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Subject[PATCH 63/75] tuntap: correctly linearize skb when zerocopy is used
Date
3.8.13.6 -stable review patch.  If anyone has any objections, please let me know.

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

From: Jason Wang <jasowang@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 <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
drivers/net/tun.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 2a56317..0ebfa18 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1045,7 +1045,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
{
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;
@@ -1109,10 +1109,13 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
copylen = gso.hdr_len;
if (!copylen)
copylen = GOODCOPY_LEN;
- } else
+ linear = copylen;
+ } else {
copylen = len;
+ linear = gso.hdr_len;
+ }

- skb = tun_alloc_skb(tfile, align, copylen, gso.hdr_len, noblock);
+ skb = tun_alloc_skb(tfile, align, copylen, linear, noblock);
if (IS_ERR(skb)) {
if (PTR_ERR(skb) != -EAGAIN)
tun->dev->stats.rx_dropped++;
--
1.8.1.2


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