Re: [Qemu-devel] [PATCH 1/2] CVE-2015-1779: incrementally decode websocket frames

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> > +    if (input->offset < *payload_remain) {
> > +        *payload_size = input->offset - (input->offset % 4);
> > +    } else {
> > +        *payload_size = input->offset;
> 
> This can set *payload_size to a value larger than
> *payload_remain, if the input buffer happens to contain
> further data after the end of this packet...
> 
> > +    }
> > +    if (*payload_size == 0) {
> >          return 0;
> >      }
> > -
> > -    *payload = input->buffer + header_size;
> > +    *payload_remain -= *payload_size;
> 
> ...at which point this will end up making
> *payload_remain negative. Disconnection happens shortly
> afterwards.
> 
> Should the line
>     *payload_size = input->offset;
> actually read
>     *payload_size = *payload_remain;
> 
> ?
> 
> Making that change appears to fix the novnc disconnects
> that Gerd reports.

Confirmed.  Fixes the issues I've seen in testing and looks sensible to
me.  Comment from Daniel would be nice, especially as I know next to
nothing about websockets, but he seems to be off into the easter
holidays already.

So, with -rc2 waiting for this (and being late already) I think I'll
squash in the incremental fix and prepare a pull request even without
Daniels ack ...

cheers,
  Gerd