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
_
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