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

Chris Wright
2005-01-07T22:31:27Z

* Christoph Hellwig (hch@infradead.org) wrote:
> On Fri, Jan 07, 2005 at 01:49:41PM -0800, Andrew Morton wrote:
> > Chris Wright <chrisw@osdl.org> wrote:
> > >
> > > ...
> > > Last I checked they could be controlled separately in that module. It
> > > has been suggested (by me and others) that one possible solution would
> > > be to expand it to be generic for all caps.
> >
> > Maybe this is the way?
>
> It's at least not as bad as the current hack (when properly done in
> the capabilities modules instead of adding one ontop).
>
> I must say I'm not exactly happy with that idea still. It ties the
> privilegues we have been separating from a special uid (0) to filesystem
> permissions again. It's not nessecarily a bad idea per, but it doesn't
> really fit into the model we've been working to. I'd expect quite a few
> unpleasant devices when a user detects that the distibution had been
> binding various capabilities to uids/gids behinds his back.

I agree, it's still a hack, just a generic and complete hack ;-)

> So to make forward progress I'd like the audio people to confirm whether
> the mlock bits in 2.6.9+ do help that half of their requirement first

It sure should, but I guess they can reply on that.

> (and if not find a way to fix it) and then tackle the scheduling part.
> For that one I really wonder whether the combination of the now actually
> working nicelevels (see Mingo's post) and a simple wrapper for the really
> high requirements cases doesn't work.

I saw Jack (I think) post some numbers showing that it wasn't enough.
What about making priority level protected via rlimit?

Here's an uncompiled, untested patch doing that (probably has some math
error or logic hole in it, but idea seems sound enough). I think it has
at least one problem, where nice 19 process, could renice itself back to
0. And it doesn't really handle the different scheduling policies,
other than implicit 40 - 139 being used for SCHED_FIFO/SCHED_RR.

It takes the 140 priority levels (0-139), inverts their priority
order, and then uses that number as the basis for the rlimit (so that a
larger rlimit means higher priority, to fall inline with normal rlimit
semantics). Defaults to 19 (which should be niceval of 0). And allows
CAP_SYS_NICE to continue to override if the rlimit is too low.

===== kernel/sched.c 1.386 vs edited =====
--- 1.386/kernel/sched.c 2005-01-04 18:48:21 -08:00
+++ edited/kernel/sched.c 2005-01-07 14:23:32 -08:00
@@ -3009,12 +3009,8 @@ 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;

@@ -3024,6 +3020,11 @@ asmlinkage long sys_nice(int increment)
if (nice > 19)
nice = 19;

+ if ((MAX_PRIO-1) - NICE_TO_PRIO(nice) >
+ current->signal->rlim[RLIMIT_PRIO].rlim_cur &&
+ !capable(CAP_SYS_NICE))
+ return -EPERM;
+
retval = security_task_setnice(current, nice);
if (retval)
return retval;
@@ -3057,6 +3058,15 @@ int task_nice(const task_t *p)
}

/**
+ * nice_to_prio - return priority of give nice value
+ * @nice: nice value
+ */
+int nice_to_prio(const int nice)
+{
+ return NICE_TO_PRIO(nice);
+}
+
+/**
* idle_cpu - is a given cpu idle currently?
* @cpu: the processor in question.
*/
@@ -3140,6 +3150,7 @@ recheck:

retval = -EPERM;
if ((policy == SCHED_FIFO || policy == SCHED_RR) &&
+ lp.sched_priority+40 > p->signal->rlim[RLIMIT_PRIO].rlim_cur &&
!capable(CAP_SYS_NICE))
goto out_unlock;
if ((current->euid != p->euid) && (current->euid != p->uid) &&
===== kernel/sys.c 1.102 vs edited =====
--- 1.102/kernel/sys.c 2005-01-06 23:25:46 -08:00
+++ edited/kernel/sys.c 2005-01-07 14:13:37 -08:00
@@ -225,7 +225,9 @@ static int set_one_prio(struct task_stru
error = -EPERM;
goto out;
}
- if (niceval < task_nice(p) && !capable(CAP_SYS_NICE)) {
+ if ((MAX_PRIO-1) - nice_to_prio(niceval) >
+ p->signal->rlim[RLIMIT_PRIO].rlim_cur &&
+ !capable(CAP_SYS_NICE)) {
error = -EACCES;
goto out;
}
===== 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 2005-01-07 13:55:37 -08:00
@@ -18,8 +18,9 @@
#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_PRIO 13 /* maximum scheduling priority */

-#define RLIM_NLIMITS 13
+#define RLIM_NLIMITS 14

/*
@@ -45,6 +46,7 @@
{ RLIM_INFINITY, RLIM_INFINITY }, \
{ MAX_SIGPENDING, MAX_SIGPENDING }, \
{ MQ_BYTES_MAX, MQ_BYTES_MAX }, \
+ { 19, 19 }, \
}

#endif /* __KERNEL__ */
===== include/linux/sched.h 1.280 vs edited =====
--- 1.280/include/linux/sched.h 2005-01-04 18:48:20 -08:00
+++ edited/include/linux/sched.h 2005-01-07 14:14:16 -08:00
@@ -760,6 +760,7 @@ 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 nice_to_prio(const int nice);
extern int task_curr(const task_t *p);
extern int idle_cpu(int cpu);