[PATCH net 1/2] wireguard: device: fix metadata_dst xmit null pointer dereference

[Jason A. Donenfeld]

Hi Nikolay,

On Thu, Apr 14, 2022 at 12:45 PM Nikolay Aleksandrov
<razor at blackwall.org> wrote:
> When we try to transmit an skb with md_dst attached through wireguard
> we hit a null pointer dereference[1] in wg_xmit() due to the use of
> dst_mtu() which calls into dst_blackhole_mtu() which in turn tries to
> dereference dst->dev. Since wireguard doesn't use md_dsts we should use
> skb_valid_dst() which checks for DST_METADATA flag and if it's set then
> fallback to wireguard's device mtu. That gives us the best chance of
> transmitting the packet, otherwise if the blackhole netdev is used we'd
> get ETH_MIN_MTU.

Thanks for the patch. Will queue up this patch #1 in the wireguard
tree and send it out to net.git not before too long.

Jason