[PATCH] netfilter: fix looped (broad|multi)cast's bogus MACs in NFQUEUE

[PATCH] netfilter: fix looped (broad|multi)cast's bogus MACs in NFQUEUE

[Nicolas Cavallari]

By default, when broadcast or multicast packet are sent from a local
application, they are sent to the interface then looped by the kernel
to other local applications, going throught netfilter hooks in the process.

These looped packet have their MAC header removed from the skb by the kernel
looping code.
This confuse netfilter's netlink queue because it tries to extract a hardware
address from these packets, but extracts a part of the IP header instead.

This patch prevent NFQUEUE to include a MAC header in the netlink message
if there is none.

Signed-off-by: Nicolas Cavallari <cavallar@lri.fr>
---
To reproduce the bug, run libnetfilter_queue's nfqnl_test.c and add
some iptables -j NFQUEUE rule in PREROUTING.
Then, either ping -b 255.255.255.255 or ping nonexistenthost.local (if
avahi or another multicast dns client is configured)

If you see MAC addresses like 40:00:ff:11:0d::70 (for mdns) or
 00:00:80:11:70:62 then you can see that they match this part of the packet's
ip header :

               |flags| fragment offset|
 |ttl| protocol|       checksum       |

patch done against 2.6.39.1 but should also apply to nf-next
---
--- linux-2.6.39.1/net/netfilter/nfnetlink_queue.c	2011-06-08 14:43:41.188003302 +0200
+++ linux-2.6.39.1/net/netfilter/nfnetlink_queue.c	2011-06-08 14:46:10.892003541 +0200
@@ -335,7 +335,8 @@ nfqnl_build_packet_message(struct nfqnl_
 	if (entskb->mark)
 		NLA_PUT_BE32(skb, NFQA_MARK, htonl(entskb->mark));
 
-	if (indev && entskb->dev) {
+	if (indev && entskb->dev &&
+	    entskb->network_header != entskb->mac_header) {
 		struct nfqnl_msg_packet_hw phw;
 		int len = dev_parse_header(entskb, phw.hw_addr);
 		if (len) {

Re: [PATCH] netfilter: fix looped (broad|multi)cast's bogus MACs in NFQUEUE

[Florian Westphal]

Nicolas Cavallari <Nicolas.Cavallari@lri.fr> wrote:
> By default, when broadcast or multicast packet are sent from a local
> application, they are sent to the interface then looped by the kernel
> to other local applications, going throught netfilter hooks in the process.
> 
> These looped packet have their MAC header removed from the skb by the kernel
> looping code.
> This confuse netfilter's netlink queue because it tries to extract a hardware
> address from these packets, but extracts a part of the IP header instead.

[..]

> patch done against 2.6.39.1 but should also apply to nf-next
> ---
> --- linux-2.6.39.1/net/netfilter/nfnetlink_queue.c	2011-06-08 14:43:41.188003302 +0200
> +++ linux-2.6.39.1/net/netfilter/nfnetlink_queue.c	2011-06-08 14:46:10.892003541 +0200
> @@ -335,7 +335,8 @@ nfqnl_build_packet_message(struct nfqnl_
>  	if (entskb->mark)
>  		NLA_PUT_BE32(skb, NFQA_MARK, htonl(entskb->mark));
>  
> -	if (indev && entskb->dev) {
> +	if (indev && entskb->dev &&
> +	    entskb->network_header != entskb->mac_header) {

nfnetlink_log has the same problem.

Re: [PATCH] netfilter: fix looped (broad|multi)cast's bogus MACs in NFQUEUE

[Nicolas Cavallari]

> nfnetlink_log has the same problem.

I also figured from source that ip_queue has the same problem too, so
the next patch fixes that too.

[PATCH] netfilter: fix looped (broad|multi)cast's MAC handling.

[Nicolas Cavallari]

By default, when broadcast or multicast packet are sent from a local
application, they are sent to the interface then looped by the kernel
to other local applications, going throught netfilter hooks in the process.

These looped packet have their MAC header removed from the skb by the kernel
looping code.
This confuse various netfilter's netlink queue, netlink log and the
legacy ip_queue, because they try to extract a hardware
address from these packets, but extracts a part of the IP header instead.

