netdev - Re: [PATCH net 1/2] wireguard: device: fix metadata

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Message-ID: <CAHmME9qZyz26gnfcZCjAiLhYqZ9LwJN1VZ+3rgGmhxJYrGvZCw@mail.gmail.com>
Date:   Thu, 14 Apr 2022 13:58:04 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Nikolay Aleksandrov <razor@...ckwall.org>
Cc:     Netdev <netdev@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martynas Pumputis <m@...bda.lt>,
        WireGuard mailing list <wireguard@...ts.zx2c4.com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH net 1/2] wireguard: device: fix metadata_dst xmit null
 pointer dereference

Hi Nikolay,

On Thu, Apr 14, 2022 at 12:45 PM Nikolay Aleksandrov
<razor@...ckwall.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