netfilter: nfnetlink_hook: fix check for snprintf() overflow

The kernel version of snprintf() can't return negatives.  The
"ret > (int)sizeof(sym)" check is off by one because and it should be
>=.  Finally, we need to set a negative error code.

Fixes: e2cf17d3 ("netfilter: add new hook nfnl subsystem")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nfnetlink_hook.c

@@ -126,8 +126,10 @@ static int nfnl_hook_dump_one(struct sk_buff *nlskb,
 
 #ifdef CONFIG_KALLSYMS
 	ret = snprintf(sym, sizeof(sym), "%ps", ops->hook);
-	if (ret < 0 || ret > (int)sizeof(sym))
+	if (ret >= sizeof(sym)) {
+		ret = -EINVAL;
 		goto nla_put_failure;
+	}
 
 	module_name = strstr(sym, " [");
 	if (module_name) {