[PATCH] SELinux: add security hook call to mediate attach_task (kernel/cpuset.c)

Add a security hook call to enable security modules to control the ability
to attach a task to a cpuset. While limited control over this operation is
possible via permission checks on the pseudo fs interface, those checks are
not sufficient to control access to the target task, which is looked up in
this function. The existing task_setscheduler hook is re-used for this
operation since this falls under the same class of operations.

Signed-off-by: David Quigley <[e-mail]>
Acked-by: Stephen Smalley <[e-mail]>
Signed-off-by: James Morris <[e-mail]>
Acked-by: Paul Jackson <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

kernel/cpuset.c

···
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
 #include <linux/seq_file.h>
+#include <linux/security.h>
 #include <linux/slab.h>
 #include <linux/smp_lock.h>
 #include <linux/spinlock.h>
···
 	cpumask_t cpus;
 	nodemask_t from, to;
 	struct mm_struct *mm;
+	int retval;
 
 	if (sscanf(pidbuf, "%d", &pid) != 1)
 		return -EIO;
···
 	} else {
 		tsk = current;
 		get_task_struct(tsk);
+	}
+
+	retval = security_task_setscheduler(tsk, 0, NULL);
+	if (retval) {
+		put_task_struct(tsk);
+		return retval;
 	}
 
 	mutex_lock(&callback_mutex);