Re: [PATCH net v2 2/2] selftest: af_unix: Test scm_fds on dgram disconnect.

[Kuniyuki Iwashima <kuniyu@google.com>]

On Wed, 11 Nov 2026 22:51:48 +0000, Siddharth Chintamaneni wrote:
> Add dgram_disconnect_fdinfo in scm_rights.c verifying that scm_fds in
> /proc/self/fdinfo/<fd> returns to 0 when a connected SOCK_DGRAM socket
> with queued SCM_RIGHTS datagrams disconnects via connect(AF_UNSPEC) or
> observes a dead peer in send().
> 
> Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
> ---
>  .../selftests/net/af_unix/scm_rights.c        | 79 +++++++++++++++++++
>  1 file changed, 79 insertions(+)
> 
> diff --git a/tools/testing/selftests/net/af_unix/scm_rights.c b/tools/testing/selftests/net/af_unix/scm_rights.c
> index c165f250220a..ced83d3173b7 100644
> --- a/tools/testing/selftests/net/af_unix/scm_rights.c
> +++ b/tools/testing/selftests/net/af_unix/scm_rights.c
> @@ -395,4 +395,83 @@ TEST_F(scm_rights, mixed_lowpoint)
>  	close_sockets(6);
>  }
>  
> +static int count_scm_fds(struct __test_metadata *_metadata, int fd)
> +{
> +	char path[64], *line = NULL;
> +	int scm_fds = -1, ret;
> +	size_t unused = 0;
> +	FILE *f;
> +
> +	snprintf(path, sizeof(path), "/proc/self/fdinfo/%d", fd);
> +
> +	f = fopen(path, "r");
> +	ASSERT_NE(NULL, f);
> +
> +	while (getline(&line, &unused, f) != -1) {
> +		if (strncmp(line, "scm_fds:", 8))
> +			continue;
> +
> +		ret = sscanf(line + 8, "%d", &scm_fds);
> +		ASSERT_EQ(1, ret);
> +
> +		break;
> +	}
> +
> +	free(line);
> +
> +	ret = fclose(f);
> +	ASSERT_EQ(0, ret);
> +
> +	return scm_fds;
> +}
> +
> +TEST(dgram_disconnect_fdinfo)
> +{
> +	const FIXTURE_VARIANT(scm_rights) variant = {
> +		.name = "UNIX ",
> +		.type = SOCK_DGRAM,
> +	};
> +	FIXTURE_DATA(scm_rights) self = {};
> +	struct sockaddr addr = {
> +		.sa_family = AF_UNSPEC,
> +	};
> +	int ret;
> +
> +	ret = unshare(CLONE_NEWNET);
> +	ASSERT_EQ(0, ret);
> +	ASSERT_EQ(0, count_sockets(_metadata, &variant));

nit: count_sockets() is not needed.


> +
> +	create_socketpairs(_metadata, &self, &variant, 2);
> +
> +	/* 1. Disconnect via connect(AF_UNSPEC) */
> +	__send_fd(_metadata, &self, &variant, 0, 0);
> +	ASSERT_EQ(2, count_scm_fds(_metadata, self.fd[0]));
> +
> +	ret = connect(self.fd[0], &addr, sizeof(addr.sa_family));
> +	ASSERT_EQ(0, ret);
> +	ASSERT_EQ(0, count_scm_fds(_metadata, self.fd[0]));
> +
> +	/* 2. Dead-peer disconnect via send() */
> +	__send_fd(_metadata, &self, &variant, 1, 1);
> +	ASSERT_EQ(2, count_scm_fds(_metadata, self.fd[2]));
> +
> +	ret = close(self.fd[3]);
> +	ASSERT_EQ(0, ret);
> +
> +	ret = send(self.fd[2], "x", 1, 0);
> +	ASSERT_EQ(-1, ret);
> +	ASSERT_EQ(ECONNREFUSED, errno);
> +	ASSERT_EQ(0, count_scm_fds(_metadata, self.fd[2]));
> +
> +	ret = close(self.fd[0]);
> +	ASSERT_EQ(0, ret);
> +	ret = close(self.fd[1]);
> +	ASSERT_EQ(0, ret);
> +	ret = close(self.fd[2]);
> +	ASSERT_EQ(0, ret);
> +
> +	sleep(1);
> +	ASSERT_EQ(0, count_sockets(_metadata, &variant));

Same, these two lines are unnecessary.

sleep() and count_sockets() in FIXTURE_TEARDOWN(scm_rights)
were to wait GC to purge cyclic references, but this test does
not create that.


> +}
> +
>  TEST_HARNESS_MAIN
> -- 
> 2.43.0
>