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 <herb...@gondor.apana.org.au>
> > Cc: Timo Teras <timo.te...@iki.fi>
> > Cc: Christophe Gouault <christophe.goua...@6wind.com>
> > Reported-by: syzbot
> > <bot+c028095236fcb6f4348811565b75084c754dc...@syzkaller.appspotmail.com>
> > Signed-off-by: Florian Westphal <f...@strlen.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
