netdev - Re: [PATCH] net/xfrm: Fix lookups for states with spi == 0

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Message-ID: <1525264896.14025.23.camel@arista.com>
Date:   Wed, 02 May 2018 13:41:36 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     linux-kernel@...r.kernel.org, 0x7f454c46@...il.com,
        Steffen Klassert <steffen.klassert@...unet.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] net/xfrm: Fix lookups for states with spi == 0

On Wed, 2018-05-02 at 17:11 +0800, Herbert Xu wrote:
> On Wed, May 02, 2018 at 03:02:20AM +0100, Dmitry Safonov wrote:
> > It seems to be a valid use case to add xfrm state without
> > Security Parameter Indexes (SPI) value associated:
> > ip xfrm state add src $src dst $dst proto $proto mode $mode sel src
> > $src dst $dst $algo
> > 
> > The bad thing is that it's currently impossible to get/delete the
> > state
> > without SPI: __xfrm_state_insert() obviously doesn't add hash for
> > zero
> > SPI in xfrm.state_byspi, and xfrm_user_state_lookup() will fail as
> > xfrm_state_lookup() does lookups by hash.
> > 
> > It also isn't possible to workaround from userspace as
> > xfrm_id_proto_match() will be always true for ah/esp/comp protos.
> > 
> > So, don't try looking up by hash if SPI == 0.
> > 
> > Cc: Steffen Klassert <steffen.klassert@...unet.com>
> > Cc: Herbert Xu <herbert@...dor.apana.org.au>
> > Cc: "David S. Miller" <davem@...emloft.net>
> > Cc: netdev@...r.kernel.org
> > Signed-off-by: Dmitry Safonov <dima@...sta.com>
> 
> A zero SPI is illegal for many IPsec protocols because that value
> is used for other purposes, e.g., IKE encapsulation.

But still it's possible to create ipsec with zero SPI.
And it seems not making sense to search for a state with SPI hash if
request has zero SPI.

-- 
            Dima