Patch "sched/rt: Disallow writing invalid values to sched_rt_period_us" has been added to the 5.4-stable tree

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This is a note to let you know that I've just added the patch titled

    sched/rt: Disallow writing invalid values to sched_rt_period_us

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     sched-rt-disallow-writing-invalid-values-to-sched_rt_period_us.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 079be8fc630943d9fc70a97807feb73d169ee3fc Mon Sep 17 00:00:00 2001
From: Cyril Hrubis <chrubis@xxxxxxx>
Date: Mon, 2 Oct 2023 13:55:51 +0200
Subject: sched/rt: Disallow writing invalid values to sched_rt_period_us

From: Cyril Hrubis <chrubis@xxxxxxx>

commit 079be8fc630943d9fc70a97807feb73d169ee3fc upstream.

The validation of the value written to sched_rt_period_us was broken
because:

  - the sysclt_sched_rt_period is declared as unsigned int
  - parsed by proc_do_intvec()
  - the range is asserted after the value parsed by proc_do_intvec()

Because of this negative values written to the file were written into a
unsigned integer that were later on interpreted as large positive
integers which did passed the check:

  if (sysclt_sched_rt_period <= 0)
	return EINVAL;

This commit fixes the parsing by setting explicit range for both
perid_us and runtime_us into the sched_rt_sysctls table and processes
the values with proc_dointvec_minmax() instead.

Alternatively if we wanted to use full range of unsigned int for the
period value we would have to split the proc_handler and use
proc_douintvec() for it however even the
Documentation/scheduller/sched-rt-group.rst describes the range as 1 to
INT_MAX.

As far as I can tell the only problem this causes is that the sysctl
file allows writing negative values which when read back may confuse
userspace.

There is also a LTP test being submitted for these sysctl files at:

  http://patchwork.ozlabs.org/project/ltp/patch/20230901144433.2526-1-chrubis@xxxxxxx/

Signed-off-by: Cyril Hrubis <chrubis@xxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231002115553.3007-2-chrubis@xxxxxxx
[ pvorel: rebased for 5.4 ]
Reviewed-by: Petr Vorel <pvorel@xxxxxxx>
Signed-off-by: Petr Vorel <pvorel@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/sched/rt.c |    5 +----
 kernel/sysctl.c   |    4 ++++
 2 files changed, 5 insertions(+), 4 deletions(-)

--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2659,9 +2659,6 @@ static int sched_rt_global_constraints(v
 
 static int sched_rt_global_validate(void)
 {
-	if (sysctl_sched_rt_period <= 0)
-		return -EINVAL;
-
 	if ((sysctl_sched_rt_runtime != RUNTIME_INF) &&
 		((sysctl_sched_rt_runtime > sysctl_sched_rt_period) ||
 		 ((u64)sysctl_sched_rt_runtime *
@@ -2693,7 +2690,7 @@ int sched_rt_handler(struct ctl_table *t
 	old_period = sysctl_sched_rt_period;
 	old_runtime = sysctl_sched_rt_runtime;
 
-	ret = proc_dointvec(table, write, buffer, lenp, ppos);
+	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 
 	if (!ret && write) {
 		ret = sched_rt_global_validate();
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -465,6 +465,8 @@ static struct ctl_table kern_table[] = {
 		.maxlen		= sizeof(unsigned int),
 		.mode		= 0644,
 		.proc_handler	= sched_rt_handler,
+		.extra1		= SYSCTL_ONE,
+		.extra2		= SYSCTL_INT_MAX,
 	},
 	{
 		.procname	= "sched_rt_runtime_us",
@@ -472,6 +474,8 @@ static struct ctl_table kern_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= sched_rt_handler,
+		.extra1		= &neg_one,
+		.extra2		= SYSCTL_INT_MAX,
 	},
 	{
 		.procname	= "sched_rr_timeslice_ms",


Patches currently in stable-queue which might be from chrubis@xxxxxxx are

queue-5.4/sched-rt-disallow-writing-invalid-values-to-sched_rt_period_us.patch
queue-5.4/sched-rt-fix-sysctl_sched_rr_timeslice-intial-value.patch
queue-5.4/sched-rt-sysctl_sched_rr_timeslice-show-default-timeslice-after-reset.patch




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