i);
+		snprintf(value, sizeof(value), "value%d", i);
+		memset(buf, 0, sizeof(buf));
+		ret = getxattr(self->socket_path, name, buf, sizeof(buf));
+		ASSERT_EQ(ret, (ssize_t)strlen(value));
+		ASSERT_STREQ(buf, value);
+	}
+}
+
+TEST_F(xattr_socket, xattr_empty_value)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME, "", 0, 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = getxattr(self->socket_path, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, 0);
+}
+
+TEST_F(xattr_socket, xattr_get_size)
+{
+	ssize_t ret;
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = getxattr(self->socket_path, TEST_XATTR_NAME, NULL, 0);
+	ASSERT_EQ(ret, (ssize_t)strlen(TEST_XATTR_VALUE));
+}
+
+TEST_F(xattr_socket, xattr_buffer_too_small)
+{
+	char buf[2];
+	ssize_t ret;
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = getxattr(self->socket_path, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ERANGE);
+}
+
+TEST_F(xattr_socket, xattr_nonexistent)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = getxattr(self->socket_path, "user.nonexistent", buf, sizeof(buf));
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENODATA);
+}
+
+TEST_F(xattr_socket, remove_nonexistent_xattr)
+{
+	int ret;
+
+	ret = removexattr(self->socket_path, "user.nonexistent");
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENODATA);
+}
+
+TEST_F(xattr_socket, large_xattr_value)
+{
+	char large_value[4096];
+	char read_buf[4096];
+	ssize_t ret;
+
+	memset(large_value, 'A', sizeof(large_value));
+
+	ret = setxattr(self->socket_path, TEST_XATTR_NAME,
+		       large_value, sizeof(large_value), 0);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("setxattr with large value failed: %s", strerror(errno));
+	}
+
+	memset(read_buf, 0, sizeof(read_buf));
+	ret = getxattr(self->socket_path, TEST_XATTR_NAME,
+		       read_buf, sizeof(read_buf));
+	ASSERT_EQ(ret, (ssize_t)sizeof(large_value));
+	ASSERT_EQ(memcmp(large_value, read_buf, sizeof(large_value)), 0);
+}
+
+/*
+ * Test lsetxattr/lgetxattr (don't follow symlinks).
+ * Socket files aren't symlinks, so this should work the same.
+ */
+TEST_F(xattr_socket, lsetxattr_lgetxattr)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = lsetxattr(self->socket_path, TEST_XATTR_NAME,
+			TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("lsetxattr failed: %s", strerror(errno));
+	}
+
+	memset(buf, 0, sizeof(buf));
+	ret = lgetxattr(self->socket_path, TEST_XATTR_NAME, buf, sizeof(buf));
+	ASSERT_EQ(ret, (ssize_t)strlen(TEST_XATTR_VALUE));
+	ASSERT_STREQ(buf, TEST_XATTR_VALUE);
+}
+
+/*
+ * Fixture for trusted.* xattr tests.
+ * These require CAP_SYS_ADMIN.
+ */
+FIXTURE(xattr_socket_trusted)
+{
+	char socket_path[PATH_MAX];
+	int sockfd;
+};
+
+FIXTURE_VARIANT(xattr_socket_trusted)
+{
+	int sock_type;
+	const char *name;
+};
+
+FIXTURE_VARIANT_ADD(xattr_socket_trusted, stream) {
+	.sock_type = SOCK_STREAM,
+	.name = "stream",
+};
+
+FIXTURE_VARIANT_ADD(xattr_socket_trusted, dgram) {
+	.sock_type = SOCK_DGRAM,
+	.name = "dgram",
+};
+
+FIXTURE_VARIANT_ADD(xattr_socket_trusted, seqpacket) {
+	.sock_type = SOCK_SEQPACKET,
+	.name = "seqpacket",
+};
+
+FIXTURE_SETUP(xattr_socket_trusted)
+{
+	struct sockaddr_un addr;
+	int ret;
+
+	self->sockfd = -1;
+
+	snprintf(self->socket_path, sizeof(self->socket_path),
+		 "/tmp/xattr_socket_trusted_%s.%d", variant->name, getpid());
+	unlink(self->socket_path);
+
+	self->sockfd = socket(AF_UNIX, variant->sock_type, 0);
+	ASSERT_GE(self->sockfd, 0);
+
+	memset(&addr, 0, sizeof(addr));
+	addr.sun_family = AF_UNIX;
+	strncpy(addr.sun_path, self->socket_path, sizeof(addr.sun_path) - 1);
+
+	ret = bind(self->sockfd, (struct sockaddr *)&addr, sizeof(addr));
+	ASSERT_EQ(ret, 0);
+}
+
+FIXTURE_TEARDOWN(xattr_socket_trusted)
+{
+	if (self->sockfd >= 0)
+		close(self->sockfd);
+	unlink(self->socket_path);
+}
+
+TEST_F(xattr_socket_trusted, set_trusted_xattr)
+{
+	char buf[256];
+	ssize_t len;
+	int ret;
+
+	ret = setxattr(self->socket_path, "trusted.testattr",
+		       TEST_XATTR_VALUE, strlen(TEST_XATTR_VALUE), 0);
+	if (ret == -1 && errno == EPERM)
+		SKIP(return, "Need CAP_SYS_ADMIN for trusted.* xattrs");
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("setxattr trusted.testattr failed: %s", strerror(errno));
+	}
+
+	memset(buf, 0, sizeof(buf));
+	len = getxattr(self->socket_path, "trusted.testattr",
+		       buf, sizeof(buf));
+	ASSERT_EQ(len, (ssize_t)strlen(TEST_XATTR_VALUE));
+	ASSERT_STREQ(buf, TEST_XATTR_VALUE);
+}
+
+TEST_F(xattr_socket_trusted, get_trusted_xattr_unprivileged)
+{
+	char buf[256];
+	ssize_t ret;
+
+	ret = getxattr(self->socket_path, "trusted.testattr", buf, sizeof(buf));
+	ASSERT_EQ(ret, -1);
+	ASSERT_TRUE(errno == ENODATA || errno == EPERM) {
+		TH_LOG("Expected ENODATA or EPERM, got %s", strerror(errno));
+	}
+}
+
+TEST_HARNESS_MAIN

-- 
2.47.3