Message-ID: <20251113071756.40118-1-adelodunolaoluwa@yahoo.com>
Date: Thu, 13 Nov 2025 08:17:56 +0100
From: Sunday Adelodun <adelodunolaoluwa@...oo.com>
To: kuniyu@...gle.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	horms@...nel.org,
	shuah@...nel.org
Cc: skhan@...uxfoundation.org,
	david.hunter.linux@...il.com,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	linux-kernel-mentees@...ts.linuxfoundation.org,
	Sunday Adelodun <adelodunolaoluwa@...oo.com>
Subject: [PATCH v5] selftests: af_unix: Add tests for ECONNRESET and EOF semantics

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@...gle.com>
Signed-off-by: Sunday Adelodun <adelodunolaoluwa@...oo.com>
---
Changelog:

changes made in v4 to v5:
1. Moved the send() call before the socket type check in Test 2 to ensure
   the unread data behavior is tested for SOCK_DGRAM as well.

2. Removed the misleading commend about accept() for clarity.

3. Applied indentation fixes for style consistency
   (alignment with open parenthesis).

4. Minor comment and formatting cleanups for clarity and adherence
   to kernel coding style.

 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..9cb0f48597eb
--- /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;
+
+	/* Send data that will remain unread */
+	send(self->client, "hello", 5, 0);
+
+	if (variant->socket_type == SOCK_DGRAM) {
+		/* No real connection, just close the server */
+		close(self->server);
+	} else {
+		/* Accept client connection */
+		self->child = accept(self->server, NULL, NULL);
+		ASSERT_LT(-1, self->child);
+
+		/* 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

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