netdev - Re: [PATCH net] net: ipv4: don't allow setting net.ipv4.route.min

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Message-Id: <20180227.111359.2169847516477802515.davem@davemloft.net>
Date:   Tue, 27 Feb 2018 11:13:59 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     sd@...asysnail.net
Cc:     netdev@...r.kernel.org, jishi@...hat.com, sbrivio@...hat.com
Subject: Re: [PATCH net] net: ipv4: don't allow setting
 net.ipv4.route.min_pmtu below 68

From: Sabrina Dubroca <sd@...asysnail.net>
Date: Mon, 26 Feb 2018 16:13:43 +0100

> According to RFC 1191 sections 3 and 4, ICMP frag-needed messages
> indicating an MTU below 68 should be rejected:
> 
>     A host MUST never reduce its estimate of the Path MTU below 68
>     octets.
> 
> and (talking about ICMP frag-needed's Next-Hop MTU field):
> 
>     This field will never contain a value less than 68, since every
>     router "must be able to forward a datagram of 68 octets without
>     fragmentation".
> 
> Furthermore, by letting net.ipv4.route.min_pmtu be set to negative
> values, we can end up with a very large PMTU when (-1) is cast into u32.
> 
> Let's also make ip_rt_min_pmtu a u32, since it's only ever compared to
> unsigned ints.
> 
> Reported-by: Jianlin Shi <jishi@...hat.com>
> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
> Reviewed-by: Stefano Brivio <sbrivio@...hat.com>

Applied and queued up for -stable, thanks Sabrina.