[PATCH v2] selftests: af_unix: Add tests for ECONNRESET and EOF semantics - Linux-kselftest-mirror

25 Oct 2025

Add selftests to verify and document Linux’s intended behaviour for
UNIX domain sockets (SOCK_STREAM and SOCK_DGRAM) when a peer closes.
The tests cover:
1. EOF returned when a SOCK_STREAM peer closes normally.
  2. ECONNRESET returned when a SOCK_STREAM peer closes with unread data.
  3. SOCK_DGRAM sockets not returning ECONNRESET on peer close.
This follows up on review feedback suggesting a selftest to clarify
Linux’s semantics.
Suggested-by: Kuniyuki Iwashima kuniyu@google.com
Signed-off-by: Sunday Adelodun adelodunolaoluwa@yahoo.com
---
Changelog:
Changes made from v1:
- Patch prefix updated to selftest: af_unix:.
- All mentions of “UNIX” changed to AF_UNIX.
- Removed BSD references from comments.
- Shared setup refactored using FIXTURE_VARIANT().
- Cleanup moved to FIXTURE_TEARDOWN() to always run.
- Tests consolidated to reduce duplication: EOF, ECONNRESET, SOCK_DGRAM peer close.
- Corrected ASSERT usage and initialization style.
- Makefile updated for new directory af_unix.
tools/testing/selftests/net/af_unix/Makefile  |   1 +
 .../selftests/net/af_unix/unix_connreset.c    | 161 ++++++++++++++++++
 2 files changed, 162 insertions(+)
 create mode 100644 tools/testing/selftests/net/af_unix/unix_connreset.c

diff --git a/tools/testing/selftests/net/af_unix/Makefile b/tools/testing/selftests/net/af_unix/Makefile
index de805cbbdf69..5826a8372451 100644
--- a/tools/testing/selftests/net/af_unix/Makefile
+++ b/tools/testing/selftests/net/af_unix/Makefile
@@ -7,6 +7,7 @@ TEST_GEN_PROGS := \
    scm_pidfd \
    scm_rights \
    unix_connect \
+	unix_connreset \
 # end of TEST_GEN_PROGS
include ../../lib.mk
diff --git a/tools/testing/selftests/net/af_unix/unix_connreset.c b/tools/testing/selftests/net/af_unix/unix_connreset.c
new file mode 100644
index 000000000000..c65ec997d77d
--- /dev/null
+++ b/tools/testing/selftests/net/af_unix/unix_connreset.c
@@ -0,0 +1,161 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Selftest for AF_UNIX socket close and ECONNRESET behaviour.
+ *
+ * This test verifies that:
+ *  1. SOCK_STREAM sockets return EOF when peer closes normally.
+ *  2. SOCK_STREAM sockets return ECONNRESET if peer closes with unread data.
+ *  3. SOCK_DGRAM sockets do not return ECONNRESET when peer closes.
+ *
+ * These tests document the intended Linux behaviour.
+ *
+ */
+
+#define _GNU_SOURCE
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include "../../kselftest_harness.h"
+
+#define SOCK_PATH "/tmp/af_unix_connreset.sock"
+
+static void remove_socket_file(void)
+{
+	unlink(SOCK_PATH);
+}
+
+FIXTURE(unix_sock)
+{
+	int server;
+	int client;
+	int child;
+};
+
+FIXTURE_VARIANT(unix_sock)
+{
+	int socket_type;
+	const char *name;
+};
+
+/* Define variants: stream and datagram */
+FIXTURE_VARIANT_ADD(unix_sock, stream) {
+	.socket_type = SOCK_STREAM,
+	.name = "SOCK_STREAM",
+};
+
+FIXTURE_VARIANT_ADD(unix_sock, dgram) {
+	.socket_type = SOCK_DGRAM,
+	.name = "SOCK_DGRAM",
+};
+
+FIXTURE_SETUP(unix_sock)
+{
+	struct sockaddr_un addr = {};
+	int err;
+
+	addr.sun_family = AF_UNIX;
+	strcpy(addr.sun_path, SOCK_PATH);
+
+	self->server = socket(AF_UNIX, variant->socket_type, 0);
+	ASSERT_LT(-1, self->server);
+
+	err = bind(self->server, (struct sockaddr *)&addr, sizeof(addr));
+	ASSERT_EQ(0, err);
+
+	if (variant->socket_type == SOCK_STREAM) {
+		err = listen(self->server, 1);
+		ASSERT_EQ(0, err);
+
+		self->client = socket(AF_UNIX, SOCK_STREAM, 0);
+		ASSERT_LT(-1, self->client);
+
+		err = connect(self->client, (struct sockaddr *)&addr, sizeof(addr));
+		ASSERT_EQ(0, err);
+
+		self->child = accept(self->server, NULL, NULL);
+		ASSERT_LT(-1, self->child);
+	} else {
+		/* Datagram: bind and connect only */
+		self->client = socket(AF_UNIX, SOCK_DGRAM | SOCK_NONBLOCK, 0);
+		ASSERT_LT(-1, self->client);
+
+		err = connect(self->client, (struct sockaddr *)&addr, sizeof(addr));
+		ASSERT_EQ(0, err);
+	}
+}
+
+FIXTURE_TEARDOWN(unix_sock)
+{
+	if (variant->socket_type == SOCK_STREAM)
+		close(self->child);
+
+	close(self->client);
+	close(self->server);
+	remove_socket_file();
+}
+
+/* Test 1: peer closes normally */
+TEST_F(unix_sock, eof)
+{
+	char buf[16] = {};
+	ssize_t n;
+
+	if (variant->socket_type != SOCK_STREAM)
+		SKIP(return, "This test only applies to SOCK_STREAM");
+
+	/* Peer closes normally */
+	close(self->child);
+
+	n = recv(self->client, buf, sizeof(buf), 0);
+	TH_LOG("%s: recv=%zd errno=%d (%s)", variant->name, n, errno, strerror(errno));
+	if (n == -1)
+		ASSERT_EQ(ECONNRESET, errno);
+
+	if (n != -1)
+		ASSERT_EQ(0, n);
+}
+
+/* Test 2: peer closes with unread data */
+TEST_F(unix_sock, reset_unread)
+{
+	char buf[16] = {};
+	ssize_t n;
+
+	if (variant->socket_type != SOCK_STREAM)
+		SKIP(return, "This test only applies to SOCK_STREAM");
+
+	/* Send data that will remain unread by client */
+	send(self->client, "hello", 5, 0);
+	close(self->child);
+
+	n = recv(self->client, buf, sizeof(buf), 0);
+	TH_LOG("%s: recv=%zd errno=%d (%s)", variant->name, n, errno, strerror(errno));
+	ASSERT_EQ(-1, n);
+	ASSERT_EQ(ECONNRESET, errno);
+}
+
+/* Test 3: SOCK_DGRAM peer close */
+TEST_F(unix_sock, dgram_reset)
+{
+	char buf[16] = {};
+	ssize_t n;
+
+	if (variant->socket_type != SOCK_DGRAM)
+		SKIP(return, "This test only applies to SOCK_DGRAM");
+
+	send(self->client, "hello", 5, 0);
+	close(self->server);
+
+	n = recv(self->client, buf, sizeof(buf), 0);
+	TH_LOG("%s: recv=%zd errno=%d (%s)", variant->name, n, errno, strerror(errno));
+	/* Expect EAGAIN because there is no datagram and peer is closed. */
+	ASSERT_EQ(-1, n);
+	ASSERT_EQ(EAGAIN, errno);
+}
+
+TEST_HARNESS_MAIN
+
-- 
2.43.0



    