netdev - Re: [PATCH ipsec] xfrm: skip policies marked as dead while rehashing

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Message-ID: <20180131015954.vdcywjiga6idam53@gmail.com>
Date:   Tue, 30 Jan 2018 17:59:54 -0800
From:   Eric Biggers <ebiggers3@...il.com>
To:     Steffen Klassert <steffen.klassert@...unet.com>
Cc:     Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Timo Teras <timo.teras@....fi>,
        Christophe Gouault <christophe.gouault@...nd.com>
Subject: Re: [PATCH ipsec] xfrm: skip policies marked as dead while rehashing

On Sun, Dec 31, 2017 at 08:50:17AM +0100, Steffen Klassert wrote:
> On Wed, Dec 27, 2017 at 11:25:45PM +0100, Florian Westphal wrote:
> > syzkaller triggered following KASAN splat:
> > 
> > BUG: KASAN: slab-out-of-bounds in xfrm_hash_rebuild+0xdbe/0xf00 net/xfrm/xfrm_policy.c:618
> > read of size 2 at addr ffff8801c8e92fe4 by task kworker/1:1/23 [..]
> > Workqueue: events xfrm_hash_rebuild [..]
> >  __asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:428
> >  xfrm_hash_rebuild+0xdbe/0xf00 net/xfrm/xfrm_policy.c:618
> >  process_one_work+0xbbf/0x1b10 kernel/workqueue.c:2112
> >  worker_thread+0x223/0x1990 kernel/workqueue.c:2246 [..]
> > 
> > The reproducer triggers:
> > 1016                 if (error) {
> > 1017                         list_move_tail(&walk->walk.all, &x->all);
> > 1018                         goto out;
> > 1019                 }
> > 
> > in xfrm_policy_walk() via pfkey (it sets tiny rcv space, dump
> > callback returns -ENOBUFS).
> > 
> > In this case, *walk is located the pfkey socket struct, so this socket
> > becomes visible in the global policy list.
> > 
> > It looks like this is intentional -- phony walker has walk.dead set to 1
> > and all other places skip such "policies".
> > 
> > Ccing original authors of the two commits that seem to expose this
> > issue (first patch missed ->dead check, second patch adds pfkey
> > sockets to policies dumper list).
> > 
> > Fixes: 880a6fab8f6ba5b ("xfrm: configure policy hash table thresholds by netlink")
> > Fixes: 12a169e7d8f4b1c ("ipsec: Put dumpers on the dump list")
> > Cc: Herbert Xu <herbert@...dor.apana.org.au>
> > Cc: Timo Teras <timo.teras@....fi>
> > Cc: Christophe Gouault <christophe.gouault@...nd.com>
> > Reported-by: syzbot <bot+c028095236fcb6f4348811565b75084c754dc729@...kaller.appspotmail.com>
> > Signed-off-by: Florian Westphal <fw@...len.de>
> 
> Applied, thanks a lot!
> 

This crash seems to have stopped occurring, thanks Florian!  Let's tell syzbot
so that it can start reporting any crashes in this same place again:

#syz fix: xfrm: skip policies marked as dead while rehashing

- Eric