[PATCH 4.19 07/25] net: check untrusted gso_size at kernel entry

[Greg Kroah-Hartman]

From: Willem de Bruijn <will...@google.com>

[ Upstream commit 6dd912f82680761d8fb6b1bb274a69d4c7010988 ]

Syzkaller again found a path to a kernel crash through bad gso input:
a packet with gso size exceeding len.

These packets are dropped in tcp_gso_segment and udp[46]_ufo_fragment.
But they may affect gso size calculations earlier in the path.

Now that we have thlen as of commit 9274124f023b ("net: stricter
validation of untrusted gso packets"), check gso_size at entry too.

Fixes: bfd5f4a3d605 ("packet: Add GSO/csum offload support.")
Reported-by: syzbot <syzkal...@googlegroups.com>
Signed-off-by: Willem de Bruijn <will...@google.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 include/linux/virtio_net.h |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -31,6 +31,7 @@ static inline int virtio_net_hdr_to_skb(
 {
        unsigned int gso_type = 0;
        unsigned int thlen = 0;
+       unsigned int p_off = 0;
        unsigned int ip_proto;
 
        if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
@@ -68,7 +69,8 @@ static inline int virtio_net_hdr_to_skb(
                if (!skb_partial_csum_set(skb, start, off))
                        return -EINVAL;
 
-               if (skb_transport_offset(skb) + thlen > skb_headlen(skb))
+               p_off = skb_transport_offset(skb) + thlen;
+               if (p_off > skb_headlen(skb))
                        return -EINVAL;
        } else {
                /* gso packets without NEEDS_CSUM do not set transport_offset.
@@ -92,17 +94,25 @@ retry:
                                return -EINVAL;
                        }
 
-                       if (keys.control.thoff + thlen > skb_headlen(skb) ||
+                       p_off = keys.control.thoff + thlen;
+                       if (p_off > skb_headlen(skb) ||
                            keys.basic.ip_proto != ip_proto)
                                return -EINVAL;
 
                        skb_set_transport_header(skb, keys.control.thoff);
+               } else if (gso_type) {
+                       p_off = thlen;
+                       if (p_off > skb_headlen(skb))
+                               return -EINVAL;
                }
        }
 
        if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
                u16 gso_size = __virtio16_to_cpu(little_endian, hdr->gso_size);
 
+               if (skb->len - p_off <= gso_size)
+                       return -EINVAL;
+
                skb_shinfo(skb)->gso_size = gso_size;
                skb_shinfo(skb)->gso_type = gso_type;