Re: [PATCH net v2 2/3] selftests/net/af_unix: test listen() rejects wrong socket states

[Kuniyuki Iwashima]

On Fri, Jul 3, 2026 at 1:15 AM John Ericson
<John.Ericson@obsidian.systems> wrote:
>
> From: John Ericson <mail@xxxxxxxxxxxxxx>
>
> Add a regression test for the `unix_listen()` state check. The key case
> is `listen()` on a bound socket that has already been connected: it is
> no longer in `TCP_CLOSE` or `TCP_LISTEN`, so it must fail with `EINVAL`.
> A `prepare_peercred()` call slipped in ahead of that check once left
> `err` at 0 and made `listen()` silently succeed there instead; this
> guards against a repeat.
>
> The neighbouring outcomes are covered too so they cannot regress the
> same way: a bound socket in `TCP_CLOSE` listens fine, re-`listen()`ing a
> socket already in `TCP_LISTEN` is allowed, and an unbound socket fails
> with `EINVAL`.
>
> Fixes: fd0a109a0f6b ("net, pidfs: prepare for handing out pidfds for reaped sk->sk_peer_pid")
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: John Ericson <mail@xxxxxxxxxxxxxx>
> ---
>  .../testing/selftests/net/af_unix/.gitignore  |   1 +
>  tools/testing/selftests/net/af_unix/Makefile  |   1 +
>  .../selftests/net/af_unix/unix_listen.c       | 126 ++++++++++++++++++
>  3 files changed, 128 insertions(+)
>  create mode 100644 tools/testing/selftests/net/af_unix/unix_listen.c
>
> diff --git a/tools/testing/selftests/net/af_unix/.gitignore b/tools/testing/selftests/net/af_unix/.gitignore
> index 240b26740c9e..973176644103 100644
> --- a/tools/testing/selftests/net/af_unix/.gitignore
> +++ b/tools/testing/selftests/net/af_unix/.gitignore
> @@ -6,3 +6,4 @@ scm_rights
>  so_peek_off
>  unix_connect
>  unix_connreset
> +unix_listen
> diff --git a/tools/testing/selftests/net/af_unix/Makefile b/tools/testing/selftests/net/af_unix/Makefile
> index 4c0375e28bbe..57d159803a3a 100644
> --- a/tools/testing/selftests/net/af_unix/Makefile
> +++ b/tools/testing/selftests/net/af_unix/Makefile
> @@ -14,6 +14,7 @@ TEST_GEN_PROGS := \
>         so_peek_off \
>         unix_connect \
>         unix_connreset \
> +       unix_listen \
>  # end of TEST_GEN_PROGS
>
>  include ../../lib.mk
> diff --git a/tools/testing/selftests/net/af_unix/unix_listen.c b/tools/testing/selftests/net/af_unix/unix_listen.c
> new file mode 100644
> index 000000000000..7b5264c97f52
> --- /dev/null
> +++ b/tools/testing/selftests/net/af_unix/unix_listen.c
> @@ -0,0 +1,126 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Tests for the state checks in AF_UNIX listen().
> + *
> + * The central case is a regression test: listen() on a bound socket that
> + * is already connected (i.e. not in TCP_CLOSE or TCP_LISTEN state) must
> + * fail with EINVAL.  A prior change accidentally let it return success
> + * without doing anything, because a helper called in between reset the
> + * error code to 0.  The neighbouring checks (unbound, already listening)
> + * are tested too so they cannot silently regress the same way.
> + */
> +#define _GNU_SOURCE
> +
> +#include <errno.h>
> +#include <stddef.h>
> +#include <string.h>
> +#include <unistd.h>
> +
> +#include <sys/socket.h>
> +#include <sys/un.h>
> +
> +#include "kselftest_harness.h"
> +
> +/* Fill @addr with an abstract-namespace address named @name. */
> +static socklen_t unix_abstract(struct sockaddr_un *addr, const char *name)
> +{
> +       size_t len = strlen(name);
> +
> +       memset(addr, 0, sizeof(*addr));
> +       addr->sun_family = AF_UNIX;
> +       /* Leading NUL selects the abstract namespace (no filesystem entry). */
> +       memcpy(addr->sun_path + 1, name, len);
> +
> +       return offsetof(struct sockaddr_un, sun_path) + 1 + len;
> +}
> +
> +FIXTURE(unix_listen)
> +{
> +       int sk;                 /* socket under test */
> +       int server;             /* a listening peer, when a test needs one */
> +       struct sockaddr_un addr, srv_addr;
> +       socklen_t addrlen, srv_addrlen;
> +};

