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

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

From: Jason Wang <jasow...@redhat.com>

[ 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 <m...@redhat.com>
Signed-off-by: Jason Wang <jasow...@redhat.com>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Steven Rostedt <rost...@goodmis.org>
---
 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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