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    SubjectRe: [PATCH 1/2] proc/sysctl: add shared variables for range check
    On Mon, Apr 8, 2019 at 3:09 PM Matteo Croce <mcroce@redhat.com> wrote:
    >
    > In the sysctl code the proc_dointvec_minmax() function is often used to
    > validate the user supplied value between an allowed range. This function
    > uses the extra1 and extra2 members from struct ctl_table as minimum and
    > maximum allowed value.
    >
    > On sysctl handler declaration, in every source file there are some readonly
    > variables containing just an integer which address is assigned to the
    > extra1 and extra2 members, so the sysctl range is enforced.
    >
    > The special values 0, 1 and INT_MAX are very often used as range boundary,
    > leading duplication of variables like zero=0, one=1, int_max=INT_MAX in
    > different source files:
    >
    > $ git grep -E '\.extra[12].*&(zero|one|int_max)' |wc -l
    > 261
    >
    > This patch adds three variables for the most commonly used values, so they
    > can be referenced instead of creating a local one for every object file.
    >
    > Signed-off-by: Matteo Croce <mcroce@redhat.com>

    Oh, and for this patch: Yes please; let's get everyone to use these
    instead of littering the kernel with (non-const!) copies of the same
    thing. :)

    Acked-by: Kees Cook <keescook@chromium.org>

    -Kees

    > ---
    > fs/proc/proc_sysctl.c | 5 +++++
    > include/linux/sysctl.h | 4 ++++
    > 2 files changed, 9 insertions(+)
    >
    > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
    > index d65390727541..e7a96169fced 100644
    > --- a/fs/proc/proc_sysctl.c
    > +++ b/fs/proc/proc_sysctl.c
    > @@ -21,6 +21,11 @@ static const struct inode_operations proc_sys_inode_operations;
    > static const struct file_operations proc_sys_dir_file_operations;
    > static const struct inode_operations proc_sys_dir_operations;
    >
    > +/* shared constants to be used in various sysctls */
    > +const int sysctl_zero = 0;
    > +const int sysctl_one = 1;
    > +const int sysctl_int_max = INT_MAX;
    > +
    > /* Support for permanently empty directories */
    >
    > struct ctl_table sysctl_mount_point[] = {
    > diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
    > index b769ecfcc3bd..f3b191799747 100644
    > --- a/include/linux/sysctl.h
    > +++ b/include/linux/sysctl.h
    > @@ -37,6 +37,10 @@ struct ctl_table_root;
    > struct ctl_table_header;
    > struct ctl_dir;
    >
    > +extern const int sysctl_zero;
    > +extern const int sysctl_one;
    > +extern const int sysctl_int_max;
    > +
    > typedef int proc_handler (struct ctl_table *ctl, int write,
    > void __user *buffer, size_t *lenp, loff_t *ppos);
    >
    > --
    > 2.21.0
    >


    --
    Kees Cook

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