tap: add missing verification for short frame

JIRA: https://issues.redhat.com/browse/RHEL-50265
CVE: CVE-2024-41090
Upstream Status: Posted https://lore.kernel.org/all/20240724170452.16837-2-dongli.zhang@oracle.com/

Author: Si-Wei Liu <si-wei.liu@oracle.com>
Date:   Wed Jul 24 10:04:51 2024 -0700

    tap: add missing verification for short frame

    The cited commit missed to check against the validity of the frame length
    in the tap_get_user_xdp() path, which could cause a corrupted skb to be
    sent downstack. Even before the skb is transmitted, the
    tap_get_user_xdp()-->skb_set_network_header() may assume the size is more
    than ETH_HLEN. Once transmitted, this could either cause out-of-bound
    access beyond the actual length, or confuse the underlayer with incorrect
    or inconsistent header length in the skb metadata.

    In the alternative path, tap_get_user() already prohibits short frame which
    has the length less than Ethernet header size from being transmitted.

    This is to drop any frame shorter than the Ethernet header size just like
    how tap_get_user() does.

    CVE: CVE-2024-41090
    Link: https://lore.kernel.org/netdev/1717026141-25716-1-git-send-email-si-wei.liu@oracle.com/
    Fixes: 0efac27 ("tap: accept an array of XDP buffs through sendmsg()")
    Cc: stable@vger.kernel.org
    Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
    Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
    Reviewed-by: Willem de Bruijn <willemb@google.com>
    Reviewed-by: Paolo Abeni <pabeni@redhat.com>
    Reviewed-by: Jason Wang <jasowang@redhat.com>

Signed-off-by: Patrick Talbert <ptalbert@redhat.com>

Author: ptalbert

drivers/net/tap.c

@@ -1157,6 +1157,11 @@ static int tap_get_user_xdp(struct tap_queue *q, struct xdp_buff *xdp)
 	struct sk_buff *skb;
 	int err, depth;
 
+	if (unlikely(xdp->data_end - xdp->data < ETH_HLEN)) {
+		err = -EINVAL;
+		goto err;
+	}
+
 	if (q->flags & IFF_VNET_HDR)
 		vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);