[PATCH net 2/2] macvtap: correctly linearize skb when zerocopy is used

[Jason Wang <jasowang@redhat.com>]

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@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
This patch is needed for stable.
---
 drivers/net/macvtap.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index f2c4a3b..b213020 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -770,7 +770,8 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
 		copylen = len;
 
 	skb = macvtap_alloc_skb(&q->sk, NET_IP_ALIGN, copylen,
-				vnet_hdr.hdr_len, noblock, &err);
+				zerocopy ? copylen : vnet_hdr.hdr_len,
+				noblock, &err);
 	if (!skb)
 		goto err;
 
-- 
1.7.1