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

Luigi Leonardi
2026-04-14T16:10:35Z

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.

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

--
2.53.0