[048/251] tuntap: correctly linearize skb when zerocopy is used

[Steven Rostedt]

3.6.11.9-rc1 stable review patch.
If anyone has any objections, please let me know.

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

From: Jason Wang <jasowang@xxxxxxxxxx>

[ Upstream commit 3dd5c3308e8b671e8e8882ba972f51cefbe9fd0d ]

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 tun_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 0690899b4d4501b3505be069b9a687e68ccbe15b
(tun: experimental zero copy tx support)

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: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 drivers/net/tun.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index ef7710f..ad08dee 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -692,7 +692,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, void *msg_control,
 {
 	struct tun_pi pi = { 0, cpu_to_be16(ETH_P_IP) };
 	struct sk_buff *skb;
-	size_t len = total_len, align = NET_SKB_PAD;
+	size_t len = total_len, align = NET_SKB_PAD, linear;
 	struct virtio_net_hdr gso = { 0 };
 	int offset = 0;
 	int copylen;
@@ -755,10 +755,14 @@ static ssize_t tun_get_user(struct tun_struct *tun, void *msg_control,
 			copylen = gso.hdr_len;
 		if (!copylen)
 			copylen = GOODCOPY_LEN;
-	} else
+		linear = copylen;
+	} else {
 		copylen = len;
+		linear = gso.hdr_len;
+	}
 
 	skb = tun_alloc_skb(tun, align, copylen, gso.hdr_len, noblock);
+	skb = tun_alloc_skb(tun, align, copylen, linear, noblock);
 	if (IS_ERR(skb)) {
 		if (PTR_ERR(skb) != -EAGAIN)
 			tun->dev->stats.rx_dropped++;
-- 
1.7.10.4


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