Re: [PATCH] [request for inclusion] Realtime LSM

Chris Wright
2005-01-14T23:12:46Z

* Matt Mackall (mpm@selenic.com) wrote:
> On Fri, Jan 14, 2005 at 12:10:21PM -0800, Chris Wright wrote:
> > The basic issue on the rlimit value is how to sanely encode nice values,
> > realtime prioroties and scheduler policies into a number. The first
> > incarnation was the clumsiest, and tried to pack it all into a number
> > in range of [0,139]. This, as many agree, too closely reflects kernel
> > internal values. This one gives 0-39 (nice values 19,-20) to RLIMIT_NICE,
> > and 0-99 (rt priorities) to RLIMIT_RTPRIO. There's no distinction in rt
> > policy, and the traditional override (CAP_SYS_NICE) is still in place.
> > The defaults for both rlimits are 0, and behaviour should be backwards
> > compatible. I tested this one a bit, and it worked as expected. I've
> > got a patch to pam_limits as well, although it's untested.
>
> This is looking pretty good.
>
> > +#define NICE_TO_RLIMIT_NICE(nice) (19 - nice)
> ...
> > +unsigned long nice_to_rlimit_nice(const int nice)
> > +{
> > + return NICE_TO_RLIMIT_NICE(nice);
> > +}
>
> This is a bit silly.

Heh, I wondered what comment that would get ;-) It's gone.

> > - if (niceval < task_nice(p) && !capable(CAP_SYS_NICE)) {
> > + if (niceval < task_nice(p) &&
> > + nice_to_rlimit_nice(niceval) >
> > + p->signal->rlim[RLIMIT_NICE].rlim_cur &&
> > + !capable(CAP_SYS_NICE)) {
>
> Perhaps we want another helper function to do the rlim and
> CAP_SYS_NICE check together.

Sure.
-chris
--

===== include/asm-i386/resource.h 1.5 vs edited =====
--- 1.5/include/asm-i386/resource.h 2004-08-23 01:15:26 -07:00
+++ edited/include/asm-i386/resource.h 2005-01-14 13:48:53 -08:00
@@ -18,8 +18,11 @@
#define RLIMIT_LOCKS 10 /* maximum file locks held */
#define RLIMIT_SIGPENDING 11 /* max number of pending signals */
#define RLIMIT_MSGQUEUE 12 /* maximum bytes in POSIX mqueues */
+#define RLIMIT_NICE 13 /* max nice prio allowed to raise to
+ 0-39 for nice level 19 .. -20 */
+#define RLIMIT_RTPRIO 14 /* maximum realtime priority */

-#define RLIM_NLIMITS 13
+#define RLIM_NLIMITS 15

/*
@@ -45,6 +48,8 @@
{ RLIM_INFINITY, RLIM_INFINITY }, \
{ MAX_SIGPENDING, MAX_SIGPENDING }, \
{ MQ_BYTES_MAX, MQ_BYTES_MAX }, \
+ { 0, 0 }, \
+ { 0, 0 }, \
}

#endif /* __KERNEL__ */
===== include/asm-x86_64/resource.h 1.5 vs edited =====
--- 1.5/include/asm-x86_64/resource.h 2004-08-23 01:15:26 -07:00
+++ edited/include/asm-x86_64/resource.h 2005-01-14 14:17:38 -08:00
@@ -18,8 +18,11 @@
#define RLIMIT_LOCKS 10 /* maximum file locks held */
#define RLIMIT_SIGPENDING 11 /* max number of pending signals */
#define RLIMIT_MSGQUEUE 12 /* maximum bytes in POSIX mqueues */
+#define RLIMIT_NICE 13 /* max nice prio allowed to raise to
+ 0-39 for nice level 19 .. -20 */
+#define RLIMIT_RTPRIO 14 /* maximum realtime priority */

-#define RLIM_NLIMITS 13
+#define RLIM_NLIMITS 15

/*
* SuS says limits have to be unsigned.
@@ -44,6 +47,8 @@
{ RLIM_INFINITY, RLIM_INFINITY }, \
{ MAX_SIGPENDING, MAX_SIGPENDING }, \
{ MQ_BYTES_MAX, MQ_BYTES_MAX }, \
+ { 0, 0 }, \
+ { 0, 0 }, \
}

#endif /* __KERNEL__ */
===== include/linux/sched.h 1.291 vs edited =====
--- 1.291/include/linux/sched.h 2005-01-11 16:42:57 -08:00
+++ edited/include/linux/sched.h 2005-01-14 13:58:32 -08:00
@@ -767,6 +767,7 @@ extern void sched_idle_next(void);
extern void set_user_nice(task_t *p, long nice);
extern int task_prio(const task_t *p);
extern int task_nice(const task_t *p);
+extern int can_nice(const task_t *p, const int nice);
extern int task_curr(const task_t *p);
extern int idle_cpu(int cpu);
extern int sched_setscheduler(struct task_struct *, int, struct sched_param *);
===== kernel/sched.c 1.407 vs edited =====
--- 1.407/kernel/sched.c 2005-01-11 16:42:35 -08:00
+++ edited/kernel/sched.c 2005-01-14 15:03:44 -08:00
@@ -3121,6 +3121,19 @@ out_unlock:

EXPORT_SYMBOL(set_user_nice);

+/**
+ * can_nice - check if a task can reduce its nice value
+ @p: task
+ * @nice: nice value
+ */
+int can_nice(const task_t *p, const int nice)
+{
+ /* convert nice value [19,-20] to rlimit style value [0,39] */
+ int nice_rlim = 19 - nice;
+ return (nice_rlim <= p->signal->rlim[RLIMIT_NICE].rlim_cur ||
+ capable(CAP_SYS_NICE));
+}
+
#ifdef __ARCH_WANT_SYS_NICE

/*
@@ -3140,12 +3153,8 @@ asmlinkage long sys_nice(int increment)
* We don't have to worry. Conceptually one call occurs first
* and we have a single winner.
*/
- if (increment < 0) {
- if (!capable(CAP_SYS_NICE))
- return -EPERM;
- if (increment < -40)
- increment = -40;
- }
+ if (increment < -40)
+ increment = -40;
if (increment > 40)
increment = 40;

@@ -3155,6 +3164,9 @@ asmlinkage long sys_nice(int increment)
if (nice > 19)
nice = 19;

+ if (increment < 0 && !can_nice(current, nice))
+ return -EPERM;
+
retval = security_task_setnice(current, nice);
if (retval)
return retval;
@@ -3252,6 +3264,7 @@ recheck:
return -EINVAL;

if ((policy == SCHED_FIFO || policy == SCHED_RR) &&
+ param->sched_priority > p->signal->rlim[RLIMIT_RTPRIO].rlim_cur &&
!capable(CAP_SYS_NICE))
return -EPERM;
if ((current->euid != p->euid) && (current->euid != p->uid) &&
===== kernel/sys.c 1.104 vs edited =====
--- 1.104/kernel/sys.c 2005-01-11 16:42:35 -08:00
+++ edited/kernel/sys.c 2005-01-14 14:10:11 -08:00
@@ -225,7 +225,7 @@ static int set_one_prio(struct task_stru
error = -EPERM;
goto out;
}
- if (niceval < task_nice(p) && !capable(CAP_SYS_NICE)) {
+ if (niceval < task_nice(p) && !can_nice(p, niceval)) {
error = -EACCES;
goto out;
}