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SubjectRe: [PATCH] ibmveth: Fix off-by-one error in ibmveth_change_mtu()
On Tue, Apr 14, 2015 at 10:33:18AM -0500, Thomas Falcon wrote:
> On 04/13/2015 12:39 AM, David Gibson wrote:
> > AFAIK the PAPR document which defines the virtual device interface used by
> > the ibmveth driver doesn't specify a specific maximum MTU. So, in the
> > ibmveth driver, the maximum allowed MTU is determined by the maximum
> > allocated buffer size of 64k (corresponding to one page in the common case)
> > minus the per-buffer overhead IBMVETH_BUFF_OH (which has value 22 for 14
> > bytes of ethernet header, plus 8 bytes for an opaque handle).
> >
> > This suggests a maximum allowable MTU of 65514 bytes, but in fact the
> > driver only permits a maximum MTU of 65513. This is because there is a <
> > instead of an <= in ibmveth_change_mtu(), which only permits an MTU which
> > is strictly smaller than the buffer size, rather than allowing the buffer
> > to be completely filled.
> >
> > This patch fixes the buglet.
>
>
> The same expression is made using < just a few lines above. Shouldn't this be changed to <= too?
>
> @@ -1238,7 +1238,7 @@ static int ibmveth_change_mtu(struct net_device *dev, int new_mtu)
> return -EINVAL;
>
> for (i = 0; i < IBMVETH_NUM_BUFF_POOLS; i++)
> - if (new_mtu_oh < adapter->rx_buff_pool[i].buff_size)
> + if (new_mtu_oh <= adapter->rx_buff_pool[i].buff_size)
> break;
>
> if (i == IBMVETH_NUM_BUFF_POOLS)

Yes, yes it should.

Good catch, thanks.

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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