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

Andrew Morton
2005-03-08T07:01:28Z

Matt Mackall <mpm@selenic.com> wrote:
>
> Add a pair of rlimits for allowing non-root tasks to raise nice and rt
> priorities. Defaults to traditional behavior. Originally written by
> Chris Wright.

It needs some dinking with because Ingo has been playing games in my
resource.h. Here's the end result. Unlike yours, this will work on alpha,
mips and sparc[64], too ;)

From: Matt Mackall <mpm@selenic.com>

Add a pair of rlimits for allowing non-root tasks to raise nice and rt
priorities. Defaults to traditional behavior. Originally written by
Chris Wright.

The patch implements a simple rlimit ceiling for the RT (and nice) priorities
a task can set. The rlimit defaults to 0, meaning no change in behavior by
default. A value of 50 means RT priority levels 1-50 are allowed. A value of
100 means all 99 privilege levels from 1 to 99 are allowed. CAP_SYS_NICE is
blanket permission.

Signed-off-by: Matt Mackall <mpm@selenic.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

25-akpm/include/asm-generic/resource.h | 7 ++++++-
25-akpm/include/linux/sched.h | 1 +
25-akpm/kernel/sched.c | 25 +++++++++++++++++++------
25-akpm/kernel/sys.c | 2 +-
4 files changed, 27 insertions(+), 8 deletions(-)

diff -puN include/asm-generic/resource.h~nice-and-rt-prio-rlimits include/asm-generic/resource.h
--- 25/include/asm-generic/resource.h~nice-and-rt-prio-rlimits 2005-03-07 22:50:45.000000000 -0800
+++ 25-akpm/include/asm-generic/resource.h 2005-03-07 22:52:10.000000000 -0800
@@ -41,8 +41,11 @@
#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.
@@ -81,6 +84,8 @@
[RLIMIT_LOCKS] = { RLIM_INFINITY, RLIM_INFINITY }, \
[RLIMIT_SIGPENDING] = { 0, 0 }, \
[RLIMIT_MSGQUEUE] = { MQ_BYTES_MAX, MQ_BYTES_MAX }, \
+ [RLIMIT_NICE] = { 0, 0 }, \
+ [RLIMIT_RTPRIO] = { 0, 0 }, \
}

#endif /* __KERNEL__ */
diff -puN include/linux/sched.h~nice-and-rt-prio-rlimits include/linux/sched.h
--- 25/include/linux/sched.h~nice-and-rt-prio-rlimits 2005-03-07 22:50:45.000000000 -0800
+++ 25-akpm/include/linux/sched.h 2005-03-07 22:50:45.000000000 -0800
@@ -872,6 +872,7 @@ 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 *);
diff -puN kernel/sched.c~nice-and-rt-prio-rlimits kernel/sched.c
--- 25/kernel/sched.c~nice-and-rt-prio-rlimits 2005-03-07 22:50:45.000000000 -0800
+++ 25-akpm/kernel/sched.c 2005-03-07 22:50:45.000000000 -0800
@@ -3304,6 +3304,19 @@ struct task_struct *kgdb_get_idle(int th
}
#endif

+/*
+ * 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

/*
@@ -3323,12 +3336,8 @@ 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;

@@ -3338,6 +3347,9 @@ 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;
@@ -3453,6 +3465,7 @@ 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) &&
diff -puN kernel/sys.c~nice-and-rt-prio-rlimits kernel/sys.c
--- 25/kernel/sys.c~nice-and-rt-prio-rlimits 2005-03-07 22:50:45.000000000 -0800
+++ 25-akpm/kernel/sys.c 2005-03-07 22:50:45.000000000 -0800
@@ -229,7 +229,7 @@ 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;
}
_