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

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Message-Id: <20171227222545.22219-1-fw@strlen.de>
Date:   Wed, 27 Dec 2017 23:25:45 +0100
From:   Florian Westphal <fw@...len.de>
To:     <netdev@...r.kernel.org>
Cc:     steffen.klassert@...unet.com, syzkaller-bugs@...glegroups.com,
        Florian Westphal <fw@...len.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Timo Teras <timo.teras@....fi>,
        Christophe Gouault <christophe.gouault@...nd.com>
Subject: [PATCH ipsec] xfrm: skip policies marked as dead while rehashing

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>
---
 net/xfrm/xfrm_policy.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 9542975eb2f9..181bc6181789 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -609,7 +609,8 @@ static void xfrm_hash_rebuild(struct work_struct *work)
 
 	/* re-insert all policies by order of creation */
 	list_for_each_entry_reverse(policy, &net->xfrm.policy_all, walk.all) {
-		if (xfrm_policy_id2dir(policy->index) >= XFRM_POLICY_MAX) {
+		if (policy->walk.dead ||
+		    xfrm_policy_id2dir(policy->index) >= XFRM_POLICY_MAX) {
 			/* skip socket policies */
 			continue;
 		}
-- 
2.13.6