Could you add test cases for SOCK_SEQPACKET and pathname
sockets ?  so it will be 4-patterns. see unix_connect.c


> +
> +FIXTURE_SETUP(unix_listen)
> +{
> +       self->sk = -1;
> +       self->server = -1;
> +       self->addrlen = unix_abstract(&self->addr, "unix_listen.sk");
> +       self->srv_addrlen = unix_abstract(&self->srv_addr, "unix_listen.srv");
> +}
> +
> +FIXTURE_TEARDOWN(unix_listen)
> +{
> +       if (self->sk >= 0)
> +               close(self->sk);
> +       if (self->server >= 0)
> +               close(self->server);
> +       /* Abstract addresses are released automatically on close. */
> +}
> +
> +/* A bound socket in TCP_CLOSE is the normal, allowed case. */
> +TEST_F(unix_listen, bound_is_ok)
> +{
> +       self->sk = socket(AF_UNIX, SOCK_STREAM, 0);
> +       ASSERT_LE(0, self->sk);
> +       ASSERT_EQ(0, bind(self->sk, (struct sockaddr *)&self->addr,
> +                         self->addrlen));

Personally I think this style is more readable:

err = func(...)
ASSERT_XX(val, err)


> +
> +       EXPECT_EQ(0, listen(self->sk, 8));
> +}
> +
> +/* Listening again on an already-listening socket (TCP_LISTEN) is allowed. */
> +TEST_F(unix_listen, relisten_is_ok)
> +{
> +       self->sk = socket(AF_UNIX, SOCK_STREAM, 0);
> +       ASSERT_LE(0, self->sk);
> +       ASSERT_EQ(0, bind(self->sk, (struct sockaddr *)&self->addr,
> +                         self->addrlen));
> +       ASSERT_EQ(0, listen(self->sk, 8));
> +
> +       EXPECT_EQ(0, listen(self->sk, 16));
> +}
> +
> +/* listen() on an unbound socket fails: there is nothing to listen on. */
> +TEST_F(unix_listen, unbound_is_einval)
> +{
> +       int ret;
> +
> +       self->sk = socket(AF_UNIX, SOCK_STREAM, 0);
> +       ASSERT_LE(0, self->sk);
> +
> +       ret = listen(self->sk, 8);
> +       EXPECT_EQ(-1, ret);
> +       EXPECT_EQ(EINVAL, errno);
> +}
> +
> +/*
> + * The regression: a bound socket that has already been connected is not in
> + * TCP_CLOSE or TCP_LISTEN, so listen() must reject it with EINVAL rather
> + * than quietly succeeding.
> + */
> +TEST_F(unix_listen, connected_is_einval)
> +{
> +       int ret;
> +
> +       self->server = socket(AF_UNIX, SOCK_STREAM, 0);
> +       ASSERT_LE(0, self->server);
> +       ASSERT_EQ(0, bind(self->server, (struct sockaddr *)&self->srv_addr,
> +                         self->srv_addrlen));
> +       ASSERT_EQ(0, listen(self->server, 8));
> +
> +       self->sk = socket(AF_UNIX, SOCK_STREAM, 0);
> +       ASSERT_LE(0, self->sk);
> +       /* Bind first so the unbound check does not mask the state check. */
> +       ASSERT_EQ(0, bind(self->sk, (struct sockaddr *)&self->addr,
> +                         self->addrlen));
> +       ASSERT_EQ(0, connect(self->sk, (struct sockaddr *)&self->srv_addr,
> +                            self->srv_addrlen));
> +
> +       ret = listen(self->sk, 8);
> +       EXPECT_EQ(-1, ret);
> +       EXPECT_EQ(EINVAL, errno);
> +}
> +
> +TEST_HARNESS_MAIN
> --
> 2.54.0
>