From: Willem de Bruijn <will...@google.com>
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 <syzkal...@googlegroups.com>
Signed-off-by: Willem de Bruijn <will...@google.com>
---
This captures a variety of bad gso packets, but to tighten further:
- drop SKB_GSO_DODGY packets with ipip/sit/.. , which cannot be legal.
by ipip_gso_segment wrappers around inet_gso_segment
expands on 121d57af308d ("gso: validate gso_type in GSO handlers")
- limit the number of ipv6 exthdrs allowed from dodgy sources.
not sure where to draw the line. but not at 64K ;)
- validate the network and transport protocol returned in
skb_probe_transport_header against the VIRTIO_NET_HDR_GSO type
- probe all dodgy GSO packets, also those that set checksum offload.
this will have a performance impact, discussed previously in
http://patchwork.ozlabs.org/patch/861874/
but it would have blocked this latest bug as well
All but the last one seem pretty uncontroversial to me. If no one
objects I plan to send those to net-next.
---
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 95d25b010a25..4c1c82a5678c 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2434,7 +2434,7 @@ static inline void skb_probe_transport_header(struct
sk_buff *skb,
if (skb_flow_dissect_flow_keys_basic(skb, &keys, NULL, 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);
}
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) {
--
2.21.0.rc0.258.g878e2cd30e-goog
