netdev - Re: [PATCH net V2] net: ipv6: Validate GSO SKB before finish IPv6 processing

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Message-ID: <20210106155206.6f872e08@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 6 Jan 2021 15:52:06 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Aya Levin <ayal@...dia.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Axtens <dja@...ens.net>, netdev@...r.kernel.org,
        Moshe Shemesh <moshe@...lanox.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH net V2] net: ipv6: Validate GSO SKB before finish IPv6
 processing

On Tue,  5 Jan 2021 15:43:21 +0200 Aya Levin wrote:
> There are cases where GSO segment's length exceeds the egress MTU.

Please name same for posterity.

Please widen the CC list.

> If so:
>  - Consume the SKB and its segments.
>  - Issue an ICMP packet with 'Packet Too Big' message containing the
>    MTU, allowing the source host to reduce its Path MTU appropriately.
> 
> Note: These cases are handled in the same manner in IPv4 output finish.
> This patch aligns the behavior of IPv6 and the one of IPv4.
>
> Fixes: 9e50849054a4 ("netfilter: ipv6: move POSTROUTING invocation before fragmentation")

Not sure if this commit actually adds the problem or just moves the
problematic snippet around. But probably doesn't matter that much for
10+ years old code.

> Signed-off-by: Aya Levin <ayal@...dia.com>
> Reviewed-by: Tariq Toukan <tariqt@...dia.com>

The code itself looks reasonable AFAICT.