netfilter: nf_queue: fix possible use-after-free

commit c387307024 upstream.

Eric Dumazet says:
  The sock_hold() side seems suspect, because there is no guarantee
  that sk_refcnt is not already 0.

On failure, we cannot queue the packet and need to indicate an
error.  The packet will be dropped by the caller.

v2: split skb prefetch hunk into separate change

Fixes: 271b72c7fa ("udp: RCU handling for Unicast packets.")
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/net/netfilter/nf_queue.h

@@ -32,7 +32,7 @@ void nf_register_queue_handler(struct net *net, const struct nf_queue_handler *q
 void nf_unregister_queue_handler(struct net *net);
 void nf_reinject(struct nf_queue_entry *entry, unsigned int verdict);
 
-void nf_queue_entry_get_refs(struct nf_queue_entry *entry);
+bool nf_queue_entry_get_refs(struct nf_queue_entry *entry);
 void nf_queue_entry_release_refs(struct nf_queue_entry *entry);
 
 static inline void init_hashrandom(u32 *jhash_initval)

net/netfilter/nf_queue.c

@@ -80,10 +80,13 @@ void nf_queue_entry_release_refs(struct nf_queue_entry *entry)
 EXPORT_SYMBOL_GPL(nf_queue_entry_release_refs);
 
 /* Bump dev refs so they don't vanish while packet is out */
-void nf_queue_entry_get_refs(struct nf_queue_entry *entry)
+bool nf_queue_entry_get_refs(struct nf_queue_entry *entry)
 {
 	struct nf_hook_state *state = &entry->state;
 
+	if (state->sk && !refcount_inc_not_zero(&state->sk->sk_refcnt))
+		return false;
+
 	if (state->in)
 		dev_hold(state->in);
 	if (state->out)
@@ -102,6 +105,7 @@ void nf_queue_entry_get_refs(struct nf_queue_entry *entry)
 			dev_hold(physdev);
 	}
 #endif
+	return true;
 }
 EXPORT_SYMBOL_GPL(nf_queue_entry_get_refs);
 
@@ -159,7 +163,11 @@ static int __nf_queue(struct sk_buff *skb, const struct nf_hook_state *state,
 		.size	= sizeof(*entry) + afinfo->route_key_size,
 	};
 
-	nf_queue_entry_get_refs(entry);
+	if (!nf_queue_entry_get_refs(entry)) {
+		kfree(entry);
+		return -ENOTCONN;
+	}
+
 	afinfo->saveroute(skb, entry);
 	status = qh->outfn(entry, queuenum);
 

net/netfilter/nfnetlink_queue.c

@@ -693,9 +693,15 @@ static struct nf_queue_entry *
 nf_queue_entry_dup(struct nf_queue_entry *e)
 {
 	struct nf_queue_entry *entry = kmemdup(e, e->size, GFP_ATOMIC);
-	if (entry)
-		nf_queue_entry_get_refs(entry);
-	return entry;
+
+	if (!entry)
+		return NULL;
+
+	if (nf_queue_entry_get_refs(entry))
+		return entry;
+
+	kfree(entry);
+	return NULL;
 }
 
 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)