Re: [PATCH -next v2] cred: conditionally declare groups-related functions
po 25. 6. 2018 o 23:04 Paul Moore <paul(a)paul-moore.com> napísal(a):
On Mon, Jun 25, 2018 at 2:56 AM Ondrej Mosnacek <omosnace(a)redhat.com> 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/...
>
> Reported-by: Randy Dunlap <rdunlap(a)infradead.org>
> Signed-off-by: Ondrej Mosnacek <omosnace(a)redhat.com>
> ---
> 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.
Oh, you're right, CONFIG_KEYS does not depend on CONFIG_MULTIUSER, for
some reason I was looking at CONFIG_SECURITY instead, which does :/ I
will need to update the commit message...
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.
I was wondering why the security/keys/permissions.c did not give the
link error and it turns out that it is due to the definition of
__kgid_val(), which is hard-coded to 0 if CINFIG_MULTIUSER=n, so the
compiler just optimizes out most of the code in key_task_permission()
(including the groups_search() call). Thus, for permissions.c it does
not matter which fallback we choose (and since this patch always
defines groups_search(), it will not lead to compile errors in
permissions.c either).
TL;DR: There is no need to fix anything in the keys code (beyond this
patch). I also checked the other functions and they are only used in
places that either depend on MULTIUSER or use also groups_alloc(),
which is already declared only when CONFIG_MULTIUSER=y.
--
paul moore
www.paul-moore.com
--
Ondrej Mosnacek <omosnace at redhat dot com>
Associate Software Engineer, Security Technologies
Red Hat, Inc.