This patch prevent NFQUEUE, NFLOG and ip_QUEUE to include a MAC header
if there is none in the packet.
---
 net/ipv4/netfilter/ip_queue.c   |    3 ++-
 net/ipv6/netfilter/ip6_queue.c  |    3 ++-
 net/netfilter/nfnetlink_log.c   |    3 ++-
 net/netfilter/nfnetlink_queue.c |    3 ++-
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/netfilter/ip_queue.c b/net/ipv4/netfilter/ip_queue.c
index f7f9bd7..5c9b9d9 100644
--- a/net/ipv4/netfilter/ip_queue.c
+++ b/net/ipv4/netfilter/ip_queue.c
@@ -203,7 +203,8 @@ ipq_build_packet_message(struct nf_queue_entry *entry, int *errp)
 	else
 		pmsg->outdev_name[0] = '\0';
 
-	if (entry->indev && entry->skb->dev) {
+	if (entry->indev && entry->skb->dev &&
+	    entry->skb->mac_header != entry->skb->network_header) {
 		pmsg->hw_type = entry->skb->dev->type;
 		pmsg->hw_addrlen = dev_parse_header(entry->skb,
 						    pmsg->hw_addr);
diff --git a/net/ipv6/netfilter/ip6_queue.c b/net/ipv6/netfilter/ip6_queue.c
index 065fe40..2493948 100644
--- a/net/ipv6/netfilter/ip6_queue.c
+++ b/net/ipv6/netfilter/ip6_queue.c
@@ -204,7 +204,8 @@ ipq_build_packet_message(struct nf_queue_entry *entry, int *errp)
 	else
 		pmsg->outdev_name[0] = '\0';
 
-	if (entry->indev && entry->skb->dev) {
+	if (entry->indev && entry->skb->dev &&
+	    entry->skb->mac_header != entry->skb->network_header) {
 		pmsg->hw_type = entry->skb->dev->type;
 		pmsg->hw_addrlen = dev_parse_header(entry->skb, pmsg->hw_addr);
 	}
diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
index e0ee010..2e7ccbb 100644
--- a/net/netfilter/nfnetlink_log.c
+++ b/net/netfilter/nfnetlink_log.c
@@ -456,7 +456,8 @@ __build_packet_message(struct nfulnl_instance *inst,
 	if (skb->mark)
 		NLA_PUT_BE32(inst->skb, NFULA_MARK, htonl(skb->mark));
 
-	if (indev && skb->dev) {
+	if (indev && skb->dev &&
+	    skb->mac_header != skb->network_header) {
 		struct nfulnl_msg_packet_hw phw;
 		int len = dev_parse_header(skb, phw.hw_addr);
 		if (len > 0) {
diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
index b83123f..fdd2faf 100644
--- a/net/netfilter/nfnetlink_queue.c
+++ b/net/netfilter/nfnetlink_queue.c
@@ -335,7 +335,8 @@ nfqnl_build_packet_message(struct nfqnl_instance *queue,
 	if (entskb->mark)
 		NLA_PUT_BE32(skb, NFQA_MARK, htonl(entskb->mark));
 
-	if (indev && entskb->dev) {
+	if (indev && entskb->dev &&
+	    entskb->mac_header != entskb->network_header) {
 		struct nfqnl_msg_packet_hw phw;
 		int len = dev_parse_header(entskb, phw.hw_addr);
 		if (len) {
-- 
1.7.5.3

Re: [PATCH] netfilter: fix looped (broad|multi)cast's MAC handling.

[Patrick McHardy]

On 09.06.2011 15:39, Nicolas Cavallari wrote:
> By default, when broadcast or multicast packet are sent from a local
> application, they are sent to the interface then looped by the kernel
> to other local applications, going throught netfilter hooks in the process.
> 
> These looped packet have their MAC header removed from the skb by the kernel
> looping code.
> This confuse various netfilter's netlink queue, netlink log and the
> legacy ip_queue, because they try to extract a hardware
> address from these packets, but extracts a part of the IP header instead.
> 
> This patch prevent NFQUEUE, NFLOG and ip_QUEUE to include a MAC header
> if there is none in the packet.

Please add a Signed-off-by: line to your patch so I can apply it.
Thanks!

[PATCH] netfilter: fix looped (broad|multi)cast's MAC handling.

[Nicolas Cavallari]

By default, when broadcast or multicast packet are sent from a local
application, they are sent to the interface then looped by the kernel
to other local applications, going throught netfilter hooks in the process.

