Messages in this thread | | | Subject | Re: [PATCH v2] block: Check ADMIN before NICE for IOPRIO_CLASS_RT | From | Bart Van Assche <> | Date | Mon, 15 Nov 2021 10:40:00 -0800 |
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On 11/15/21 10:16 AM, Alistair Delva wrote: > Booting to Android userspace on 5.14 or newer triggers the following > SELinux denial: > > avc: denied { sys_nice } for comm="init" capability=23 > scontext=u:r:init:s0 tcontext=u:r:init:s0 tclass=capability > permissive=0 > > Init is PID 0 running as root, so it already has CAP_SYS_ADMIN. For > better compatibility with older SEPolicy, check ADMIN before NICE. > > Fixes: 9d3a39a5f1e4 ("block: grant IOPRIO_CLASS_RT to CAP_SYS_NICE") > Signed-off-by: Alistair Delva <adelva@google.com> > Cc: Khazhismel Kumykov <khazhy@google.com> > Cc: Bart Van Assche <bvanassche@acm.org> > Cc: Serge Hallyn <serge@hallyn.com> > Cc: Jens Axboe <axboe@kernel.dk> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: Paul Moore <paul@paul-moore.com> > Cc: selinux@vger.kernel.org > Cc: linux-security-module@vger.kernel.org > Cc: kernel-team@android.com > Cc: stable@vger.kernel.org # v5.14+ > --- > v2: added comment requested by Jens > block/ioprio.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/block/ioprio.c b/block/ioprio.c > index 0e4ff245f2bf..313c14a70bbd 100644 > --- a/block/ioprio.c > +++ b/block/ioprio.c > @@ -69,7 +69,14 @@ int ioprio_check_cap(int ioprio) > > switch (class) { > case IOPRIO_CLASS_RT: > - if (!capable(CAP_SYS_NICE) && !capable(CAP_SYS_ADMIN)) > + /* > + * Originally this only checked for CAP_SYS_ADMIN, > + * which was implicitly allowed for pid 0 by security > + * modules such as SELinux. Make sure we check > + * CAP_SYS_ADMIN first to avoid a denial/avc for > + * possibly missing CAP_SYS_NICE permission. > + */ > + if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE)) > return -EPERM; > fallthrough; > /* rt has prio field too */ >
Are there any other SELinux policies (Fedora?) that need to be verified?
Anyway:
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
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