[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 <jmorris@namei.org>
Acked-by:  Stephen Smalley <sds@tycho.nsa.gov>
Cc: Jan Engelhardt <jengelh@linux01.gwdg.de>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/ioprio.c

@@ -24,15 +24,21 @@
 #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);
 
 	task->ioprio = ioprio;