[PATCH 2/2 v4] proc: Add LSM hook checks to /proc/<tid>/timerslack_ns

From: John Stultz
Date: Thu Jul 21 2016 - 16:24:41 EST

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>
* Initial swing at adding settimerslack LSM hook
* Fix current/p switchup bug noted by NickK
* Add gettimerslack hook suggested by NickK
* Dropped adding get/settimerslack LSM hooks, and
just reuse the get/setscheduler ones.

fs/proc/base.c | 10 ++++++++++
1 file changed, 10 insertions(+)

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;
+ }
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;
seq_printf(m, "%llu\n", p->timer_slack_ns);