xfrm: policy: fix policy hash rebuild

Dan Carpenter reports following static checker warning:
 net/xfrm/xfrm_policy.c:1316 xfrm_hash_rebuild()
 warn: 'dir' is out of bounds '3' vs '2'

 |  1280          /* reset the bydst and inexact table in all directions */
 |  1281          xfrm_hash_reset_inexact_table(net);
 |  1282
 |  1283          for (dir = 0; dir < XFRM_POLICY_MAX; dir++) {
 |                              ^^^^^^^^^^^^^^^^^^^^^
 |dir == XFRM_POLICY_MAX at the end of this loop.
 |  1304          /* re-insert all policies by order of creation */
 |  1305          list_for_each_entry_reverse(policy, &net->xfrm.policy_all, walk.all) {
 [..]
 |  1314                                            xfrm_policy_id2dir(policy->index));
 |  1315                  if (!chain) {
 |  1316                          void *p = xfrm_policy_inexact_insert(policy, dir, 0);

Fix this by updating 'dir' based on current policy.  Otherwise, the
inexact policies won't be found anymore during lookup, as they get
hashed to a bogus bin.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: cc1bb845 ("xfrm: policy: return NULL when inexact search needed")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_policy.c

@@ -1303,15 +1303,16 @@ 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 (policy->walk.dead ||
-		    xfrm_policy_id2dir(policy->index) >= XFRM_POLICY_MAX) {
+		if (policy->walk.dead)
+			continue;
+		dir = xfrm_policy_id2dir(policy->index);
+		if (dir >= XFRM_POLICY_MAX) {
 			/* skip socket policies */
 			continue;
 		}
 		newpos = NULL;
 		chain = policy_hash_bysel(net, &policy->selector,
-					  policy->family,
-					  xfrm_policy_id2dir(policy->index));
+					  policy->family, dir);
 		if (!chain) {
 			void *p = xfrm_policy_inexact_insert(policy, dir, 0);