[PATCH] netpoll: make arp replies through netpoll use mac address of sender

[PATCH] netpoll: make arp replies through netpoll use mac address of sender

[Neil Horman]

Back in 2.4 arp requests that were recevied by netpoll were processed in
netconsole_receive_skb, where they were responded to using the src mac of the
request sender.  In the 2.6 kernel arp_reply is responsible for this function,
but instead of using the src mac address of the incomming request, the stored
mac address that was registered for the netconsole application is used.  While
this is usually ok, it can lead to failures in netpoll in some situations
(specifically situations where a network may have two gateways, as arp requests
from one may be responded to using the mac address of the other).  This patch
reverts the behavior to what we had in 2.4, in which all arp requests are sent
back using the src address of the request sender.

Thanks & Regards
Neil

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>


 netpoll.c |   14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)


diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 3c58846..5833b21 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -331,6 +331,7 @@ static void arp_reply(struct sk_buff *sk
 	unsigned char *arp_ptr;
 	int size, type = ARPOP_REPLY, ptype = ETH_P_ARP;
 	__be32 sip, tip;
+	unsigned char *sha;
 	struct sk_buff *send_skb;
 	struct netpoll *np = NULL;
 
@@ -357,9 +358,14 @@ static void arp_reply(struct sk_buff *sk
 	    arp->ar_op != htons(ARPOP_REQUEST))
 		return;
 
-	arp_ptr = (unsigned char *)(arp+1) + skb->dev->addr_len;
+	arp_ptr = (unsigned char *)(arp+1);
+	/* save the location of the src hw addr */
+	sha = arp_ptr;
+	arp_ptr += skb->dev->addr_len;
 	memcpy(&sip, arp_ptr, 4);
-	arp_ptr += 4 + skb->dev->addr_len;
+	arp_ptr += 4;
+	/* if we actually cared about dst hw addr, it would get copied here */
+	arp_ptr += skb->dev->addr_len;
 	memcpy(&tip, arp_ptr, 4);
 
 	/* Should we ignore arp? */
@@ -382,7 +388,7 @@ static void arp_reply(struct sk_buff *sk
 
 	if (np->dev->hard_header &&
 	    np->dev->hard_header(send_skb, skb->dev, ptype,
-				 np->remote_mac, np->local_mac,
+				 sha, np->local_mac,
 				 send_skb->len) < 0) {
 		kfree_skb(send_skb);
 		return;
@@ -406,7 +412,7 @@ static void arp_reply(struct sk_buff *sk
 	arp_ptr += np->dev->addr_len;
 	memcpy(arp_ptr, &tip, 4);
 	arp_ptr += 4;
-	memcpy(arp_ptr, np->remote_mac, np->dev->addr_len);
+	memcpy(arp_ptr, sha, np->dev->addr_len);
 	arp_ptr += np->dev->addr_len;
 	memcpy(arp_ptr, &sip, 4);
 
-- 
/***************************************************
 *Neil Horman
 *Software Engineer
 *gpg keyid: 1024D / 0x92A74FA1 - http://pgp.mit.edu
 ***************************************************/

Re: [PATCH] netpoll: make arp replies through netpoll use mac address of sender

[Chris Lalancette]

Neil Horman wrote:
> Back in 2.4 arp requests that were recevied by netpoll were processed in
> netconsole_receive_skb, where they were responded to using the src mac of the
> request sender.  In the 2.6 kernel arp_reply is responsible for this function,
> but instead of using the src mac address of the incomming request, the stored
> mac address that was registered for the netconsole application is used.  While
> this is usually ok, it can lead to failures in netpoll in some situations
> (specifically situations where a network may have two gateways, as arp requests
> from one may be responded to using the mac address of the other).  This patch
> reverts the behavior to what we had in 2.4, in which all arp requests are sent
> back using the src address of the request sender.
> 
> Thanks & Regards
> Neil
> 
> Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> 

Neil and I worked on this together, adding my ACK

Acked-by: Chris Lalancette <clalance@redhat.com>

Re: [PATCH] netpoll: make arp replies through netpoll use mac address of sender

[David Miller]

From: Neil Horman <nhorman@tuxdriver.com>
Date: Thu, 7 Dec 2006 14:45:53 -0500

> Back in 2.4 arp requests that were recevied by netpoll were processed in
> netconsole_receive_skb, where they were responded to using the src mac of the
> request sender.  In the 2.6 kernel arp_reply is responsible for this function,
> but instead of using the src mac address of the incomming request, the stored
> mac address that was registered for the netconsole application is used.  While
> this is usually ok, it can lead to failures in netpoll in some situations
> (specifically situations where a network may have two gateways, as arp requests
> from one may be responded to using the mac address of the other).  This patch
> reverts the behavior to what we had in 2.4, in which all arp requests are sent
> back using the src address of the request sender.
> 
> Signed-off-by: Neil Horman <nhorman@tuxdriver.com>

Applied, and I'll push this to -stable, thanks Neil.

But please submit networking patches next time to
netdev@vger.kernel.org, most of the networking developers did not see
this patch because you sent it to the user help list (linux-net)
instead of the developer list (netdev).

Thanks again.

Re: [PATCH] netpoll: make arp replies through netpoll use mac address of sender

[Neil Horman]

On Fri, Dec 08, 2006 at 12:07:27AM -0800, David Miller wrote:
> From: Neil Horman <nhorman@tuxdriver.com>
> Date: Thu, 7 Dec 2006 14:45:53 -0500
> 
> > Back in 2.4 arp requests that were recevied by netpoll were processed in
> > netconsole_receive_skb, where they were responded to using the src mac of the
> > request sender.  In the 2.6 kernel arp_reply is responsible for this function,
> > but instead of using the src mac address of the incomming request, the stored
> > mac address that was registered for the netconsole application is used.  While
> > this is usually ok, it can lead to failures in netpoll in some situations
> > (specifically situations where a network may have two gateways, as arp requests
> > from one may be responded to using the mac address of the other).  This patch
> > reverts the behavior to what we had in 2.4, in which all arp requests are sent
> > back using the src address of the request sender.
> > 
> > Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> 
> Applied, and I'll push this to -stable, thanks Neil.
> 
> But please submit networking patches next time to
> netdev@vger.kernel.org, most of the networking developers did not see
> this patch because you sent it to the user help list (linux-net)
> instead of the developer list (netdev).
> 
My bad, wasn't thinking.  Thanks guys!
Neil

> Thanks again.

-- 
/***************************************************
 *Neil Horman
 *Software Engineer
 *gpg keyid: 1024D / 0x92A74FA1 - http://pgp.mit.edu
 ***************************************************/