linux-kernel - Re: [PATCH] sysctl: min-max range check is broken

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Date:	Fri, 6 Feb 2009 00:19:34 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Shakesh Jain <shjain@...mai.com>, ShakeshJain@...mai.com,
	linux-kernel@...r.kernel.org, juhlenko@...mai.com
Subject: Re: [PATCH] sysctl: min-max range check is broken

On Thu, Feb 05, 2009 at 12:55:56PM -0800, Eric W. Biederman wrote:
> Andrew Morton <akpm@...ux-foundation.org> writes:
> 
> > On Wed, 4 Feb 2009 00:40:22 -0800
> > Shakesh Jain <shjain@...mai.com>, ShakeshJain@...mai.com wrote:
> >
> >> do_proc_dointvec_minmax_conv() which gets callled from
> >> proc_dointvec_minmax proc_handler doesn't increment the pointer to
> >> the 'min' (extra1) and 'max' (extra2) after each range check which
> >> results in doing the check against same set of min and max values.
> >> 
> >> This breaks the range checking for those sysctl's where you can
> >> write multiple values to /proc with each variable having its own range
> >> specification.
> 
> I just did a quick grep for .extra1 and I don't see anywhere we use
> the code as described.
> 
> >> It seems to be implemented for the sysctl() system call strategy in
> >> sysctl_intvec() where min and max are treated as arrays.
> 
> Yep.  There is an inconsistency here.  Given how sysctl is used and
> tested, and the fact I could not find where it appears that anyone is
> passing an array into min/max I would say that the proc version is
> correct and the sysctl version is wrong.
> 
> The untested patch below looks like it will fix the this.
> 
> I don't know if there are any cases where we use minmax with an array
> of integers but I don't see the point of using an array of minmax
> values at this point.

Multiple values, each one is bounded by it's own set of values.

> For the original sysctl design it may have made
> some sense.  New code should be one value per file.

So leave them alone.

> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2916,9 +2916,9 @@ int sysctl_intvec(struct ctl_table *table,
>  			int value;
>  			if (get_user(value, vec + i))
>  				return -EFAULT;
> -			if (min && value < min[i])
> +			if (min && value < *min)
>  				return -EINVAL;
> -			if (max && value > max[i])
> +			if (max && value > *max)
>  				return -EINVAL;

Correct way is:

	min[i] <= val[i] <= max[i]

This is what sysctl_intvec() does.
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