Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932700AbbDNPde (ORCPT ); Tue, 14 Apr 2015 11:33:34 -0400 Received: from e19.ny.us.ibm.com ([129.33.205.209]:33608 "EHLO e19.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755472AbbDNPdZ (ORCPT ); Tue, 14 Apr 2015 11:33:25 -0400 Message-ID: <552D333E.8050406@linux.vnet.ibm.com> Date: Tue, 14 Apr 2015 10:33:18 -0500 From: Thomas Falcon User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: David Gibson , anton@au1.ibm.com, benh@kernel.crashing.org, michael@ellerman.id.au CC: linux-kernel@vger.kernel.org, linuxppc-dev@vger.kernel.org Subject: Re: [PATCH] ibmveth: Fix off-by-one error in ibmveth_change_mtu() References: <1428903586-21442-1-git-send-email-david@gibson.dropbear.id.au> In-Reply-To: <1428903586-21442-1-git-send-email-david@gibson.dropbear.id.au> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15041415-0013-0000-0000-000000640119 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2417 Lines: 62 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) Thanks, Tom > Signed-off-by: David Gibson > --- > drivers/net/ethernet/ibm/ibmveth.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c > index cd7675a..3aa280a 100644 > --- a/drivers/net/ethernet/ibm/ibmveth.c > +++ b/drivers/net/ethernet/ibm/ibmveth.c > @@ -1257,7 +1257,7 @@ static int ibmveth_change_mtu(struct net_device *dev, int new_mtu) > for (i = 0; i < IBMVETH_NUM_BUFF_POOLS; i++) { > adapter->rx_buff_pool[i].active = 1; > > - if (new_mtu_oh < adapter->rx_buff_pool[i].buff_size) { > + if (new_mtu_oh <= adapter->rx_buff_pool[i].buff_size) { > dev->mtu = new_mtu; > vio_cmo_set_dev_desired(viodev, > ibmveth_get_desired_dma -- Tom Falcon Software Engineer IBM LTC Austin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/