linux-kernel - Re: [PATCH] Fixed division by zero bug in kernel/padata.c

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 2 Jul 2010 17:24:13 +0400
From:	Dan Kruchinin <dkruchinin@....org>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH] Fixed division by zero bug in kernel/padata.c

No problem. Here is fixed patch:
--
 When boot CPU(typically CPU #0) is excluded from padata cpumask and
 user enters halt command from console, kernel faults on division by zero;
 This occurs because during the halt kernel shuts down each non-boot CPU one
 by one. After it shuts down the last CPU that is set in the padata cpumask,
 the only working CPU in the system is a boot CPU(#0) and it's the only CPU that
 is set in the cpu_active_mask. Hence when padata_cpu_callback calls
 __padata_remove_cpu(and hence padata_alloc_pd) it appears that padata
cpumask and
 cpu_active mask aren't intersect. Hence the following code in
padata_alloc_pd causes
 a DZ error exception:
  cpumask_and(pd->cpumask, cpumask, cpu_active_mask); // pd->cpumask
will be empty
  ...
  num_cpus = cpumask_weight(pd->cpumask); // num_cpus = 0
  pd->max_seq_nr = (MAX_SEQ_NR / num_cpus) * num_cpus - 1; // DZ!


Signed-off-by: Dan Kruchinin <dkruchinin@....org>
---
 kernel/padata.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index fdd8ae6..dcddac0 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -435,6 +435,9 @@ static struct parallel_data
*padata_alloc_pd(struct padata_instance *pinst,
 	}

 	num_cpus = cpumask_weight(pd->cpumask);
+	if (!num_cpus)
+		goto err_free_cpumask;
+
 	pd->max_seq_nr = (MAX_SEQ_NR / num_cpus) * num_cpus - 1;

 	setup_timer(&pd->timer, padata_reorder_timer, (unsigned long)pd);
@@ -446,6 +449,8 @@ static struct parallel_data
*padata_alloc_pd(struct padata_instance *pinst,

 	return pd;

+err_free_cpumask:
+	free_cpumask_var(pd->cpumask);
 err_free_queue:
 	free_percpu(pd->queue);
 err_free_pd:
-- 
1.7.1


On Fri, Jul 2, 2010 at 4:56 PM, Steffen Klassert
<steffen.klassert@...unet.com> wrote:
> On Fri, Jul 02, 2010 at 03:59:54PM +0400, Dan Kruchinin wrote:
>>  When boot CPU(typically CPU #0) is excluded from padata cpumask and
>>  user enters halt command from console, kernel faults on division by zero;
>>  This occurs because during the halt kernel shuts down each non-boot CPU one
>>  by one and after it shuts down the last CPU that is set in the padata cpumask,
>>  the only working CPU in the system is a boot CPU(#0) and it's the only CPU that
>>  is set in the cpu_active_mask. Hence when padata_cpu_callback calls
>>  __padata_remove_cpu(which calls padata_alloc_pd) it appears that
>> padata cpumask and
>>  cpu_active_mask aren't intersect. Hence the following code in
>> padata_alloc_pd causes
>>  a DZ error exception:
>>   cpumask_and(pd->cpumask, cpumask, cpu_active_mask); // pd->cpumask
>> will be empty
>>   ...
>>   num_cpus = cpumask_weight(pd->cpumask); // num_cpus = 0
>>   pd->max_seq_nr = (MAX_SEQ_NR / num_cpus) * num_cpus - 1; // DZ!
>>
>
> Good catch!
>
>>
>> Signed-off-by: Dan Kruchinin <dkruchinin@....org>
>> ---
>>  kernel/padata.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/kernel/padata.c b/kernel/padata.c
>> index fdd8ae6..dbe6d26 100644
>> --- a/kernel/padata.c
>> +++ b/kernel/padata.c
>> @@ -434,7 +434,7 @@ static struct parallel_data
>> *padata_alloc_pd(struct padata_instance *pinst,
>>               atomic_set(&queue->num_obj, 0);
>>       }
>>
>> -     num_cpus = cpumask_weight(pd->cpumask);
>> +     num_cpus = cpumask_weight(pd->cpumask) + 1;
>>       pd->max_seq_nr = (MAX_SEQ_NR / num_cpus) * num_cpus - 1;
>>
>
> num_cpus should stay the number of cpus in this cpumask, this is required
> to handle a smooth overrun of the sequence numbers.
> I think it's better to return with an error and to stop the instance
> if somebody takes away the last cpu in our cpumask. We can't run with an
> empty cpumask anyway.
>
> Let us look again at this on monday.
>
> Thanks again for catching this,
>
> Steffen
>



-- 
W.B.R.
Dan Kruchinin
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/