xfrm: policy: fix infinite loop when merging src-nodes

With very small change to test script we can trigger softlockup due to
bogus assignment of 'p' (policy to be examined) on restart.

Previously the two to-be-merged nodes had same address/prefixlength pair,
so no erase/reinsert was necessary, we only had to append the list from
node a to b.

If prefix lengths are different, the node has to be deleted and re-inserted
into the tree, with the updated prefix length.  This was broken; due to
bogus update to 'p' this loops forever.

Add a 'restart' label and use that instead.

While at it, don't perform the unneeded reinserts of the policies that
are already sorted into the 'new' node.

A previous patch in this series made xfrm_policy_inexact_list_reinsert()
use the relative position indicator to sort policies according to age in
case priorities are identical.

Fixes: 6ac098b ("xfrm: policy: add 2nd-level saddr trees for inexact policies")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_policy.c

@@ -886,12 +886,13 @@ static void xfrm_policy_inexact_node_reinsert(struct net *net,
 					      struct rb_root *new,
 					      u16 family)
 {
-	struct rb_node **p, *parent = NULL;
 	struct xfrm_pol_inexact_node *node;
+	struct rb_node **p, *parent;
 
 	/* we should not have another subtree here */
 	WARN_ON_ONCE(!RB_EMPTY_ROOT(&n->root));
-
+restart:
+	parent = NULL;
 	p = &new->rb_node;
 	while (*p) {
 		u8 prefixlen;
@@ -911,12 +912,11 @@ static void xfrm_policy_inexact_node_reinsert(struct net *net,
 		} else {
 			struct xfrm_policy *tmp;
 
-			hlist_for_each_entry(tmp, &node->hhead, bydst)
-				tmp->bydst_reinsert = true;
-			hlist_for_each_entry(tmp, &n->hhead, bydst)
+			hlist_for_each_entry(tmp, &n->hhead, bydst) {
 				tmp->bydst_reinsert = true;
+				hlist_del_rcu(&tmp->bydst);
+			}
 
-			INIT_HLIST_HEAD(&node->hhead);
 			xfrm_policy_inexact_list_reinsert(net, node, family);
 
 			if (node->prefixlen == n->prefixlen) {
@@ -928,8 +928,7 @@ static void xfrm_policy_inexact_node_reinsert(struct net *net,
 			kfree_rcu(n, rcu);
 			n = node;
 			n->prefixlen = prefixlen;
-			*p = new->rb_node;
-			parent = NULL;
+			goto restart;
 		}
 	}
 

tools/testing/selftests/net/xfrm_policy.sh

@@ -78,8 +78,8 @@ do_overlap()
     # adds a new node in the 10.0.0.0/24 tree (dst node exists).
     ip -net $ns xfrm policy add src 10.2.0.0/24 dst 10.0.0.0/24 dir fwd priority 200 action block
 
-    # adds a 10.2.0.0/24 node, but for different dst.
-    ip -net $ns xfrm policy add src 10.2.0.0/24 dst 10.0.1.0/24 dir fwd priority 200 action block
+    # adds a 10.2.0.0/23 node, but for different dst.
+    ip -net $ns xfrm policy add src 10.2.0.0/23 dst 10.0.1.0/24 dir fwd priority 200 action block
 
     # dst now overlaps with the 10.0.1.0/24 ESP policy in fwd.
     # kernel must 'promote' existing one (10.0.0.0/24) to 10.0.0.0/23.