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Message-ID: <CAAVpQUAbDfaiAZ_NCppGE5vsafWoU7V1xvnqtQQM44cwv6jHsA@mail.gmail.com>
Date: Tue, 28 Oct 2025 11:28:14 -0700
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Sunday Adelodun <adelodunolaoluwa@...oo.com>
Cc: "=David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
Shuah Khan <shuah@...nel.org>, Shuah Khan <skhan@...uxfoundation.org>,
David Hunter <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
Subject: Re: [PATCH v2] selftests: af_unix: Add tests for ECONNRESET and EOF semantics
On Sat, Oct 25, 2025 at 12:03 PM Sunday Adelodun
<adelodunolaoluwa@...oo.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 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@...gle.com>
> Signed-off-by: Sunday Adelodun <adelodunolaoluwa@...oo.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",
> +};
Let's add coverage for SOCK_SEQPACKET,
which needs listen() / connect() but other semantics
are similar to 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");
Instead of skipping, let's define final ASSERT() results
for each type.
Same for other 2 tests.
> +
> + /* 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);
... otherwise, we don't see an error here
> +
> + if (n != -1)
> + ASSERT_EQ(0, n);
and this can be checked unconditionally.
> +}
> +
> +/* 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
>
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