linux-kernel - Re: [Patch 1/3] sysctl: refactor integer handling proc code

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Date:	Tue, 13 Apr 2010 15:35:44 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
CC:	linux-kernel@...r.kernel.org,
	Octavian Purdila <opurdila@...acom.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	penguin-kernel@...ove.SAKURA.ne.jp, netdev@...r.kernel.org,
	Neil Horman <nhorman@...driver.com>, ebiederm@...ssion.com,
	David Miller <davem@...emloft.net>
Subject: Re: [Patch 1/3] sysctl: refactor integer handling proc code

Alexey Dobriyan wrote:
> On Mon, Apr 12, 2010 at 06:04:04AM -0400, Amerigo Wang wrote:
>> As we are about to add another integer handling proc function a little
>> bit of cleanup is in order: add a few helper functions to improve code
>> readability and decrease code duplication.
>>
>> In the process a bug is also fixed: if the user specifies a number
>> with more then 20 digits it will be interpreted as two integers
>> (e.g. 10000...13 will be interpreted as 100.... and 13).
> 
> ULONG_MAX is not 22 digits always.
> 
> The fix is to not rely on simple_strtoul()
> 
> I guess it's time to finally remove it. :-(


Or use strict_strtoul()?

> 
> Also, it's better to copy_from user stuff once.
> Without looking at non-trivial users, one page should be enough.

It seems that all proc code assumes that the input buffer will
not exceed one page size.


> 
>> Behavior for EFAULT handling was changed as well. Previous to this
>> patch, when an EFAULT error occurred in the middle of a write
>> operation, although some of the elements were set, that was not
>> acknowledged to the user (by shorting the write and returning the
>> number of bytes accepted). EFAULT is now treated just like any other
>> errors by acknowledging the amount of bytes accepted.
> 
>> +static int proc_skip_wspace(char __user **buf, size_t *size)
>> +{
>> +	char c;
>> +
>> +	while (*size) {
>> +		if (get_user(c, *buf))
>> +			return -EFAULT;
>> +		if (!isspace(c))
>> +			break;
>> +		(*size)--;
>> +		(*buf)++;
>> +	}
>> +
>> +	return 0;
>> +}
> 
> yeah, copy_from_user once, so we won't have this.

Ok.

> 
>> +static bool isanyof(char c, const char *v, unsigned len)
> 
> A what?
> this is memchr()
> 

Hmm, right, it should be memchr(v, c, len).

Thanks!

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