netdev - Re: [PATCH v1] drivers/vhost/vhost: fix overflow checks in vhost

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Message-ID: <bc387a08-e5ad-7a6b-2af4-61f79090277b@yandex-team.ru>
Date:   Thu, 8 Dec 2022 10:21:09 +0300
From:   Daniil Tatianin <d-tatianin@...dex-team.ru>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] drivers/vhost/vhost: fix overflow checks in
 vhost_overflow

On 12/7/22 6:01 PM, Michael S. Tsirkin wrote:
> On Wed, Dec 07, 2022 at 04:46:31PM +0300, Daniil Tatianin wrote:
>> The if statement would erroneously check for > ULONG_MAX, which could
>> never evaluate to true. Check for equality instead.
>>
>> Found by Linux Verification Center (linuxtesting.org) with the SVACE
>> static analysis tool.
>>
>> Signed-off-by: Daniil Tatianin <d-tatianin@...dex-team.ru>
> 
> It can trigger on a 32 bit system. I'd also expect more analysis
> of the code flow than "this can not trigger switch to a condition
> that can" to accompany a patch.

Oops, my bad. It can trigger on 32 bit indeed. Sorry, completely 
overlooked that.

Thanks

>> ---
>>   drivers/vhost/vhost.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index 40097826cff0..8df706e7bc6c 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -730,7 +730,7 @@ static bool log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
>>   /* Make sure 64 bit math will not overflow. */
>>   static bool vhost_overflow(u64 uaddr, u64 size)
>>   {
>> -	if (uaddr > ULONG_MAX || size > ULONG_MAX)
>> +	if (uaddr == ULONG_MAX || size == ULONG_MAX)
>>   		return true;
>>   
>>   	if (!size)
>> -- 
>> 2.25.1
>