[PATCH 2/2 v2] bonding: COW before overwriting the destination MAC address

When there is a ptype handler holding a clone of this skb, whose
destination MAC addresse is overwritten, the owner of this handler may
get a corrupted packet.

Signed-off-by: Changli Gao <redacted>
---
v2: fix the bug in the previous one. Thank him.
 drivers/net/bonding/bond_main.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 912b416..7b7ca97 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c

@@ -1511,9 +1511,13 @@ static struct sk_buff *bond_handle_frame(struct sk_buff *skb)
 	if (bond_dev->priv_flags & IFF_MASTER_ALB &&
 	    bond_dev->priv_flags & IFF_BRIDGE_PORT &&
 	    skb->pkt_type == PACKET_HOST) {
-		u16 *dest = (u16 *) eth_hdr(skb)->h_dest;
 
-		memcpy(dest, bond_dev->dev_addr, ETH_ALEN);
+		if (unlikely(skb_cow_head(skb,
+					  skb->data - skb_mac_header(skb)))) {
+			kfree_skb(skb);
+			return NULL;
+		}
+		memcpy(eth_hdr(skb)->h_dest, bond_dev->dev_addr, ETH_ALEN);
 	}
 
 	return skb;

Le jeudi 03 mars 2011 à 15:07 +0800, Changli Gao a écrit :

Thats minor, but using :

u16 *dest = eth_hdr(skb)->h_dest;

memcpy(dest, ptr, ETH_ALEN);

Is better because compiler knows both destination and source are at
least aligned on shorts.

On some arches, it helps to not using 6 bytes copy, but 3 shorts.

On Thu, Mar 3, 2011 at 3:55 PM, Eric Dumazet [off-list ref] wrote:

Thats minor, but using :

u16 *dest = eth_hdr(skb)->h_dest;

memcpy(dest, ptr, ETH_ALEN);

Is better because compiler knows both destination and source are at
least aligned on shorts.

On some arches, it helps to not using 6 bytes copy, but 3 shorts.

Is it still true if ptr isn't aligned on shorts? And
net_device.dev_addr is an unsigned char *pointer. Thanks.

-- 
Regards,
Changli Gao(xiaosuo@gmail.com)

Le jeudi 03 mars 2011 à 16:21 +0800, Changli Gao a écrit :

On Thu, Mar 3, 2011 at 3:55 PM, Eric Dumazet [off-list ref] wrote:

quoted

Thats minor, but using :

u16 *dest = eth_hdr(skb)->h_dest;

memcpy(dest, ptr, ETH_ALEN);

Is better because compiler knows both destination and source are at
least aligned on shorts.

On some arches, it helps to not using 6 bytes copy, but 3 shorts.

Is it still true if ptr isn't aligned on shorts? And
net_device.dev_addr is an unsigned char *pointer. Thanks.

dev_addr[] was aligned to word boundaries (because of natural structure
alignment), but the recent changes made it a char *pointer, so gcc is
not able to make this true anymore.

This could change if dev_addr was a pointer to struct netdev_hw_addr

From: Changli Gao <redacted>
Date: Thu,  3 Mar 2011 15:07:14 +0800

When there is a ptype handler holding a clone of this skb, whose
destination MAC addresse is overwritten, the owner of this handler may
get a corrupted packet.

Signed-off-by: Changli Gao <redacted>

Applied.