Re: [PATCH net 2/2] vsock/test: add MSG_PEEK after partial recv test

[Arseniy Krasnov]

02.04.2026 11:18, Luigi Leonardi wrote:
> Add a test that verifies MSG_PEEK works correctly after a partial
> recv().
> 
> This is to test a bug that was present in the `virtio_transport_stream_do_peek()`
> when computing the number of bytes to copy: After a partial read, the
> peek function didn't take into consideration the number of bytes that
> were already read. So peeking the whole buffer would cause a out-of-bounds read,
> that resulted in a -EFAULT.
> 
> This test does exactly this: do a partial recv on a buffer, then try to
> peek the whole buffer content.
> 
> Signed-off-by: Luigi Leonardi <leonardi@xxxxxxxxxx>
> ---
>  tools/testing/vsock/vsock_test.c | 64 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 64 insertions(+)
> 
> diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
> index 5bd20ccd9335caafe68e8b7a5d02a4deb3d2deec..308f9f8f30d22bec5aaa282356e400d8438fe321 100644
> --- a/tools/testing/vsock/vsock_test.c
> +++ b/tools/testing/vsock/vsock_test.c
> @@ -346,6 +346,65 @@ static void test_stream_msg_peek_server(const struct test_opts *opts)
>  	return test_msg_peek_server(opts, false);
>  }
>  
> +#define PEEK_AFTER_RECV_LEN 100

Hi, may be we can just reuse MSG_PEEK_BUF_LEN which was already used in MSG_PEEK tests ?

Thanks

> +
> +static void test_stream_peek_after_recv_client(const struct test_opts *opts)
> +{
> +	unsigned char buf[PEEK_AFTER_RECV_LEN];
> +	int fd;
> +	int i;
> +
> +	fd = vsock_stream_connect(opts->peer_cid, opts->peer_port);
> +	if (fd < 0) {
> +		perror("connect");
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	for (i = 0; i < sizeof(buf); i++)
> +		buf[i] = (unsigned char)i;
> +
> +	control_expectln("SRVREADY");
> +
> +	send_buf(fd, buf, sizeof(buf), 0, sizeof(buf));
> +
> +	close(fd);
> +}
> +
> +static void test_stream_peek_after_recv_server(const struct test_opts *opts)
> +{
> +	unsigned char buf[PEEK_AFTER_RECV_LEN];
> +	int half = PEEK_AFTER_RECV_LEN / 2;
> +	ssize_t ret;
> +	int fd;
> +
> +	fd = vsock_stream_accept(VMADDR_CID_ANY, opts->peer_port, NULL);
> +	if (fd < 0) {
> +		perror("accept");
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	control_writeln("SRVREADY");
> +
> +	/* Partial recv to advance offset within the skb */
> +	recv_buf(fd, buf, half, 0, half);
> +
> +	/* Try to peek more than what remains: should return only 'half'
> +	 * bytes. Note: we can't use recv_buf() because it loops until
> +	 * all requested bytes are returned.
> +	 */
> +	ret = recv(fd, buf, sizeof(buf), MSG_PEEK);
> +	if (ret < 0) {
> +		perror("recv");
> +		exit(EXIT_FAILURE);
> +	} else if (ret != half) {
> +		fprintf(stderr, "MSG_PEEK after partial recv returned %d (expected %d)\n",
> +			ret, half);
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	close(fd);
> +}
> +
>  #define SOCK_BUF_SIZE (2 * 1024 * 1024)
>  #define SOCK_BUF_SIZE_SMALL (64 * 1024)
>  #define MAX_MSG_PAGES 4
> @@ -2520,6 +2579,11 @@ static struct test_case test_cases[] = {
>  		.run_client = test_stream_tx_credit_bounds_client,
>  		.run_server = test_stream_tx_credit_bounds_server,
>  	},
> +	{
> +		.name = "SOCK_STREAM MSG_PEEK after partial recv",
> +		.run_client = test_stream_peek_after_recv_client,
> +		.run_server = test_stream_peek_after_recv_server,
> +	},
>  	{},
>  };
>  
>