From dac7d4432b13d6b58923c1178b786bcda37c9e9e Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Fri, 15 Feb 2019 12:15:47 -0500 Subject: [PATCH] net: validate untrusted gso packets without csum offload commit d5be7f632bad0f489879eed0ff4b99bd7fe0b74c upstream. 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 Signed-off-by: Willem de Bruijn Reviewed-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/linux/skbuff.h | 2 +- include/linux/virtio_net.h | 9 +++++++++ 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 50a4a5968f3a..3172e14d9398 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -2377,7 +2377,7 @@ static inline void skb_probe_transport_header(struct sk_buff *skb, return; else if (skb_flow_dissect_flow_keys(skb, &keys, 0)) skb_set_transport_header(skb, keys.control.thoff); - else + else if (offset_hint >= 0) skb_set_transport_header(skb, offset_hint); } diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h index cb462f9ab7dd..71f2394abbf7 100644 --- a/include/linux/virtio_net.h +++ b/include/linux/virtio_net.h @@ -57,6 +57,15 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *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) { -- 2.20.1