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

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Date:	Thu,  3 Mar 2011 15:07:14 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Jay Vosburgh <fubar@...ibm.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	Changli Gao <xiaosuo@...il.com>
Subject: [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 <xiaosuo@...il.com>
---
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;
--
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