[PATCH] lsm: add task_setioprio hook

Implement an LSM hook for setting a task's IO priority, similar to the hook
for setting a tasks's nice value.

A previous version of this LSM hook was included in an older version of
multiadm by Jan Engelhardt, although I don't recall it being submitted
upstream.

Also included is the corresponding SELinux hook, which re-uses the setsched
permission in the proccess class.

Signed-off-by: James Morris <[e-mail]>
Acked-by: Stephen Smalley <[e-mail]>
Cc: Jan Engelhardt <[e-mail]>
Cc: Chris Wright <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/ioprio.c

···
 #include <linux/blkdev.h>
 #include <linux/capability.h>
 #include <linux/syscalls.h>
+#include <linux/security.h>
 
 static int set_task_ioprio(struct task_struct *task, int ioprio)
 {
+	int err;
 	struct io_context *ioc;
 
 	if (task->uid != current->euid &&
 	    task->uid != current->uid && !capable(CAP_SYS_NICE))
 		return -EPERM;
+
+	err = security_task_setioprio(task, ioprio);
+	if (err)
+		return err;
 
 	task_lock(task);
 

include/linux/security.h

···
  *	@p contains the task_struct of process.
  *	@nice contains the new nice value.
  *	Return 0 if permission is granted.
+ * @task_setioprio
+ *	Check permission before setting the ioprio value of @p to @ioprio.
+ *	@p contains the task_struct of process.
+ *	@ioprio contains the new ioprio value
+ *	Return 0 if permission is granted.
  * @task_setrlimit:
  *	Check permission before setting the resource limits of the current
  *	process for @resource to @new_rlim.  The old resource limit values can
···
 	int (*task_getsid) (struct task_struct * p);
 	int (*task_setgroups) (struct group_info *group_info);
 	int (*task_setnice) (struct task_struct * p, int nice);
+	int (*task_setioprio) (struct task_struct * p, int ioprio);
 	int (*task_setrlimit) (unsigned int resource, struct rlimit * new_rlim);
 	int (*task_setscheduler) (struct task_struct * p, int policy,
 				  struct sched_param * lp);
···
 static inline int security_task_setnice (struct task_struct *p, int nice)
 {
 	return security_ops->task_setnice (p, nice);
+}
+
+static inline int security_task_setioprio (struct task_struct *p, int ioprio)
+{
+	return security_ops->task_setioprio (p, ioprio);
 }
 
 static inline int security_task_setrlimit (unsigned int resource,
···
 }
 
 static inline int security_task_setnice (struct task_struct *p, int nice)
+{
+	return 0;
+}
+
+static inline int security_task_setioprio (struct task_struct *p, int ioprio)
 {
 	return 0;
 }

security/dummy.c

···
 	return 0;
 }
 
+static int dummy_task_setioprio (struct task_struct *p, int ioprio)
+{
+	return 0;
+}
+
 static int dummy_task_setrlimit (unsigned int resource, struct rlimit *new_rlim)
 {
 	return 0;
···
 	set_to_dummy_if_null(ops, task_getsid);
 	set_to_dummy_if_null(ops, task_setgroups);
 	set_to_dummy_if_null(ops, task_setnice);
+	set_to_dummy_if_null(ops, task_setioprio);
 	set_to_dummy_if_null(ops, task_setrlimit);
 	set_to_dummy_if_null(ops, task_setscheduler);
 	set_to_dummy_if_null(ops, task_getscheduler);

security/selinux/hooks.c

···
 	return task_has_perm(current,p, PROCESS__SETSCHED);
 }
 
+static int selinux_task_setioprio(struct task_struct *p, int ioprio)
+{
+	return task_has_perm(current, p, PROCESS__SETSCHED);
+}
+
 static int selinux_task_setrlimit(unsigned int resource, struct rlimit *new_rlim)
 {
 	struct rlimit *old_rlim = current->signal->rlim + resource;
···
 	.task_getsid =		        selinux_task_getsid,
 	.task_setgroups =		selinux_task_setgroups,
 	.task_setnice =			selinux_task_setnice,
+	.task_setioprio =		selinux_task_setioprio,
 	.task_setrlimit =		selinux_task_setrlimit,
 	.task_setscheduler =		selinux_task_setscheduler,
 	.task_getscheduler =		selinux_task_getscheduler,