Subject: Re: RFC: [PATCH 2/3] netdevice: Fix promiscuity and allmulti overflow

From: Wang Chen <[email-masked]>
Date: Mon, 16 Jun 2008 17:51:21 +0800

Patrick McHardy said the following on 2008-6-16 17:38:
> Wang Chen wrote:
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 5829630..a3c692d 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -2753,10 +2753,20 @@ static void __dev_set_promiscuity(struct
>> net_device *dev, int inc)
>>  
>>      ASSERT_RTNL();
>>  
>> +    dev->flags |= IFF_PROMISC;
>>      if ((dev->promiscuity += inc) == 0)
>> -        dev->flags &= ~IFF_PROMISC;
>> -    else
>> -        dev->flags |= IFF_PROMISC;
>> +        /*
>> +         * Avoid overflow.
>> +         * If inc causes overflow, ignore it and warn user.
>> +         */
>> +        if (inc < 0)
>> +            dev->flags &= ~IFF_PROMISC;
>> +        else {
>> +            dev->promiscuity -= inc;
>> +            printk(KERN_ERR "%s: promiscuity touches roof, "
>> +                "set promiscuity failed, promiscuity feature "
>> +                "of device will be broken.\n");
>> +        }
> 
> Additional parens around the inner block would make this more
> readable.
> 

Will fix.

> I question the need for this though, userspace can only trigger
> an increase/decrease by one no matter how often it enables
> the ALLMULTI/PROMISC flags, and I doubt any codepath in the
> kernel would lead to an overflow.
> 

How about mif6_add()?
Do we have a limit for mif6?

> If this can really happen it would be better to leave the
> counter untouched and return an error, we already have too
> many device operations that might fail more or less silently.
> 

This can be done.