Re: [PATCH -next v2] cred: conditionally declare groups-related functions

[Paul Moore]

On Mon, Jun 25, 2018 at 2:56 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote:
> The groups-related functions declared in include/linux/cred.h are
> defined in kernel/groups.c, which is compiled only when
> CONFIG_MULTIUSER=y. Move all these function declarations under #ifdef
> CONFIG_MULTIUSER to help avoid accidental usage in contexts where
> CONFIG_MULTIUSER might be disabled.
>
> This patch also adds a fallback for groups_search(). Currently this
> function is only called from kernel/groups.c itself and
> keys/permissions.c, which depends on CONFIG_MULTIUSER. However, the
> audit subsystem (which does not depend on CONFIG_MULTIUSER) calls this
> function in -next, so the fallback will be needed to avoid compilation
> errors or ugly workarounds.
>
> See also:
> https://lkml.org/lkml/2018/6/20/670
> https://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/audit.git/commit/?h=next&id=af85d1772e31fed34165a1b3decef340cf4080c0
>
> Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
> ---
>  include/linux/cred.h | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/cred.h b/include/linux/cred.h
> index 631286535d0f..7eed6101c791 100644
> --- a/include/linux/cred.h
> +++ b/include/linux/cred.h
> @@ -65,6 +65,12 @@ extern void groups_free(struct group_info *);
>
>  extern int in_group_p(kgid_t);
>  extern int in_egroup_p(kgid_t);
> +extern int groups_search(const struct group_info *, kgid_t);
> +
> +extern int set_current_groups(struct group_info *);
> +extern void set_groups(struct cred *, struct group_info *);
> +extern bool may_setgroups(void);
> +extern void groups_sort(struct group_info *);
>  #else
>  static inline void groups_free(struct group_info *group_info)
>  {
> @@ -78,12 +84,11 @@ static inline int in_egroup_p(kgid_t grp)
>  {
>          return 1;
>  }
> +static inline int groups_search(const struct group_info *group_info, kgid_t grp)
> +{
> +       return 1;
> +}
>  #endif
> -extern int set_current_groups(struct group_info *);
> -extern void set_groups(struct cred *, struct group_info *);
> -extern int groups_search(const struct group_info *, kgid_t);
> -extern bool may_setgroups(void);
> -extern void groups_sort(struct group_info *);

I was going through the list of functions to make sure it was safe to
move all of these under CONFIG_MULTIUSER and I believe there may be an
issue with key_task_permission() and groups_search(), specifically one
can disable CONFIG_MULTIUSER yet keep CONFIG_KEYS enabled.

I'm going to guess that the fix is going to be to have CONFIG_KEYS
depend on CONFIG_MULTIUSER, but I would talk with the keys folks (I've
CC'd David Howells) to see what they would prefer.

-- 
paul moore
www.paul-moore.com