Re: [PATCH net v2 3/3] vsock/test: add MSG_PEEK after partial recv test

[Stefano Garzarella]

On Tue, Apr 07, 2026 at 11:13:57AM +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 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 <leona...@redhat.com>
---
tools/testing/vsock/vsock_test.c | 43 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 43 insertions(+)

diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index bdb0754965df..d38a90a86f34 100644
--- a/tools/testing/vsock/vsock_test.c
+++ b/tools/testing/vsock/vsock_test.c
@@ -346,6 +346,44 @@ 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_client(const struct test_opts *opts)
+{
+       unsigned char buf[MSG_PEEK_BUF_LEN];

What about:

        unsigned char buf[MSG_PEEK_BUF_LEN] = { 0 };

so we can remove the memset() call?

+       int fd;
+
+       fd = vsock_stream_connect(opts->peer_cid, opts->peer_port);
+       if (fd < 0) {
+               perror("connect");
+               exit(EXIT_FAILURE);
+       }
+
+       memset(buf, 0, sizeof(buf));
+
+       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[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);
+       }
+
+       /* Partial recv to advance offset within the skb */
+       recv_buf(fd, buf, 1, 0, 1);
+
+       /* Ask more bytes than available */
+       recv_buf(fd, buf, sizeof(buf), MSG_PEEK, sizeof(buf) - 1);

What about checking also what we read like we do in 
test_msg_peek_server() ?

Not a strong opinion, but if we go in that direction, maybe we can just 
reuse test_stream_msg_peek_client() also for this test case.

Thanks,
Stefano

+
+       close(fd);
+}
+
#define SOCK_BUF_SIZE (2 * 1024 * 1024)
#define SOCK_BUF_SIZE_SMALL (64 * 1024)
#define MAX_MSG_PAGES 4
@@ -2509,6 +2547,11 @@ 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,
+       },
        {},
};


--
2.53.0