linux-kernel - [PATCH 3.16 072/204] sched/sysctl: Check user input value of sysctl_sched_time

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Message-ID: <lsq.1514480744.731020486@decadent.org.uk>
Date:   Thu, 28 Dec 2017 17:05:44 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, ethan.kernel@...il.com,
        keescook@...omium.org, "Thomas Gleixner" <tglx@...utronix.de>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>, efault@....de,
        "Ingo Molnar" <mingo@...nel.org>,
        "James Puthukattukaran" <james.puthukattukaran@...cle.com>,
        mcgrof@...nel.org, "Ethan Zhao" <ethan.zhao@...cle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [PATCH 3.16 072/204] sched/sysctl: Check user input value of
 sysctl_sched_time_avg

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ethan Zhao <ethan.zhao@...cle.com>

commit 5ccba44ba118a5000cccc50076b0344632459779 upstream.

System will hang if user set sysctl_sched_time_avg to 0:

  [root@XXX ~]# sysctl kernel.sched_time_avg_ms=0

  Stack traceback for pid 0
  0xffff883f6406c600 0 0 1 3 R 0xffff883f6406cf50 *swapper/3
  ffff883f7ccc3ae8 0000000000000018 ffffffff810c4dd0 0000000000000000
  0000000000017800 ffff883f7ccc3d78 0000000000000003 ffff883f7ccc3bf8
  ffffffff810c4fc9 ffff883f7ccc3c08 00000000810c5043 ffff883f7ccc3c08
  Call Trace:
  <IRQ> [<ffffffff810c4dd0>] ? update_group_capacity+0x110/0x200
  [<ffffffff810c4fc9>] ? update_sd_lb_stats+0x109/0x600
  [<ffffffff810c5507>] ? find_busiest_group+0x47/0x530
  [<ffffffff810c5b84>] ? load_balance+0x194/0x900
  [<ffffffff810ad5ca>] ? update_rq_clock.part.83+0x1a/0xe0
  [<ffffffff810c6d42>] ? rebalance_domains+0x152/0x290
  [<ffffffff810c6f5c>] ? run_rebalance_domains+0xdc/0x1d0
  [<ffffffff8108a75b>] ? __do_softirq+0xfb/0x320
  [<ffffffff8108ac85>] ? irq_exit+0x125/0x130
  [<ffffffff810b3a17>] ? scheduler_ipi+0x97/0x160
  [<ffffffff81052709>] ? smp_reschedule_interrupt+0x29/0x30
  [<ffffffff8173a1be>] ? reschedule_interrupt+0x6e/0x80
   <EOI> [<ffffffff815bc83c>] ? cpuidle_enter_state+0xcc/0x230
  [<ffffffff815bc80c>] ? cpuidle_enter_state+0x9c/0x230
  [<ffffffff815bc9d7>] ? cpuidle_enter+0x17/0x20
  [<ffffffff810cd6dc>] ? cpu_startup_entry+0x38c/0x420
  [<ffffffff81053373>] ? start_secondary+0x173/0x1e0

Because divide-by-zero error happens in function:

update_group_capacity()
  update_cpu_capacity()
    scale_rt_capacity()
     {
          ...
          total = sched_avg_period() + delta;
          used = div_u64(avg, total);
          ...
     }

To fix this issue, check user input value of sysctl_sched_time_avg, keep
it unchanged when hitting invalid input, and set the minimum limit of
sysctl_sched_time_avg to 1 ms.

Reported-by: James Puthukattukaran <james.puthukattukaran@...cle.com>
Signed-off-by: Ethan Zhao <ethan.zhao@...cle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: efault@....de
Cc: ethan.kernel@...il.com
Cc: keescook@...omium.org
Cc: mcgrof@...nel.org
Link: http://lkml.kernel.org/r/1504504774-18253-1-git-send-email-ethan.zhao@oracle.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/sysctl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -342,7 +342,8 @@ static struct ctl_table kern_table[] = {
 		.data		= &sysctl_sched_time_avg,
 		.maxlen		= sizeof(unsigned int),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &one,
 	},
 	{
 		.procname	= "sched_shares_window_ns",