Re: [Qemu-devel] [PATCH 1/2] net: pcnet: check rx/tx descriptor ring length

[P J P <ppandit@redhat.com>]

  Hello Jason,

+-- On Fri, 30 Sep 2016, Jason Wang wrote --+
| On 2016年09月30日 02:57, P J P wrote:
| > The AMD PC-Net II emulator has set of control and status(CSR)
| > registers. Of these, CSR76 and CSR78 hold receive and transmit
| > descriptor ring length respectively. This ring length could range
| > from 1 to 65535. Setting ring length to zero leads to an infinite
| > loop in pcnet_rdra_addr. Add check to avoid it.
| 
| In this case, we only need to protect RCVRL I believe? (since XMTRL were not
| used).

  XMTRL is not used in this case, but could be prone to similar issues. For 
ex.

    static void pcnet_transmit(PCNetState *s)
    {
        int count = CSR_XMTRL(s) - 1;
        ...
        if (count--)
            goto txagain;
    }

If CSR_XMTRL is set to zero(0), 'count' would never reach zero and function 
would continue to jump to 'txagain'.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
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