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pkttype match mismatches on locally generated packets

PATCH In review Phil Oester 2 participants 3 messages Jul 18, 2006 – Jul 20, 2006

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Networking netfilter
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Phil Oester

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#0 lore raw

PATCH 1/1 pkttype match mismatches on locally generated packets

Locally generated broadcast and multicast packets have pkttype set to PACKET_LOOPBACK instead of PACKET_BROADCAST or PACKET_MULTICAST. This causes the pkttype match to fail to match packets of either type.

The below patch remedies this by using the daddr as a hint as to broadcast|multicast. While not pretty, this seems like the only way to solve the problem short of just noting this as a limitation of the match.

This resolves bug #484

Phil

Signed-off-by Phil Oester <[email protected]>
author
#1 lore raw
Quoted 8 lines · Phil Oester

Locally generated broadcast and multicast packets have pkttype set to PACKET_LOOPBACK instead of PACKET_BROADCAST or PACKET_MULTICAST. This causes the pkttype match to fail to match packets of either type.

The below patch remedies this by using the daddr as a hint as to broadcast|multicast. While not pretty, this seems like the only way to solve the problem short of just noting this as a limitation of the match.

Quoted 5 lines

This resolves bug #484

Phil

Signed-off-by Phil Oester <[email protected]>

And this time the patch is attached...

Phil

net/netfilter/xt_pkttype.c +11 -1
@@ -9,6 +9,8 @@
 #include <linux/skbuff.h>
 #include <linux/if_ether.h>
 #include <linux/if_packet.h>
+#include <linux/in.h>
+#include <linux/ip.h>
 
 #include <linux/netfilter/xt_pkttype.h>
 #include <linux/netfilter/x_tables.h>

@@ -28,9 +30,17 @@
       unsigned int protoff,
       int *hotdrop)
 {
+	u_int8_t type;
 	const struct xt_pkttype_info *info = matchinfo;
 
-	return (skb->pkt_type == info->pkttype) ^ info->invert;
+	if (skb->pkt_type == PACKET_LOOPBACK)
+		type = (MULTICAST(skb->nh.iph->daddr)
+			? PACKET_MULTICAST
+			: PACKET_BROADCAST);
+	else
+		type = skb->pkt_type;
+
+	return (type == info->pkttype) ^ info->invert;
 }
 
 static struct xt_match pkttype_match = {
#2 lore raw
In reply to Phil Oester
Quoted 9 lines · Phil Oester

Locally generated broadcast and multicast packets have pkttype set to PACKET_LOOPBACK instead of PACKET_BROADCAST or PACKET_MULTICAST. This causes the pkttype match to fail to match packets of either type.

The below patch remedies this by using the daddr as a hint as to broadcast|multicast. While not pretty, this seems like the only way to solve the problem short of just noting this as a limitation of the match.

This resolves bug #484

Thanks Phil. I thought about just adding PACKET_LOOPBACK support to userspace, but this way seems better, so applied.