On Sat, Nov 1, 2025 at 10:23 AM Sunday Adelodun adelodunolaoluwa@yahoo.com wrote:

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/af_unix/Makefile | 1 + .../selftests/net/af_unix/unix_connreset.c | 179 ++++++++++++++++++ 2 files changed, 180 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 \
  

patchwork caught this test is not added to .gitignore. https://patchwork.kernel.org/project/netdevbpf/patch/20251101172230.10179-1-...

Could you add it to this file ?

tools/testing/selftests/net/.gitignore

# 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..6f43435d96e2 --- /dev/null +++ b/tools/testing/selftests/net/af_unix/unix_connreset.c @@ -0,0 +1,179 @@ +// 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;
  

+};

+/* Define variants: stream and datagram */

nit: outdated, maybe simply remove ?

+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) {
  

patchwork caught mis-alignment here and other places.

I'm using this for emacs, and other editors will have a similar config.

(setq-default c-default-style "linux")

You can check if lines are aligned properly by

$ git show --format=email | ./scripts/checkpatch.pl

•           err = listen(self->server, 1);
  

•           ASSERT_EQ(0, err);
  

•           self->client = socket(AF_UNIX, variant->socket_type, 0);
  

Could you add SOCK_NONBLOCK here too ?

•           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 ||
  

•           variant->socket_type == SOCK_SEQPACKET)
  

•           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;
  

•   /* Peer closes normally */
  

•   if (variant->socket_type == SOCK_STREAM ||
  

•           variant->socket_type == SOCK_SEQPACKET)
  

•           close(self->child);
  

•   else
  

•           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));
  

errno is undefined if not set, and same for strerror(errno).

Also, if ASSERT_XXX() below fails, the same information (test case, errno) is logged. So, TH_LOG() seems unnecessary.

Maybe try modifying the condition below and see how the assertion is logged.

•   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) +{

•   char buf[16] = {};
  

•   ssize_t n;
  

•   /* 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));
  

•   if (variant->socket_type == SOCK_STREAM ||
  

•           variant->socket_type == SOCK_SEQPACKET) {
  

•           ASSERT_EQ(-1, n);
  

•           ASSERT_EQ(ECONNRESET, errno);
  

•   } else {
  

•           ASSERT_EQ(-1, n);
  

•           ASSERT_EQ(EAGAIN, errno);
  

•   }
  

+}

+/* Test 3: SOCK_DGRAM peer close */

Now Test 2 and Test 3 look identical ;)

Thanks!

+TEST_F(unix_sock, dgram_reset) +{

•   char buf[16] = {};
  

•   ssize_t n;
  

•   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));
  

•   if (variant->socket_type == SOCK_STREAM ||
  

•           variant->socket_type == SOCK_SEQPACKET) {
  

•           ASSERT_EQ(-1, n);
  

•           ASSERT_EQ(ECONNRESET, errno);
  

•   } else {
  

•           ASSERT_EQ(-1, n);
  

•           ASSERT_EQ(EAGAIN, errno);
  

•   }
  

+}

+TEST_HARNESS_MAIN

-- 2.43.0