xfrm: fix a warning in xfrm_policy_insert_list

This waring can be triggered simply by:

  # ip xfrm policy update src 192.168.1.1/24 dst 192.168.1.2/24 dir in \
    priority 1 mark 0 mask 0x10  #[1]
  # ip xfrm policy update src 192.168.1.1/24 dst 192.168.1.2/24 dir in \
    priority 2 mark 0 mask 0x1   #[2]
  # ip xfrm policy update src 192.168.1.1/24 dst 192.168.1.2/24 dir in \
    priority 2 mark 0 mask 0x10  #[3]

Then dmesg shows:

  [ ] WARNING: CPU: 1 PID: 7265 at net/xfrm/xfrm_policy.c:1548
  [ ] RIP: 0010:xfrm_policy_insert_list+0x2f2/0x1030
  [ ] Call Trace:
  [ ]  xfrm_policy_inexact_insert+0x85/0xe50
  [ ]  xfrm_policy_insert+0x4ba/0x680
  [ ]  xfrm_add_policy+0x246/0x4d0
  [ ]  xfrm_user_rcv_msg+0x331/0x5c0
  [ ]  netlink_rcv_skb+0x121/0x350
  [ ]  xfrm_netlink_rcv+0x66/0x80
  [ ]  netlink_unicast+0x439/0x630
  [ ]  netlink_sendmsg+0x714/0xbf0
  [ ]  sock_sendmsg+0xe2/0x110

The issue was introduced by Commit 7cb8a939 ("xfrm: Allow inserting
policies with matching mark and different priorities"). After that, the
policies [1] and [2] would be able to be added with different priorities.

However, policy [3] will actually match both [1] and [2]. Policy [1]
was matched due to the 1st 'return true' in xfrm_policy_mark_match(),
and policy [2] was matched due to the 2nd 'return true' in there. It
caused WARN_ON() in xfrm_policy_insert_list().

This patch is to fix it by only (the same value and priority) as the
same policy in xfrm_policy_mark_match().

Thanks to Yuehaibing, we could make this fix better.

v1->v2:
  - check policy->mark.v == pol->mark.v only without mask.

Fixes: 7cb8a939 ("xfrm: Allow inserting policies with matching mark and different priorities")
Reported-by: NXiumei Mu <xmu@redhat.com>
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_policy.c

@@ -1436,12 +1436,7 @@ static void xfrm_policy_requeue(struct xfrm_policy *old,
 static bool xfrm_policy_mark_match(struct xfrm_policy *policy,
 				   struct xfrm_policy *pol)
 {
-	u32 mark = policy->mark.v & policy->mark.m;
-
-	if (policy->mark.v == pol->mark.v && policy->mark.m == pol->mark.m)
-		return true;
-
-	if ((mark & pol->mark.m) == pol->mark.v &&
+	if (policy->mark.v == pol->mark.v &&
 	    policy->priority == pol->priority)
 		return true;