linux-kernel - Re: [PATCH] netfilter: Fix remainder of pseudo-header protocol 0

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Message-ID: <20190627184903.atdcwk4wnfaayyer@salvia>
Date:   Thu, 27 Jun 2019 20:49:03 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     zhe.he@...driver.com
Cc:     kadlec@...ckhole.kfki.hu, fw@...len.de, davem@...emloft.net,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netfilter: Fix remainder of pseudo-header protocol 0

On Mon, Jun 24, 2019 at 11:17:38AM +0800, zhe.he@...driver.com wrote:
> From: He Zhe <zhe.he@...driver.com>
> 
> Since v5.1-rc1, some types of packets do not get unreachable reply with the
> following iptables setting. Fox example,
> 
> $ iptables -A INPUT -p icmp --icmp-type 8 -j REJECT
> $ ping 127.0.0.1 -c 1
> PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.
> — 127.0.0.1 ping statistics —
> 1 packets transmitted, 0 received, 100% packet loss, time 0ms
> 
> We should have got the following reply from command line, but we did not.
> From 127.0.0.1 icmp_seq=1 Destination Port Unreachable
> 
> Yi Zhao reported it and narrowed it down to:
> 7fc38225363d ("netfilter: reject: skip csum verification for protocols that don't support it"),
> 
> This is because nf_ip_checksum still expects pseudo-header protocol type 0 for
> packets that are of neither TCP or UDP, and thus ICMP packets are mistakenly
> treated as TCP/UDP.
> 
> This patch corrects the conditions in nf_ip_checksum and all other places that
> still call it with protocol 0.

Looking at 7fc38225363dd8f19e667ad7c77b63bc4a5c065d, I wonder this can
be fixed while simplifying it...

I think nf_reject_verify_csum() is useless?

In your patch, now you explicitly check for IPPROTO_TCP and
IPPROTO_UDP to validate the checksum.