[PATCH v4] selftests: af_unix: Add tests for ECONNRESET and EOF semantics

Sunday Adelodun
2025-11-12T21:30:49Z

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 verify that:

1. SOCK_STREAM returns EOF when the peer closes normally.
2. SOCK_STREAM returns ECONNRESET if the peer closes with unread data.
3. SOCK_SEQPACKET returns EOF when the peer closes normally.
4. SOCK_SEQPACKET returns ECONNRESET if the peer closes with unread data.
5. SOCK_DGRAM does not return ECONNRESET when the peer closes.

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>
---
tools/testing/selftests/net/.gitignore | 1 +
tools/testing/selftests/net/af_unix/Makefile | 1 +
.../selftests/net/af_unix/unix_connreset.c | 178 ++++++++++++++++++
3 files changed, 180 insertions(+)
create mode 100644 tools/testing/selftests/net/af_unix/unix_connreset.c

diff --git a/tools/testing/selftests/net/.gitignore b/tools/testing/selftests/net/.gitignore
index 439101b518ee..e89a60581a13 100644
--- a/tools/testing/selftests/net/.gitignore
+++ b/tools/testing/selftests/net/.gitignore
@@ -65,3 +65,4 @@ udpgso
udpgso_bench_rx
udpgso_bench_tx
unix_connect
+unix_connreset
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..9413f8a0814f
--- /dev/null
+++ b/tools/testing/selftests/net/af_unix/unix_connreset.c
@@ -0,0 +1,178 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Selftest for AF_UNIX socket close and ECONNRESET behaviour.
+ *
+ * This test verifies:
+ * 1. SOCK_STREAM returns EOF when the peer closes normally.
+ * 2. SOCK_STREAM returns ECONNRESET if peer closes with unread data.
+ * 3. SOCK_SEQPACKET returns EOF when the peer closes normally.
+ * 4. SOCK_SEQPACKET returns ECONNRESET if the peer closes with unread data.
+ * 5. SOCK_DGRAM does not return ECONNRESET when the 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;
+};
+
+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_VARIANT_ADD(unix_sock, seqpacket) {
+ .socket_type = SOCK_SEQPACKET,
+ .name = "SOCK_SEQPACKET",
+};
+
+FIXTURE_SETUP(unix_sock)
+{
+ struct sockaddr_un addr = {};
+ int err;
+
+ addr.sun_family = AF_UNIX;
+ strcpy(addr.sun_path, SOCK_PATH);
+ remove_socket_file();
+
+ 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 ||
+ variant->socket_type == SOCK_SEQPACKET) {
+ err = listen(self->server, 1);
+ ASSERT_EQ(0, err);
+ }
+
+ self->client = socket(AF_UNIX, variant->socket_type | 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 ||
+ variant->socket_type == SOCK_SEQPACKET) & self->child > 0)
+ 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 ||
+ variant->socket_type == SOCK_SEQPACKET) {
+ self->child = accept(self->server, NULL, NULL);
+ ASSERT_LT(-1, self->child);
+
+ close(self->child);
+ } else {
+ close(self->server);
+ }
+
+ n = recv(self->client, buf, sizeof(buf), 0);
+
+ if (variant->socket_type == SOCK_STREAM ||
+ variant->socket_type == SOCK_SEQPACKET) {
+ ASSERT_EQ(0, n);
+ } else {
+ ASSERT_EQ(-1, n);
+ ASSERT_EQ(EAGAIN, errno);
+ }
+}
+
+/* Test 2: peer closes with unread data */
+TEST_F(unix_sock, reset_unread_behavior)
+{
+ char buf[16] = {};
+ ssize_t n;
+
+ if (variant->socket_type == SOCK_DGRAM) {
+ /* No real connection, just close the server */
+ close(self->server);
+ } else {
+ /* Establish full connection first */
+ self->child = accept(self->server, NULL, NULL);
+ ASSERT_LT(-1, self->child);
+
+ /* Send data that will remain unread */
+ send(self->client, "hello", 5, 0);
+
+ /* Peer closes before client reads */
+ close(self->child);
+ }
+
+ n = recv(self->client, buf, sizeof(buf), 0);
+ ASSERT_EQ(-1, n);
+
+ if (variant->socket_type == SOCK_STREAM ||
+ variant->socket_type == SOCK_SEQPACKET) {
+ ASSERT_EQ(ECONNRESET, errno);
+ } else {
+ ASSERT_EQ(EAGAIN, errno);
+ }
+}
+
+/* Test 3: closing unaccepted (embryo) server socket should reset client. */
+TEST_F(unix_sock, reset_closed_embryo)
+{
+ char buf[16] = {};
+ ssize_t n;
+
+ if (variant->socket_type == SOCK_DGRAM)
+ SKIP(return, "This test only applies to SOCK_STREAM and SOCK_SEQPACKET");
+
+ /* Close server without accept()ing */
+ close(self->server);
+
+ n = recv(self->client, buf, sizeof(buf), 0);
+
+ ASSERT_EQ(-1, n);
+ ASSERT_EQ(ECONNRESET, errno);
+}
+
+TEST_HARNESS_MAIN
+
--
2.43.0