| Message ID | 20211115181655.3608659-1-adelva@google.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Paul Moore |
| Headers | show |
| Series | [v2] block: Check ADMIN before NICE for IOPRIO_CLASS_RT | expand |
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
On Mon, 15 Nov 2021 18:16:55 +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 > > [...] Applied, thanks! [1/1] block: Check ADMIN before NICE for IOPRIO_CLASS_RT commit: 94c4b4fd25e6c3763941bdec3ad54f2204afa992 Best regards,
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 */
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(-)