linux-kernel - Re: [PATCH net-next v4 3/3] vsock/test: Expand linger test to ensure close() does not misbehave

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Message-ID: <g5wemyogxthe43rkigufv7p5wrkegbdxbleujlsrk45dmbmm4l@qdynsbqfjwbk>
Date: Tue, 6 May 2025 11:43:10 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Michal Luczaj <mhal@...x.co>
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>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez <eperezma@...hat.com>, 
	Stefan Hajnoczi <stefanha@...hat.com>, virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH net-next v4 3/3] vsock/test: Expand linger test to ensure
 close() does not misbehave

On Thu, May 01, 2025 at 10:05:24AM +0200, Michal Luczaj wrote:
>There was an issue with SO_LINGER: instead of blocking until all queued
>messages for the socket have been successfully sent (or the linger timeout
>has been reached), close() would block until packets were handled by the
>peer.

This is a new behaviour that only new kernels will follow, so I think
it is better to add a new test instead of extending a pre-existing test
that we described as "SOCK_STREAM SO_LINGER null-ptr-deref".

The old test should continue to check the null-ptr-deref also for old
kernels, while the new test will check the new behaviour, so we can skip
the new test while testing an old kernel.

Thanks,
Stefano

>
>Add a check to alert on close() lingering when it should not.
>
>Signed-off-by: Michal Luczaj <mhal@...x.co>
>---
> tools/testing/vsock/vsock_test.c | 30 +++++++++++++++++++++++++++---
> 1 file changed, 27 insertions(+), 3 deletions(-)
>
>diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
>index d0f6d253ac72d08a957cb81a3c38fcc72bec5a53..82d0bc20dfa75041f04eada1b4310be2f7c3a0c1 100644
>--- a/tools/testing/vsock/vsock_test.c
>+++ b/tools/testing/vsock/vsock_test.c
>@@ -1788,13 +1788,16 @@ static void test_stream_connect_retry_server(const struct test_opts *opts)
> 	close(fd);
> }
>
>+#define	LINGER_TIMEOUT	1	/* seconds */
>+
> static void test_stream_linger_client(const struct test_opts *opts)
> {
> 	struct linger optval = {
> 		.l_onoff = 1,
>-		.l_linger = 1
>+		.l_linger = LINGER_TIMEOUT
> 	};
>-	int fd;
>+	int bytes_unsent, fd;
>+	time_t ts;
>
> 	fd = vsock_stream_connect(opts->peer_cid, opts->peer_port);
> 	if (fd < 0) {
>@@ -1807,7 +1810,28 @@ static void test_stream_linger_client(const struct test_opts *opts)
> 		exit(EXIT_FAILURE);
> 	}
>
>+	/* Byte left unread to expose any incorrect behaviour. */
>+	send_byte(fd, 1, 0);
>+
>+	/* Reuse LINGER_TIMEOUT to wait for bytes_unsent == 0. */
>+	timeout_begin(LINGER_TIMEOUT);
>+	do {
>+		if (ioctl(fd, SIOCOUTQ, &bytes_unsent) < 0) {
>+			perror("ioctl(SIOCOUTQ)");
>+			exit(EXIT_FAILURE);
>+		}
>+		timeout_check("ioctl(SIOCOUTQ) == 0");
>+	} while (bytes_unsent != 0);
>+	timeout_end();
>+
>+	ts = current_nsec();
> 	close(fd);
>+	if ((current_nsec() - ts) / NSEC_PER_SEC > 0) {
>+		fprintf(stderr, "Unexpected lingering on close()\n");
>+		exit(EXIT_FAILURE);
>+	}
>+
>+	control_writeln("DONE");
> }
>
> static void test_stream_linger_server(const struct test_opts *opts)
>@@ -1820,7 +1844,7 @@ static void test_stream_linger_server(const struct test_opts *opts)
> 		exit(EXIT_FAILURE);
> 	}
>
>-	vsock_wait_remote_close(fd);
>+	control_expectln("DONE");
> 	close(fd);
> }
>
>
>-- 
>2.49.0
>