[PATCH 5.4 10/34] net: check untrusted gso_size at kernel entry

Greg Kroah-Hartman
2020-06-09T18:04:54Z

From: Willem de Bruijn <willemb@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 <syzkaller@googlegroups.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@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;