These looped packet have their MAC header removed from the skb by the kernel
looping code.
This confuse various netfilter's netlink queue, netlink log and the
legacy ip_queue, because they try to extract a hardware
address from these packets, but extracts a part of the IP header instead.

This patch prevent NFQUEUE, NFLOG and ip_QUEUE to include a MAC header
if there is none in the packet.

Signed-off-by: Nicolas Cavallari <cavallar@lri.fr>
---
 net/ipv4/netfilter/ip_queue.c   |    3 ++-
 net/ipv6/netfilter/ip6_queue.c  |    3 ++-
 net/netfilter/nfnetlink_log.c   |    3 ++-
 net/netfilter/nfnetlink_queue.c |    3 ++-
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/netfilter/ip_queue.c b/net/ipv4/netfilter/ip_queue.c
index f7f9bd7..5c9b9d9 100644
--- a/net/ipv4/netfilter/ip_queue.c
+++ b/net/ipv4/netfilter/ip_queue.c
@@ -203,7 +203,8 @@ ipq_build_packet_message(struct nf_queue_entry *entry, int *errp)
 	else
 		pmsg->outdev_name[0] = '\0';
 
-	if (entry->indev && entry->skb->dev) {
+	if (entry->indev && entry->skb->dev &&
+	    entry->skb->mac_header != entry->skb->network_header) {
 		pmsg->hw_type = entry->skb->dev->type;
 		pmsg->hw_addrlen = dev_parse_header(entry->skb,
 						    pmsg->hw_addr);
diff --git a/net/ipv6/netfilter/ip6_queue.c b/net/ipv6/netfilter/ip6_queue.c
index 065fe40..2493948 100644
--- a/net/ipv6/netfilter/ip6_queue.c
+++ b/net/ipv6/netfilter/ip6_queue.c
@@ -204,7 +204,8 @@ ipq_build_packet_message(struct nf_queue_entry *entry, int *errp)
 	else
 		pmsg->outdev_name[0] = '\0';
 
-	if (entry->indev && entry->skb->dev) {
+	if (entry->indev && entry->skb->dev &&
+	    entry->skb->mac_header != entry->skb->network_header) {
 		pmsg->hw_type = entry->skb->dev->type;
 		pmsg->hw_addrlen = dev_parse_header(entry->skb, pmsg->hw_addr);
 	}
diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
index e0ee010..2e7ccbb 100644
--- a/net/netfilter/nfnetlink_log.c
+++ b/net/netfilter/nfnetlink_log.c
@@ -456,7 +456,8 @@ __build_packet_message(struct nfulnl_instance *inst,
 	if (skb->mark)
 		NLA_PUT_BE32(inst->skb, NFULA_MARK, htonl(skb->mark));
 
-	if (indev && skb->dev) {
+	if (indev && skb->dev &&
+	    skb->mac_header != skb->network_header) {
 		struct nfulnl_msg_packet_hw phw;
 		int len = dev_parse_header(skb, phw.hw_addr);
 		if (len > 0) {
diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
index b83123f..fdd2faf 100644
--- a/net/netfilter/nfnetlink_queue.c
+++ b/net/netfilter/nfnetlink_queue.c
@@ -335,7 +335,8 @@ nfqnl_build_packet_message(struct nfqnl_instance *queue,
 	if (entskb->mark)
 		NLA_PUT_BE32(skb, NFQA_MARK, htonl(entskb->mark));
 
-	if (indev && entskb->dev) {
+	if (indev && entskb->dev &&
+	    entskb->mac_header != entskb->network_header) {
 		struct nfqnl_msg_packet_hw phw;
 		int len = dev_parse_header(entskb, phw.hw_addr);
 		if (len) {
-- 
1.7.5.3

Re: [PATCH] netfilter: fix looped (broad|multi)cast's MAC handling.

[Patrick McHardy]

On 10.06.2011 09:20, Nicolas Cavallari wrote:
> By default, when broadcast or multicast packet are sent from a local
> application, they are sent to the interface then looped by the kernel
> to other local applications, going throught netfilter hooks in the process.
> 
> These looped packet have their MAC header removed from the skb by the kernel
> looping code.
> This confuse various netfilter's netlink queue, netlink log and the
> legacy ip_queue, because they try to extract a hardware
> address from these packets, but extracts a part of the IP header instead.
> 
> This patch prevent NFQUEUE, NFLOG and ip_QUEUE to include a MAC header
> if there is none in the packet.

Applied, thanks Nicolas.