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Message-ID: <d3fe83e4-db71-6180-40e8-e0cfaf52be34@yandex-team.ru> Date: Thu, 16 Feb 2023 09:42:13 +0300 From: Daniil Tatianin <d-tatianin@...dex-team.ru> To: Manish Chopra <manishc@...vell.com>, Simon Horman <simon.horman@...igine.com> Cc: Ariel Elior <aelior@...vell.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Yuval Mintz <Yuval.Mintz@...gic.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [EXT] Re: [PATCH v0] qed/qed_dev: guard against a possible division by zero On 2/16/23 12:20 AM, Manish Chopra wrote: >> -----Original Message----- >> From: Daniil Tatianin <d-tatianin@...dex-team.ru> >> Sent: Tuesday, February 14, 2023 12:53 PM >> To: Simon Horman <simon.horman@...igine.com> >> Cc: Ariel Elior <aelior@...vell.com>; Manish Chopra >> <manishc@...vell.com>; David S. Miller <davem@...emloft.net>; Eric >> Dumazet <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>; Paolo >> Abeni <pabeni@...hat.com>; Yuval Mintz <Yuval.Mintz@...gic.com>; >> netdev@...r.kernel.org; linux-kernel@...r.kernel.org >> Subject: [EXT] Re: [PATCH v0] qed/qed_dev: guard against a possible division >> by zero >> >> External Email >> >> ---------------------------------------------------------------------- >> >> >> On 2/9/23 2:13 PM, Simon Horman wrote: >>> On Thu, Feb 09, 2023 at 01:38:13PM +0300, Daniil Tatianin wrote: >>>> Previously we would divide total_left_rate by zero if num_vports >>>> happened to be 1 because non_requested_count is calculated as >>>> num_vports - req_count. Guard against this by explicitly checking for >>>> zero when doing the division. >>>> >>>> Found by Linux Verification Center (linuxtesting.org) with the SVACE >>>> static analysis tool. >>>> >>>> Fixes: bcd197c81f63 ("qed: Add vport WFQ configuration APIs") >>>> Signed-off-by: Daniil Tatianin <d-tatianin@...dex-team.ru> >>>> --- >>>> drivers/net/ethernet/qlogic/qed/qed_dev.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/net/ethernet/qlogic/qed/qed_dev.c >>>> b/drivers/net/ethernet/qlogic/qed/qed_dev.c >>>> index d61cd32ec3b6..90927f68c459 100644 >>>> --- a/drivers/net/ethernet/qlogic/qed/qed_dev.c >>>> +++ b/drivers/net/ethernet/qlogic/qed/qed_dev.c >>>> @@ -5123,7 +5123,7 @@ static int qed_init_wfq_param(struct qed_hwfn >>>> *p_hwfn, >>>> >>>> total_left_rate = min_pf_rate - total_req_min_rate; >>>> >>>> - left_rate_per_vp = total_left_rate / non_requested_count; >>>> + left_rate_per_vp = total_left_rate / (non_requested_count ?: 1); >>> >>> I don't know if num_vports can be 1. >>> But if it is then I agree that the above will be a divide by zero. >>> >>> I do, however, wonder if it would be better to either: >>> >>> * Treat this case as invalid and return with -EINVAL if num_vports is >>> 1; or >> I think that's a good idea considering num_vports == 1 is indeed an invalid >> value. >> I'd like to hear a maintainer's opinion on this. > > Practically, this flow will only hit with presence of SR-IOV VFs. In that case it's > always expected to have num_vports > 1. In that case, should we add a check and return with -EINVAL otherwise? Thank you! >>> * Skip both the calculation immediately above and the code >>> in the if condition below, which is the only place where >>> the calculated value is used, if num_vports is 1. >>> I don't think the if clause makes much sense if num_vports is >>> one.left_rate_per_vp is also used below the if clause, it is assigned >>> to >> .min_speed in a for loop. Looking at that code division by 1 seems to make >> sense to me in this case. >>> >>>> if (left_rate_per_vp < min_pf_rate / QED_WFQ_UNIT) { >>>> DP_VERBOSE(p_hwfn, NETIF_MSG_LINK, >>>> "Non WFQ configured vports rate [%d Mbps] is less >> than one >>>> percent of configured PF min rate[%d Mbps]\n", >>>> -- >>>> 2.25.1 >>>>
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