From: Willem de Bruijn <willemb@google.com>
Date: Fri, 15 Feb 2019 12:15:47 -0500
Subject: net: validate untrusted gso packets without csum offload
Git-commit: d5be7f632bad0f489879eed0ff4b99bd7fe0b74c
Patch-mainline: v5.0-rc8
References: networking-stable-19_02_20
Syzkaller again found a path to a kernel crash through bad gso input.
By building an excessively large packet to cause an skb field to wrap.
If VIRTIO_NET_HDR_F_NEEDS_CSUM was set this would have been dropped in
skb_partial_csum_set.
GSO packets that do not set checksum offload are suspicious and rare.
Most callers of virtio_net_hdr_to_skb already pass them to
skb_probe_transport_header.
Move that test forward, change it to detect parse failure and drop
packets on failure as those cleary are not one of the legitimate
VIRTIO_NET_HDR_GSO types.
Fixes: bfd5f4a3d605 ("packet: Add GSO/csum offload support.")
Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
include/linux/skbuff.h | 2 +-
include/linux/virtio_net.h | 9 +++++++++
2 files changed, 10 insertions(+), 1 deletion(-)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2256,7 +2256,7 @@ static inline void skb_probe_transport_h
if (skb_flow_dissect_flow_keys_basic(skb, &keys, 0, 0, 0, 0, 0))
skb_set_transport_header(skb, keys.control.thoff);
- else
+ else if (offset_hint >= 0)
skb_set_transport_header(skb, offset_hint);
}
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -56,6 +56,15 @@ static inline int virtio_net_hdr_to_skb(
if (!skb_partial_csum_set(skb, start, off))
return -EINVAL;
+ } else {
+ /* gso packets without NEEDS_CSUM do not set transport_offset.
+ * probe and drop if does not match one of the above types.
+ */
+ if (gso_type) {
+ skb_probe_transport_header(skb, -1);
+ if (!skb_transport_header_was_set(skb))
+ return -EINVAL;
+ }
}
if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {