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

[Stefano Garzarella <sgarzare@redhat.com>]

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@redhat.com>
>---
> 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@redhat.com>