netfilter: ipv6: avoid nf_iterate recursion

The previous patch changed nf_ct_frag6_gather() to morph reassembled skb
with the previous one.

This means that the return value is always NULL or the skb argument.
So change it to an err value.

Instead of invoking NF_HOOK recursively with threshold to skip already-called hooks
we can now just return NF_ACCEPT to move on to the next hook except for
-EINPROGRESS (which means skb has been queued for reassembly), in which case we
return NF_STOLEN.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 5 insertions, 9 deletions

diff --git a/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c b/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c
index fb96b1018884..f7aab5ab93a5 100644
--- a/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c
+++ b/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c
@@ -55,7 +55,7 @@ static unsigned int ipv6_defrag(void *priv,
 				struct sk_buff *skb,
 				const struct nf_hook_state *state)
 {
-	struct sk_buff *reasm;
+	int err;
 
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
 	/* Previously seen (loopback)?	*/
@@ -63,17 +63,13 @@ static unsigned int ipv6_defrag(void *priv,
 		return NF_ACCEPT;
 #endif
 
-	reasm = nf_ct_frag6_gather(state->net, skb,
-				   nf_ct6_defrag_user(state->hook, skb));
+	err = nf_ct_frag6_gather(state->net, skb,
+				 nf_ct6_defrag_user(state->hook, skb));
 	/* queued */
-	if (reasm == NULL)
+	if (err == -EINPROGRESS)
 		return NF_STOLEN;
 
-	NF_HOOK_THRESH(NFPROTO_IPV6, state->hook, state->net, state->sk, reasm,
-		       state->in, state->out,
-		       state->okfn, NF_IP6_PRI_CONNTRACK_DEFRAG + 1);
-
-	return NF_STOLEN;
+	return NF_ACCEPT;
 }
 
 static struct nf_hook_ops ipv6_defrag_ops[] = {