netdev - Re: [net-next 01/14] lib: cpu_rmap: Avoid use after free on rmap->obj array entries

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Date:   Wed, 22 Mar 2023 11:43:08 +0200
From:   Eli Cohen <elic@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>, Saeed Mahameed <saeed@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Saeed Mahameed <saeedm@...dia.com>, netdev@...r.kernel.org,
        Tariq Toukan <tariqt@...dia.com>
Subject: Re: [net-next 01/14] lib: cpu_rmap: Avoid use after free on rmap->obj
 array entries


On 22/03/2023 5:38, Jakub Kicinski wrote:
> On Mon, 20 Mar 2023 10:51:31 -0700 Saeed Mahameed wrote:
>> From: Eli Cohen <elic@...dia.com>
>>
>> When calling irq_set_affinity_notifier() with NULL at the notify
>> argument, it will cause freeing of the glue pointer in the
>> corresponding array entry but will leave the pointer in the array. A
>> subsequent call to free_irq_cpu_rmap() will try to free this entry again
>> leading to possible use after free.
>>
>> Fix that by setting NULL to the array entry and checking that we have
>> non-zero at the array entry when iterating over the array in
>> free_irq_cpu_rmap().
> Commit message needs some work. Are you trying to make double
> free_irq_cpu_rmap() work fine because of callers?

Some callers may want to call irq_set_affinity_notifier() for a specific 
vector and then call free_irq_cpu_rmap() to to free the struct cpu_rmap 
allocation.  This is a valid scenario as both 
irq_set_affinity_notifier() are exported. This sequence. This sequence 
of calls does not happen in the current kernel but my other patches in 
the series do.

I will try to improve the commit message.

>   Are there problems
> with error path of irq_cpu_rmap_add()? I can tell what you're trying
> to prevent but not why.
No, as explained above.
>
>> Fixes: c39649c331c7 ("lib: cpu_rmap: CPU affinity reverse-mapping")
> What is this Fixes tag doing in a net-next patch :S
> If it can be triggered it needs to go to net.
It can't be triggered but with my subsequent patches it could.
>
>> Signed-off-by: Eli Cohen <elic@...dia.com>
>> Signed-off-by: Saeed Mahameed <saeedm@...dia.com>
>> ---
>>   lib/cpu_rmap.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/cpu_rmap.c b/lib/cpu_rmap.c
>> index f08d9c56f712..e77f12bb3c77 100644
>> --- a/lib/cpu_rmap.c
>> +++ b/lib/cpu_rmap.c
>> @@ -232,7 +232,8 @@ void free_irq_cpu_rmap(struct cpu_rmap *rmap)
>>   
>>   	for (index = 0; index < rmap->used; index++) {
> After looking at this code for 10min - isn't the problem that used
> is never decremented on the error path?
>
> I don't see a way to remove from the map so it can't be sparse.
This call, irq_set_affinity_notifier(glue->notify.irq, NULL) can be made 
by drivers.
>
>>   		glue = rmap->obj[index];
>> -		irq_set_affinity_notifier(glue->notify.irq, NULL);
>> +		if (glue)
>> +			irq_set_affinity_notifier(glue->notify.irq, NULL);
>>   	}
>>   
>>   	cpu_rmap_put(rmap);
>> @@ -268,6 +269,7 @@ static void irq_cpu_rmap_release(struct kref *ref)
>>   		container_of(ref, struct irq_glue, notify.kref);
>>   
>>   	cpu_rmap_put(glue->rmap);
>> +	glue->rmap->obj[glue->index] = NULL;
>>   	kfree(glue);
>>   }
>>   
>> @@ -297,6 +299,7 @@ int irq_cpu_rmap_add(struct cpu_rmap *rmap, int irq)
>>   	rc = irq_set_affinity_notifier(irq, &glue->notify);
>>   	if (rc) {
>>   		cpu_rmap_put(glue->rmap);
>> +		rmap->obj[glue->index] = NULL;
>>   		kfree(glue);
>>   	}
>>   	return rc;