netdev - Re: [syzbot] [net?] UBSAN: shift-out-of-bounds in xfrm_selector

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Message-ID: <Zvws-45NVXIMUYl4@hog>
Date: Tue, 1 Oct 2024 19:10:19 +0200
From: Sabrina Dubroca <sd@...asysnail.net>
To: Steffen Klassert <steffen.klassert@...unet.com>
Cc: pabeni@...hat.com,
	syzbot <syzbot+cc39f136925517aed571@...kaller.appspotmail.com>,
	davem@...emloft.net, edumazet@...gle.com,
	herbert@...dor.apana.org.au, kuba@...nel.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] UBSAN: shift-out-of-bounds in
 xfrm_selector_match (2)

Hi Steffen,

2024-09-27, 10:38:13 +0200, Sabrina Dubroca wrote:
> 2024-09-27, 09:30:09 +0200, Steffen Klassert wrote:
> > On Wed, Sep 25, 2024 at 01:08:48PM +0200, Sabrina Dubroca wrote:
> > > Maybe a check for prefixlen < 128 would also be useful in the
> > > XFRM_STATE_AF_UNSPEC case, to avoid the same problems with syzbot
> > > passing prefixlen=200 for an ipv6 SA. I don't know how
> > > XFRM_STATE_AF_UNSPEC is used, so I'm not sure what restrictions we can
> > > put. If we end up with prefixlen = 100 used from ipv4 we'll still have
> > > the same issues.
> > 
> > I've introduced XFRM_STATE_AF_UNSPEC back in 2008 to make
> > inter addressfamily tunnels working while maintaining
> > backwards compatibility to openswan that did not set
> > the selector family. At least that's what I found in
> > an E-Mail conversation from back then.
> > 
> > A check for prefixlen <= 128 would make sense in any case.
> > But not sure if we can restrict that somehow further.
> 
> I'll add this check too, and then I'll run some more experiments with
> that flag.

I ended up not adding the check, since for x->sel.family == AF_UNSPEC,
xfrm_state_look_at doesn't use the selector at all, so I don't think
restricting prefixlen in that case would do anything.

-- 
Sabrina