[ 24/79] macvtap: correctly linearize skb when zerocopy is used

From: Greg Kroah-Hartman
Date: Fri Jul 26 2013 - 17:36:14 EST

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


From: Jason Wang <jasowang@xxxxxxxxxx>

[ Upstream commit 61d46bf979d5cd7c164709a80ad5676a35494aae ]

Userspace may produce vectors greater than MAX_SKB_FRAGS. When we try to
linearize parts of the skb to let the rest of iov to be fit in
the frags, we need count copylen into linear when calling macvtap_alloc_skb()
instead of partly counting it into data_len. Since this breaks
zerocopy_sg_from_iovec() since its inner counter assumes nr_frags should
be zero at beginning. This cause nr_frags to be increased wrongly without
setting the correct frags.

This bug were introduced from b92946e2919134ebe2a4083e4302236295ea2a73
(macvtap: zerocopy: validate vectors before building skb).

Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
drivers/net/macvtap.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -647,6 +647,7 @@ static ssize_t macvtap_get_user(struct m
int vnet_hdr_len = 0;
int copylen = 0;
bool zerocopy = false;
+ size_t linear;

if (q->flags & IFF_VNET_HDR) {
vnet_hdr_len = q->vnet_hdr_sz;
@@ -701,11 +702,14 @@ static ssize_t macvtap_get_user(struct m
copylen = vnet_hdr.hdr_len;
if (!copylen)
copylen = GOODCOPY_LEN;
- } else
+ linear = copylen;
+ } else {
copylen = len;
+ linear = vnet_hdr.hdr_len;
+ }

skb = macvtap_alloc_skb(&q->sk, NET_IP_ALIGN, copylen,
- vnet_hdr.hdr_len, noblock, &err);
+ linear, noblock, &err);
if (!skb)
goto err;

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