[PATCH 4.4 076/105] xfrm: skip policies marked as dead while rehashing

From: Greg Kroah-Hartman
Date: Sun Jul 01 2018 - 12:19:53 EST

4.4-stable review patch. If anyone has any objections, please let me know.


From: Florian Westphal <fw@xxxxxxxxx>

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).

Fixes: 880a6fab8f6ba5b ("xfrm: configure policy hash table thresholds by netlink")
Fixes: 12a169e7d8f4b1c ("ipsec: Put dumpers on the dump list")
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: Timo Teras <timo.teras@xxxxxx>
Cc: Christophe Gouault <christophe.gouault@xxxxxxxxx>
Reported-by: syzbot <bot+c028095236fcb6f4348811565b75084c754dc729@xxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Cc: Zubin Mithra <zsm@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -626,7 +626,8 @@ 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 */