Subject: [PATCH 02/11] xfrm: skip policies marked as dead while rehashing

From: Steffen Klassert <[email-masked]>
Date: Thu, 11 Jan 2018 12:37:37 +0100

From: Florian Westphal <[email-masked]>

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 <[email-masked]>
Cc: Timo Teras <[email-masked]>
Cc: Christophe Gouault <[email-masked]>
Reported-by: syzbot <[email-masked]>
Signed-off-by: Florian Westphal <[email-masked]>
Signed-off-by: Steffen Klassert <[email-masked]>
---
 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 70aa5cb0c659..2ef6db98e9ba 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;
 		}
-- 
2.14.1