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

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Date:   Sun, 31 Dec 2017 08:50:17 +0100
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Florian Westphal <fw@...len.de>
CC:     <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 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!