[PATCH 3.14 05/34] xen-netfront: Remove BUGs on paged skb data which crosses a page boundary

From: Greg Kroah-Hartman
Date: Sun Dec 14 2014 - 15:37:38 EST

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


From: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>

commit 8d609725d4357f499e2103e46011308b32f53513 upstream.

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")
Signed-off-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
Reviewed-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/net/xen-netfront.c | 5 -----
1 file changed, 5 deletions(-)

--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -469,9 +469,6 @@ static void xennet_make_frags(struct sk_
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_
while (len > 0) {
unsigned long bytes;

- BUG_ON(offset >= PAGE_SIZE);
bytes = PAGE_SIZE - offset;
if (bytes > len)
bytes = len;

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