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

št 21. 6. 2018 o 23:17 Paul Moore <paul(a)paul-moore.com&gt; napísal(a): > On Thu, Jun 21, 2018 at 4:33 AM Ondrej Mosnacek <omosnace(a)redhat.com&gt; 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&gt; > > Signed-off-by: Ondrej Mosnacek <omosnace(a)redhat.com&gt; > > --- > > include/linux/cred.h | 16 +++++++++++----- > > 1 file changed, 11 insertions(+), 5 deletions(-) > > > > diff --git a/include/linux/cred.h b/include/linux/cred.h > > index 631286535d0f..8917768453cc 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 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 *); > > #else > > static inline void groups_free(struct group_info *group_info) > > { > > @@ -78,12 +84,12 @@ 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 0; > > Is this the right fallback value? If CONFIG_MULTIUSER is disabled, > wouldn't we always want to indicate a group match? The in_group_p() > and in_egroup_p() dummy functions would seem to indicate that is the > correct behavior ... Hm, indeed this is a bit tricky and I'm guilty of not noticing this... The way I see it (now that I though about it a little), there are basically two possible semantics of groups_search(): 1. as an (auxiliary) permissions checking function (like in_[e]group_p()) -- in this case we would expect the same return value as in_group_p(), i.e. 1. 2. as a function that simply checks if a group is contained in a list of groups (taken from a cred struct) -- in this case we would expect it to return 0 in single-user mode, since there will be always no supplemental groups set for any task (if I understand it right). I guess no matter which semantic we pick, we might confuse someone expecting the other one, so I would suggest dropping this patch (or at least the fallbacks for groups_search) and explicitly handle the single-user case in audit. We should probably default to 1 in audit anyway, because the original code used in_[e]group_p(). Even though 0 would seem more logical to me, comparing GIDs doesn't really make sense in single-user mode anyway, so keeping the legacy behavior will be safer. (In fact now that I think of it, having audit enabled (or even compiled) in single-user mode does not make much sense either... maybe we should just make CONFIG_AUDIT depend on CONFIG_MULTIUSER...).