On Thu, Jul 21, 2016 at 4:24 PM, John Stultz <john.stultz@xxxxxxxxxx> wrote:
> As requested, this patch checks the existing LSM hooks
> task_getscheduler/task_setscheduler when reading or modifying
> the task's timerslack value.
>
> Previous versions added new get/settimerslack LSM hooks, but
> since they checked the same PROCESS__SET/GETSCHED values as
> existing hooks, it was suggested we just use the existing ones.
>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: "Serge E. Hallyn" <serge@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> CC: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
> Cc: Oren Laadan <orenl@xxxxxxxxxxx>
> Cc: Ruchi Kandoi <kandoiruchi@xxxxxxxxxx>
> Cc: Rom Lemarchand <romlem@xxxxxxxxxxx>
> Cc: Todd Kjos <tkjos@xxxxxxxxxx>
> Cc: Colin Cross <ccross@xxxxxxxxxxx>
> Cc: Nick Kralevich <nnk@xxxxxxxxxx>
> Cc: Dmitry Shmidt <dimitrysh@xxxxxxxxxx>
> Cc: Elliott Hughes <enh@xxxxxxxxxx>
> Cc: James Morris <jmorris@xxxxxxxxx>
> Cc: Android Kernel Team <kernel-team@xxxxxxxxxxx>
> Cc: linux-security-module@xxxxxxxxxxxxxxx
> Cc: selinux@xxxxxxxxxxxxx
> Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
> ---
> v2:
> * Initial swing at adding settimerslack LSM hook
> v3:
> * Fix current/p switchup bug noted by NickK
> * Add gettimerslack hook suggested by NickK
> v4:
> * Dropped adding get/settimerslack LSM hooks, and
> just reuse the get/setscheduler ones.
>
> fs/proc/base.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
For some reason I'm having a hard time finding patch 1/2 in the
patchset, but this patch looks reasonable to me. We already have some
LSM checking via the ptrace_may_access() call, but this adds some
additional granularity which could be a good thing.
Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index c94abae..02f8389 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2286,6 +2286,12 @@ static ssize_t timerslack_ns_write(struct file *file, const char __user *buf,
> goto out;
> }
>
> + err = security_task_setscheduler(p);
> + if (err) {
> + count = err;
> + goto out;
> + }
> +
> task_lock(p);
> if (slack_ns == 0)
> p->timer_slack_ns = p->default_timer_slack_ns;
> @@ -2314,6 +2320,10 @@ static int timerslack_ns_show(struct seq_file *m, void *v)
> goto out;
> }
>
> + err = security_task_getscheduler(p);
> + if (err)
> + goto out;
> +
> task_lock(p);
> seq_printf(m, "%llu\n", p->timer_slack_ns);
> task_unlock(p);
> --
> 1.9.1
>
> --
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--
paul moore
www.paul-moore.com
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