vsock/test: add MSG_PEEK after partial recv test

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. The test re-uses
`test_stream_msg_peek_client()` to also cover this scenario.

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Luigi Leonardi <leonardi@redhat.com>
Link: https://patch.msgid.link/20260415-fix_peek-v4-3-8207e872759e@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index bdb0754965df..76be0e4a7f0e 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);
+
+	/* Peek with a buffer larger than the remaining data */
+	recv_buf(fd, buf_peek, sizeof(buf_peek), MSG_PEEK, sizeof(buf_peek) - 1);
+
+	/* 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,
+	},
 	{},
 };