Re: [Qemu-devel] possible denial of service via VNC

[Peter Lieven]

On 30.06.2014 09:33, Gerd Hoffmann wrote:
> On So, 2014-06-29 at 14:16 +0200, Peter Lieven wrote:
> > Hi,
> >
> > while debugging a VNC issue I found this:
> >
> >      case VNC_MSG_CLIENT_CUT_TEXT:
> >          if (len == 1)
> >              return 8;
> >
> >          if (len == 8) {
> >              uint32_t dlen = read_u32(data, 4);
> >              if (dlen > 0)
> >                  return 8 + dlen;
> >          }
> >
> >          client_cut_text(vs, read_u32(data, 4), data + 8);
> >          break;
> >
> > in protocol_client_msg().
> >
> > Is this really a good idea? This allows for letting the vs->input buffer to grow
> > up to 2^32 + 8 byte which will possibly result in an out of memory condition.
> Applying a limit there looks reasonable to me.  Patches welcome.
> As this is text only a megabyte should be more than enough for all
> practical purposes.  Question is what to do when the limit is exceeded?
> Disconnect?  Read & throw away?

I would also think something in the order of megabytes should be fine.
I would vote for disconnect as soon as the limit specified is too big. Otherwise
we had to rewrite the whole receive logic which could introduce additional
bugs.

Peter

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Mit freundlichen Grüßen

Peter Lieven

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