On Sun, 2015-05-31 at 21:42 -0700, David Miller wrote:
> From: Eric Dumazet <eric.duma...@gmail.com>
> Date: Sat, 30 May 2015 09:16:53 -0700
>
> > From: Eric Dumazet <eduma...@google.com>
> >
> > We have two problems in UDP stack related to bogus checksums :
> >
> > 1) We return -EAGAIN to application even if receive queue is not empty.
> > This breaks applications using edge trigger epoll()
> >
> > 2) Under UDP flood, we can loop forever without yielding to other
> > processes, potentially hanging the host, especially on non SMP.
> >
> >
> > This patch is an attempt to make things better.
> >
> > We might in the future add extra support for rt applications
> > wanting to better control time spent doing a recv() in a hostile
> > environment. For example we could validate checksums before queuing
> > packets in socket receive queue.
> >
> > Signed-off-by: Eric Dumazet <eduma...@google.com>
>
> Yeah this looks correct, applied and queued up for -stable.
>
> Thanks!
Thanks David
It seems MSG_PEEK support is broken with checksums and truncated data:
Multiple threads could operate on same skb and
__udp_lib_checksum_complete() / __skb_checksum_complete() can do bad
things.
Tom, any idea how this could be fixed ? It looks you added this bug in
3.16
/*
* If checksum is needed at all, try to do it while copying the
* data. If the data is truncated, or if we only want a partial
* coverage checksum (UDP-Lite), do it before the copy.
*/
if (copied < ulen || UDP_SKB_CB(skb)->partial_cov) {
if (udp_lib_checksum_complete(skb))
goto csum_copy_err;
}
...
__sum16 __skb_checksum_complete(struct sk_buff *skb)
{
__wsum csum;
__sum16 sum;
csum = skb_checksum(skb, 0, skb->len, 0);
/* skb->csum holds pseudo checksum */
sum = csum_fold(csum_add(skb->csum, csum));
if (likely(!sum)) {
if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
!skb->csum_complete_sw)
netdev_rx_csum_fault(skb->dev);
}
/* Save full packet checksum */
skb->csum = csum;
skb->ip_summed = CHECKSUM_COMPLETE;
skb->csum_complete_sw = 1;
skb->csum_valid = !sum;
return sum;
}
Maybe adding a 'readonly' bool param to __skb_checksum_complete() ?
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