netdev - Re: [PATCH] xfrm: Fix wraparound in xfrm_policy_addr

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Date:   Wed, 30 Dec 2020 13:46:19 +0100
From:   Florian Westphal <fw@...len.de>
To:     Visa Hankala <visa@...kala.org>
Cc:     Florian Westphal <fw@...len.de>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] xfrm: Fix wraparound in xfrm_policy_addr_delta()

Visa Hankala <visa@...kala.org> wrote:
> On Tue, Dec 29, 2020 at 05:01:27PM +0100, Florian Westphal wrote:
> > This is suspicious.  Is prefixlen == 0 impossible?
> > 
> > If not, then after patch
> > mask = ~0U << 32;
> > 
> > ... and function returns 0.
> 
> With prefixlen == 0, there is only one equivalence class, so
> returning 0 seems reasonable to me.

Right, that seems reasonable indeed.

> Is there a reason why the function has treated /0 prefix as /32
> with IPv4? IPv6 does not have this treatment.

Not that I recall, looks like a bug.