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SubjectRe: [PATCH v2 net 1/2] tuntap: correctly linearize skb when zerocopy is used
On Wed, Jul 10, 2013 at 01:43:27PM +0800, Jason Wang wrote:
> 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>

> ---
> - This patch is needed for stable.
> - Changes from v1: introduce a local variable to track linear size
> ---
> drivers/net/tun.c | 9 ++++++---
> 1 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 9c61f87..c3cb60b 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1044,7 +1044,7 @@ 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;
> @@ -1108,10 +1108,13 @@ 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++;
> --
> 1.7.1


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