Patch "xfrm: skip policies marked as dead while rehashing" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

xfrm: skip policies marked as dead while rehashing

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xfrm-skip-policies-marked-as-dead-while-rehashing.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Florian Westphal <[email protected]>
Date: Wed, 27 Dec 2017 23:25:45 +0100
Subject: xfrm: skip policies marked as dead while rehashing

From: Florian Westphal <[email protected]>

commit 862591bf4f519d1b8d859af720fafeaebdd0162a upstream.

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).

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

@@ -643,7 +643,8 @@ static void xfrm_hash_rebuild(struct wor
 
 	/* 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;
 		}

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/xfrm-skip-policies-marked-as-dead-while-rehashing.patch queue-4.9/netfilter-x_tables-avoid-out-of-bounds-reads-in-xt_request_find_-match-target.patch queue-4.9/netfilter-on-sockopt-acquire-sock-lock-only-in-the-required-scope.patch queue-4.9/netfilter-xt_rateest-acquire-xt_rateest_mutex-for-hash-insert.patch