4.9-stable review patch. If anyone has any objections, please let me know.
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From: Willem de Bruijn willemb@google.com
[ Upstream commit d5be7f632bad0f489879eed0ff4b99bd7fe0b74c ]
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: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 @@ -2204,7 +2204,7 @@ static inline void skb_probe_transport_h 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); }
--- a/include/linux/virtio_net.h +++ b/include/linux/virtio_net.h @@ -38,6 +38,15 @@ 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) {