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    Subject[ 23/79] tuntap: correctly linearize skb when zerocopy is used
    Date
    3.10-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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/tun.c | 9 ++++++---
    1 file changed, 6 insertions(+), 3 deletions(-)

    --- a/drivers/net/tun.c
    +++ b/drivers/net/tun.c
    @@ -1044,7 +1044,7 @@ static ssize_t tun_get_user(struct tun_s
    {
    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;
    @@ -1108,10 +1108,13 @@ static ssize_t tun_get_user(struct tun_s
    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++;



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