[PATCH net v3 1/3] vsock/virtio: fix MSG_PEEK ignoring skb offset when calculating bytes to copy

[Luigi Leonardi <leonardi@redhat.com>]

`virtio_transport_stream_do_peek()` does not account for the skb offset
when computing the number of bytes to copy.

This means that, after a partial recv() that advances the offset, a peek
requesting more bytes than are available in the sk_buff causes
`skb_copy_datagram_iter()` to go past the valid payload, resulting in
a -EFAULT.

The dequeue path already handles this correctly.
Apply the same logic to the peek path.

Fixes: 0df7cd3c13e4 ("vsock/virtio/vhost: read data from non-linear skb")
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
Signed-off-by: Luigi Leonardi <leonardi@redhat.com>
---
 net/vmw_vsock/virtio_transport_common.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index a152a9e208d0..b5015ab2ee1e 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -545,9 +545,8 @@ virtio_transport_stream_do_peek(struct vsock_sock *vsk,
 	skb_queue_walk(&vvs->rx_queue, skb) {
 		size_t bytes;
 
-		bytes = len - total;
-		if (bytes > skb->len)
-			bytes = skb->len;
+		bytes = min_t(size_t, len - total,
+			      skb->len - VIRTIO_VSOCK_SKB_CB(skb)->offset);
 
 		spin_unlock_bh(&vvs->rx_lock);
 

-- 
2.53.0