netdev - Re: [PATCH net-next] net: remove redundant input checks in SIOCSIFTXQLEN case of dev

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Message-ID: <b75a52cb-2c7b-2108-f256-1ebb93a82f7b@mellanox.com>
Date:   Sun, 22 Jul 2018 10:29:24 +0300
From:   Tariq Toukan <tariqt@...lanox.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>
Cc:     David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        eranbe@...lanox.com
Subject: Re: [PATCH net-next] net: remove redundant input checks in
 SIOCSIFTXQLEN case of dev_ifsioc



On 19/07/2018 8:21 PM, Cong Wang wrote:
> On Thu, Jul 19, 2018 at 7:50 AM Tariq Toukan <tariqt@...lanox.com> wrote:
>> --- a/net/core/dev_ioctl.c
>> +++ b/net/core/dev_ioctl.c
>> @@ -282,14 +282,7 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, unsigned int cmd)
>>                  return dev_mc_del_global(dev, ifr->ifr_hwaddr.sa_data);
>>
>>          case SIOCSIFTXQLEN:
>> -               if (ifr->ifr_qlen < 0)
>> -                       return -EINVAL;
> 
> Are you sure we can remove this if check too?
> 
> The other one is safe to remove.
> 

Hmm, let's see:
dev_change_tx_queue_len gets unsigned long new_len, any negative value 
passed is interpreted as a very large number, then we test:
if (new_len != (unsigned int)new_len)

This test returns true if range of unsigned long is larger than range of 
unsigned int. AFAIK these ranges are Arch dependent and there is no 
guarantee this holds.

Right?