On Mon, Nov 15, 2021 at 06:16:55PM +0000, 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
This won't harm anything, so
Acked-by: Serge Hallyn serge@hallyn.com
but questions below.
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
What do you mean, implicitly allowed for pid 0? Can you point to where that happens?
* 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;
But whichever one comes first can cause an avc denial message. It seems like we need a new capable() primitive which supports multiple bits, when more than one can authorize an action, and which emits an audit message only if all bits are missing.
fallthrough; /* rt has prio field too */-- 2.34.0.rc1.387.gb447b232ab-goog