Patch "net: virtio_net_hdr_to_skb: count transport header in UFO" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    net: virtio_net_hdr_to_skb: count transport header in UFO

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-virtio_net_hdr_to_skb-count-transport-header-in-.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 3b076aa2c87e3f8db9e19311d4b9f35c4f95cf85
Author: Jonathan Davies <jonathan.davies@xxxxxxxxxxx>
Date:   Tue Nov 16 17:42:42 2021 +0000

    net: virtio_net_hdr_to_skb: count transport header in UFO
    
    [ Upstream commit cf9acc90c80ecbee00334aa85d92f4e74014bcff ]
    
    virtio_net_hdr_to_skb does not set the skb's gso_size and gso_type
    correctly for UFO packets received via virtio-net that are a little over
    the GSO size. This can lead to problems elsewhere in the networking
    stack, e.g. ovs_vport_send dropping over-sized packets if gso_size is
    not set.
    
    This is due to the comparison
    
      if (skb->len - p_off > gso_size)
    
    not properly accounting for the transport layer header.
    
    p_off includes the size of the transport layer header (thlen), so
    skb->len - p_off is the size of the TCP/UDP payload.
    
    gso_size is read from the virtio-net header. For UFO, fragmentation
    happens at the IP level so does not need to include the UDP header.
    
    Hence the calculation could be comparing a TCP/UDP payload length with
    an IP payload length, causing legitimate virtio-net packets to have
    lack gso_type/gso_size information.
    
    Example: a UDP packet with payload size 1473 has IP payload size 1481.
    If the guest used UFO, it is not fragmented and the virtio-net header's
    flags indicate that it is a GSO frame (VIRTIO_NET_HDR_GSO_UDP), with
    gso_size = 1480 for an MTU of 1500.  skb->len will be 1515 and p_off
    will be 42, so skb->len - p_off = 1473.  Hence the comparison fails, and
    shinfo->gso_size and gso_type are not set as they should be.
    
    Instead, add the UDP header length before comparing to gso_size when
    using UFO. In this way, it is the size of the IP payload that is
    compared to gso_size.
    
    Fixes: 6dd912f82680 ("net: check untrusted gso_size at kernel entry")
    Signed-off-by: Jonathan Davies <jonathan.davies@xxxxxxxxxxx>
    Reviewed-by: Willem de Bruijn <willemb@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index b465f8f3e554f..04e87f4b9417c 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -120,10 +120,15 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
 
 	if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
 		u16 gso_size = __virtio16_to_cpu(little_endian, hdr->gso_size);
+		unsigned int nh_off = p_off;
 		struct skb_shared_info *shinfo = skb_shinfo(skb);
 
+		/* UFO may not include transport header in gso_size. */
+		if (gso_type & SKB_GSO_UDP)
+			nh_off -= thlen;
+
 		/* Too small packets are not really GSO ones. */
-		if (skb->len - p_off > gso_size) {
+		if (skb->len - nh_off > gso_size) {
 			shinfo->gso_size = gso_size;
 			shinfo->gso_type = gso_type;