Re: [PATCH v3] selftests: af_unix: Add tests for ECONNRESET and EOF semantics
From: Kuniyuki Iwashima <kuniyu@google.com>
Date: 2025-11-02 07:32:45
Also in:
linux-kernel-mentees, linux-kselftest, lkml
On Sat, Nov 1, 2025 at 10:23 AM Sunday Adelodun [off-list ref] wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- 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.cdiff --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
quoted hunk ↗ jump to hunk
# end of TEST_GEN_PROGS include ../../lib.mkdiff --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