* Re: [PATCH v2] block: Check ADMIN before NICE for IOPRIO_CLASS_RT
2021-11-15 18:16 [PATCH v2] block: Check ADMIN before NICE for IOPRIO_CLASS_RT Alistair Delva
@ 2021-11-15 18:40 ` Bart Van Assche
2021-11-15 19:26 ` Serge E. Hallyn
2021-11-15 21:37 ` Jens Axboe
2 siblings, 0 replies; 4+ messages in thread
From: Bart Van Assche @ 2021-11-15 18:40 UTC (permalink / raw)
To: Alistair Delva, linux-kernel
Cc: Khazhismel Kumykov, Serge Hallyn, Jens Axboe, Greg Kroah-Hartman,
Paul Moore, selinux, linux-security-module, kernel-team, stable
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>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v2] block: Check ADMIN before NICE for IOPRIO_CLASS_RT
2021-11-15 18:16 [PATCH v2] block: Check ADMIN before NICE for IOPRIO_CLASS_RT Alistair Delva
2021-11-15 18:40 ` Bart Van Assche
@ 2021-11-15 19:26 ` Serge E. Hallyn
2021-11-15 21:37 ` Jens Axboe
2 siblings, 0 replies; 4+ messages in thread
From: Serge E. Hallyn @ 2021-11-15 19:26 UTC (permalink / raw)
To: Alistair Delva
Cc: linux-kernel, Khazhismel Kumykov, Bart Van Assche, Serge Hallyn,
Jens Axboe, Greg Kroah-Hartman, Paul Moore, selinux,
linux-security-module, kernel-team, stable, john.johansen
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
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v2] block: Check ADMIN before NICE for IOPRIO_CLASS_RT
2021-11-15 18:16 [PATCH v2] block: Check ADMIN before NICE for IOPRIO_CLASS_RT Alistair Delva
2021-11-15 18:40 ` Bart Van Assche
2021-11-15 19:26 ` Serge E. Hallyn
@ 2021-11-15 21:37 ` Jens Axboe
2 siblings, 0 replies; 4+ messages in thread
From: Jens Axboe @ 2021-11-15 21:37 UTC (permalink / raw)
To: linux-kernel, Alistair Delva
Cc: linux-security-module, stable, Paul Moore, kernel-team, selinux,
Khazhismel Kumykov, Serge Hallyn, Greg Kroah-Hartman,
Bart Van Assche
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,
--
Jens Axboe
^ permalink raw reply [flat|nested] 4+ messages in thread