Re: [PATCH net v3 3/3] vsock/test: add MSG_PEEK after partial recv test

[Stefano Garzarella]

On Tue, Apr 14, 2026 at 06:10:23PM +0200, 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 an 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.

nit: I think it's better to mention also that we are re-using
test_stream_msg_peek_client() also for this test.

> Signed-off-by: Luigi Leonardi <leonardi@xxxxxxxxxx>
> ---
> tools/testing/vsock/vsock_test.c | 37 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 37 insertions(+)
>
> diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
> index bdb0754965df..ab387a13f0ae 100644
> --- a/tools/testing/vsock/vsock_test.c
> +++ b/tools/testing/vsock/vsock_test.c
> @@ -346,6 +346,38 @@ static void test_stream_msg_peek_server(const struct test_opts *opts)
> 	return test_msg_peek_server(opts, false);
> }
>
> +static void test_stream_peek_after_recv_server(const struct test_opts *opts)
> +{
> +	unsigned char buf_normal[MSG_PEEK_BUF_LEN];
> +	unsigned char buf_peek[MSG_PEEK_BUF_LEN];
> +	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_normal, 1, 0, 1);
> +
> +	/* Ask more bytes than available */

nit:	/* Peek with a buffer larger than the remaining data */

> +	recv_buf(fd, buf_peek, sizeof(buf_peek), MSG_PEEK, sizeof(buf_peek) - 1);
> +
> +	/* Recv rest of the data */

nit:	/* Consume the remaining data */

> +	recv_buf(fd, buf_normal, sizeof(buf_normal) - 1, 0, sizeof(buf_normal) - 1);
> +
> +	/* Compare full peek and normal read. */
> +	if (memcmp(buf_peek, buf_normal, sizeof(buf_peek) - 1)) {
> +		fprintf(stderr, "Full peek data mismatch\n");
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	close(fd);
> +}
> +
> #define SOCK_BUF_SIZE (2 * 1024 * 1024)
> #define SOCK_BUF_SIZE_SMALL (64 * 1024)
> #define MAX_MSG_PAGES 4
> @@ -2509,6 +2541,11 @@ 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_msg_peek_client,
> +		.run_server = test_stream_peek_after_recv_server,

I left just minor comments, the test LGTM:

Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>