Re: [PATCH v3] selftests: af_unix: Add tests for ECONNRESET and EOF semantics

Kuniyuki Iwashima
2025-11-02T07:32:46Z

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-adelodunolaoluwa@yahoo.com/

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
>