[NETFILTER]: Don't use skb_header_pointer in amanda conntrack helper

Fixes broken packets, noticed by Matthias Andree <matthias.andree@gmx.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/netfilter/ip_conntrack_amanda.c

@@ -49,7 +49,7 @@ static int help(struct sk_buff *skb,
 {
 	struct ip_conntrack_expect *exp;
 	struct ip_ct_amanda_expect *exp_amanda_info;
-	char *amp, *data, *data_limit, *tmp;
+	char *data, *data_limit, *tmp;
 	unsigned int dataoff, i;
 	u_int16_t port, len;
 
@@ -70,11 +70,9 @@ static int help(struct sk_buff *skb,
 	}
 
 	LOCK_BH(&amanda_buffer_lock);
-	amp = skb_header_pointer(skb, dataoff,
-				 skb->len - dataoff, amanda_buffer);
-	BUG_ON(amp == NULL);
-	data = amp;
-	data_limit = amp + skb->len - dataoff;
+	skb_copy_bits(skb, dataoff, amanda_buffer, skb->len - dataoff);
+	data = amanda_buffer;
+	data_limit = amanda_buffer + skb->len - dataoff;
 	*data_limit = '\0';
 
 	/* Search for the CONNECT string */
@@ -110,7 +108,7 @@ static int help(struct sk_buff *skb,
 		exp->mask.dst.u.tcp.port = 0xFFFF;
 
 		exp_amanda_info = &exp->help.exp_amanda_info;
-		exp_amanda_info->offset = tmp - amp;
+		exp_amanda_info->offset = tmp - amanda_buffer;
 		exp_amanda_info->port   = port;
 		exp_amanda_info->len    = len;