vhost/vsock: size receive SKBs from declared payload

vhost_vsock_alloc_skb() sizes the skb from iov_length(), the total guest
descriptor length.  virtio_transport_inc_rx_pkt() instead adds hdr->len to
rx_bytes and buf_used, and budgets each queued skb as SKB_TRUESIZE(0).  The
guest controls the descriptor length and hdr->len independently.

A guest can therefore provide a 64 KiB descriptor while declaring a zero
payload.  The descriptor-sized skb remains queued, rx_bytes and buf_used
remain unchanged, and only the fixed queue-entry budget limits retention.
This is not a lifetime leak: the skb is freed when dequeued or at socket
teardown.  Repeating this across connections can nevertheless exhaust host
memory.  On Linux v7.2, 455 such descriptors retained 30,255,680 bytes for
a 262,144-byte receive buffer; a full-payload control retained 265,984
bytes.

Vhost previously read hdr->len and allocated pkt->buf from that value.  The
conversion from virtio_vsock_pkt to sk_buff instead allocated receive skbs
from the descriptor length, introducing the allocation-accounting mismatch.

Copy the header into a stack object and validate hdr->len before allocating
the skb.  Size the allocation as sizeof(hdr) + payload_len so descriptor
capacity no longer determines queued memory.  Check payload_len against
len - sizeof(hdr) to avoid addition overflow on 32-bit hosts.

Fixes: 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff")
Cc: stable@vger.kernel.org
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://patch.msgid.link/20261004235101.1464007-1-4ncienth@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

0 files changed, 0 insertions, 0 deletions