linux-kernel - [PATCH 3.16.y-ckt 074/126] xen-netfront: use correct linear area after linearizing an skb

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Date:	Tue, 27 Jan 2015 12:16:19 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	David Vrabel <david.vrabel@...rix.com>,
	"David S. Miller" <davem@...emloft.net>,
	Stefan Bader <stefan.bader@...onical.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 074/126] xen-netfront: use correct linear area after linearizing an skb

3.16.7-ckt5 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Vrabel <david.vrabel@...rix.com>

commit 11d3d2a16cc1f05c6ece69a4392e99efb85666a6 upstream.

Commit 97a6d1bb2b658ac85ed88205ccd1ab809899884d (xen-netfront: Fix
handling packets on compound pages with skb_linearize) attempted to
fix a problem where an skb that would have required too many slots
would be dropped causing TCP connections to stall.

However, it filled in the first slot using the original buffer and not
the new one and would use the wrong offset and grant access to the
wrong page.

Netback would notice the malformed request and stop all traffic on the
VIF, reporting:

    vif vif-3-0 vif3.0: txreq.offset: 85e, size: 4002, end: 6144
    vif vif-3-0 vif3.0: fatal error; disabling device

Reported-by: Anthony Wright <anthony@...rnetdata.com>
Tested-by: Anthony Wright <anthony@...rnetdata.com>
Signed-off-by: David Vrabel <david.vrabel@...rix.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Cc: Stefan Bader <stefan.bader@...onical.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/net/xen-netfront.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 3e0019503440..fc49005ddb5d 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -627,6 +627,9 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 				    slots, skb->len);
 		if (skb_linearize(skb))
 			goto drop;
+		data = skb->data;
+		offset = offset_in_page(data);
+		len = skb_headlen(skb);
 	}
 
 	spin_lock_irqsave(&queue->tx_lock, flags);
-- 
2.1.4

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