On 11/30/15 4:18 PM, Andrew Morton wrote:
> On Mon, 30 Nov 2015 16:04:36 -0800 Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
>>>>> +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
>>>>> + {
>>>>> + .procname = "mmap_rnd_bits",
>>>>> + .data = &mmap_rnd_bits,
>>>>> + .maxlen = sizeof(mmap_rnd_bits),
>>>>> + .mode = 0600,
>>>>> + .proc_handler = proc_dointvec_minmax,
>>>>> + .extra1 = (void *) &mmap_rnd_bits_min,
>>>>> + .extra2 = (void *) &mmap_rnd_bits_max,
>>>>
>>>> hm, why the typecasts? They're unneeded and are omitted everywhere(?)
>>>> else in kernel/sysctl.c.
>>>
>>> Oh. Casting away constness.
>>>
>>> What's the thinking here? They can change at any time so they aren't
>>> const so we shouldn't declare them to be const?
>>
>> The _min and _max values shouldn't be changing: they're decided based
>> on the various CONFIG options that calculate the valid min/maxes. Only
>> mmap_rnd_bits itself should be changing.
>
> hmpf.
>
> From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Subject: include/linux/sysctl.h: make ctl_table.extra1/2 const
>
> Nothing should be altering these values. Declare the pointed-to values to
> be const so we can actually use const values.
>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Daniel Cashman <dcashman@xxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>
> include/linux/sysctl.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff -puN include/linux/sysctl.h~a include/linux/sysctl.h
> --- a/include/linux/sysctl.h~a
> +++ a/include/linux/sysctl.h
> @@ -111,8 +111,8 @@ struct ctl_table
> struct ctl_table *child; /* Deprecated */
> proc_handler *proc_handler; /* Callback for text formatting */
> struct ctl_table_poll *poll;
> - void *extra1;
> - void *extra2;
> + const void *extra1;
> + const void *extra2;
> };
>
> struct ctl_node {
> diff -puN kernel/sysctl.c~a kernel/sysctl.c
> _
This looks good to me, thanks! I hadn't gone through all of the uses of
extra1 and extra2, nor did I think the change herein was conceptually a
part of mine, so I casted-away in order to indicate intent, while
leaving the change here as a possibility if ctl_table could be altered
for all use-cases.
Thank You,
Dan
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