• Alexis Bauvin's avatar
    tun: mark small packets as owned by the tap sock · 4b663366
    Alexis Bauvin authored
    - v1 -> v2: Move skb_set_owner_w to __tun_build_skb to reduce patch size
    
    Small packets going out of a tap device go through an optimized code
    path that uses build_skb() rather than sock_alloc_send_pskb(). The
    latter calls skb_set_owner_w(), but the small packet code path does not.
    
    The net effect is that small packets are not owned by the userland
    application's socket (e.g. QEMU), while large packets are.
    This can be seen with a TCP session, where packets are not owned when
    the window size is small enough (around PAGE_SIZE), while they are once
    the window grows (note that this requires the host to support virtio
    tso for the guest to offload segmentation).
    All this leads to inconsistent behaviour in the kernel, especially on
    netfilter modules that uses sk->socket (e.g. xt_owner).
    
    Fixes: 66ccbc9c
    
     ("tap: use build_skb() for small packet")
    Signed-off-by: default avatarAlexis Bauvin <abauvin@scaleway.com>
    Acked-by: default avatarJason Wang <jasowang@redhat.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    4b663366