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@google.com>
Signed-off-by: Sunday Adelodun <adelodunolaoluwa@yahoo.com>
Link: https://patch.msgid.link/20251113112802.44657-1-adelodunolaoluwa@yahoo.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

authored by

Sunday Adelodun and committed by

Paolo Abeni 7 months ago 45a1cd83 4e1b0afa

+179

3 changed files

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tools

testing

selftests

net

.gitignore

af_unix

Makefile

unix_connreset.c

tools/testing/selftests/net/.gitignore

··· 65 65 udpgso_bench_rx 66 66 udpgso_bench_tx 67 67 unix_connect 68 + unix_connreset

tools/testing/selftests/net/af_unix/Makefile

··· 7 7 scm_pidfd \ 8 8 scm_rights \ 9 9 unix_connect \ 10 + unix_connreset \ 10 11 # end of TEST_GEN_PROGS 11 12 12 13 include ../../lib.mk

+177

tools/testing/selftests/net/af_unix/unix_connreset.c

··· 1 + // SPDX-License-Identifier: GPL-2.0 2 + /* 3 + * Selftest for AF_UNIX socket close and ECONNRESET behaviour. 4 + * 5 + * This test verifies: 6 + * 1. SOCK_STREAM returns EOF when the peer closes normally. 7 + * 2. SOCK_STREAM returns ECONNRESET if peer closes with unread data. 8 + * 3. SOCK_SEQPACKET returns EOF when the peer closes normally. 9 + * 4. SOCK_SEQPACKET returns ECONNRESET if the peer closes with unread data. 10 + * 5. SOCK_DGRAM does not return ECONNRESET when the peer closes. 11 + * 12 + * These tests document the intended Linux behaviour. 13 + * 14 + */ 15 + 16 + #define _GNU_SOURCE 17 + #include <stdlib.h> 18 + #include <string.h> 19 + #include <fcntl.h> 20 + #include <unistd.h> 21 + #include <errno.h> 22 + #include <sys/socket.h> 23 + #include <sys/un.h> 24 + #include "../../kselftest_harness.h" 25 + 26 + #define SOCK_PATH "/tmp/af_unix_connreset.sock" 27 + 28 + static void remove_socket_file(void) 29 + { 30 + unlink(SOCK_PATH); 31 + } 32 + 33 + FIXTURE(unix_sock) 34 + { 35 + int server; 36 + int client; 37 + int child; 38 + }; 39 + 40 + FIXTURE_VARIANT(unix_sock) 41 + { 42 + int socket_type; 43 + const char *name; 44 + }; 45 + 46 + FIXTURE_VARIANT_ADD(unix_sock, stream) { 47 + .socket_type = SOCK_STREAM, 48 + .name = "SOCK_STREAM", 49 + }; 50 + 51 + FIXTURE_VARIANT_ADD(unix_sock, dgram) { 52 + .socket_type = SOCK_DGRAM, 53 + .name = "SOCK_DGRAM", 54 + }; 55 + 56 + FIXTURE_VARIANT_ADD(unix_sock, seqpacket) { 57 + .socket_type = SOCK_SEQPACKET, 58 + .name = "SOCK_SEQPACKET", 59 + }; 60 + 61 + FIXTURE_SETUP(unix_sock) 62 + { 63 + struct sockaddr_un addr = {}; 64 + int err; 65 + 66 + addr.sun_family = AF_UNIX; 67 + strcpy(addr.sun_path, SOCK_PATH); 68 + remove_socket_file(); 69 + 70 + self->server = socket(AF_UNIX, variant->socket_type, 0); 71 + ASSERT_LT(-1, self->server); 72 + 73 + err = bind(self->server, (struct sockaddr *)&addr, sizeof(addr)); 74 + ASSERT_EQ(0, err); 75 + 76 + if (variant->socket_type == SOCK_STREAM || 77 + variant->socket_type == SOCK_SEQPACKET) { 78 + err = listen(self->server, 1); 79 + ASSERT_EQ(0, err); 80 + } 81 + 82 + self->client = socket(AF_UNIX, variant->socket_type | SOCK_NONBLOCK, 0); 83 + ASSERT_LT(-1, self->client); 84 + 85 + err = connect(self->client, (struct sockaddr *)&addr, sizeof(addr)); 86 + ASSERT_EQ(0, err); 87 + } 88 + 89 + FIXTURE_TEARDOWN(unix_sock) 90 + { 91 + if (variant->socket_type == SOCK_STREAM || 92 + variant->socket_type == SOCK_SEQPACKET) 93 + close(self->child); 94 + 95 + close(self->client); 96 + close(self->server); 97 + remove_socket_file(); 98 + } 99 + 100 + /* Test 1: peer closes normally */ 101 + TEST_F(unix_sock, eof) 102 + { 103 + char buf[16] = {}; 104 + ssize_t n; 105 + 106 + if (variant->socket_type == SOCK_STREAM || 107 + variant->socket_type == SOCK_SEQPACKET) { 108 + self->child = accept(self->server, NULL, NULL); 109 + ASSERT_LT(-1, self->child); 110 + 111 + close(self->child); 112 + } else { 113 + close(self->server); 114 + } 115 + 116 + n = recv(self->client, buf, sizeof(buf), 0); 117 + 118 + if (variant->socket_type == SOCK_STREAM || 119 + variant->socket_type == SOCK_SEQPACKET) { 120 + ASSERT_EQ(0, n); 121 + } else { 122 + ASSERT_EQ(-1, n); 123 + ASSERT_EQ(EAGAIN, errno); 124 + } 125 + } 126 + 127 + /* Test 2: peer closes with unread data */ 128 + TEST_F(unix_sock, reset_unread_behavior) 129 + { 130 + char buf[16] = {}; 131 + ssize_t n; 132 + 133 + /* Send data that will remain unread */ 134 + send(self->client, "hello", 5, 0); 135 + 136 + if (variant->socket_type == SOCK_DGRAM) { 137 + /* No real connection, just close the server */ 138 + close(self->server); 139 + } else { 140 + self->child = accept(self->server, NULL, NULL); 141 + ASSERT_LT(-1, self->child); 142 + 143 + /* Peer closes before client reads */ 144 + close(self->child); 145 + } 146 + 147 + n = recv(self->client, buf, sizeof(buf), 0); 148 + ASSERT_EQ(-1, n); 149 + 150 + if (variant->socket_type == SOCK_STREAM || 151 + variant->socket_type == SOCK_SEQPACKET) { 152 + ASSERT_EQ(ECONNRESET, errno); 153 + } else { 154 + ASSERT_EQ(EAGAIN, errno); 155 + } 156 + } 157 + 158 + /* Test 3: closing unaccepted (embryo) server socket should reset client. */ 159 + TEST_F(unix_sock, reset_closed_embryo) 160 + { 161 + char buf[16] = {}; 162 + ssize_t n; 163 + 164 + if (variant->socket_type == SOCK_DGRAM) 165 + SKIP(return, "This test only applies to SOCK_STREAM and SOCK_SEQPACKET"); 166 + 167 + /* Close server without accept()ing */ 168 + close(self->server); 169 + 170 + n = recv(self->client, buf, sizeof(buf), 0); 171 + 172 + ASSERT_EQ(-1, n); 173 + ASSERT_EQ(ECONNRESET, errno); 174 + } 175 + 176 + TEST_HARNESS_MAIN 177 +

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