[PATCH][trusty/utopic SRU] xen-netfront: Remove BUGs on paged skb data which crosses a page boundary

[Seth Forshee]

These BUGs can be erroneously triggered by frags which refer to
tail pages within a compound page. The data in these pages may
overrun the hardware page while still being contained within the
compound page, but since compound_order() evaluates to 0 for tail
pages the assertion fails. The code already iterates through
subsequent pages correctly in this scenario, so the BUGs are
unnecessary and can be removed.

Fixes: f36c374782e4 ("xen/netfront: handle compound page fragments on transmit")
Cc: <stable at vger.kernel.org> # 3.7+
Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
Reviewed-by: David Vrabel <david.vrabel at citrix.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 8d609725d4357f499e2103e46011308b32f53513)
BugLink: http://bugs.launchpad.net/bugs/1275879
---
 drivers/net/xen-netfront.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index fff9bbe..69e0cd6 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -469,9 +469,6 @@ static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
 		len = skb_frag_size(frag);
 		offset = frag->page_offset;
 
-		/* Data must not cross a page boundary. */
-		BUG_ON(len + offset > PAGE_SIZE<<compound_order(page));
-
 		/* Skip unused frames from start of page */
 		page += offset >> PAGE_SHIFT;
 		offset &= ~PAGE_MASK;
@@ -479,8 +476,6 @@ static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
 		while (len > 0) {
 			unsigned long bytes;
 
-			BUG_ON(offset >= PAGE_SIZE);
-
 			bytes = PAGE_SIZE - offset;
 			if (bytes > len)
 				bytes = len;
-- 
1.9.1