[PATCH 4.19 11/52] sched/rt: Disallow writing invalid values to sched_rt_period_us

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.19-stable review patch.  If anyone has any objections, please let me know.

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

From: Cyril Hrubis <chrubis@suse.cz>

[ Upstream commit 079be8fc630943d9fc70a97807feb73d169ee3fc ]

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@suse.cz/

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231002115553.3007-2-chrubis@suse.cz
[ pvorel: rebased for 4.19 ]
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/sched/rt.c |    5 +----
 kernel/sysctl.c   |    5 +++++
 2 files changed, 6 insertions(+), 4 deletions(-)

--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2658,9 +2658,6 @@ 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))
 		return -EINVAL;
@@ -2690,7 +2687,7 @@ 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
@@ -127,6 +127,7 @@ static int zero;
 static int __maybe_unused one = 1;
 static int __maybe_unused two = 2;
 static int __maybe_unused four = 4;
+static int int_max = INT_MAX;
 static unsigned long zero_ul;
 static unsigned long one_ul = 1;
 static unsigned long long_max = LONG_MAX;
@@ -464,6 +465,8 @@ static struct ctl_table kern_table[] = {
 		.maxlen		= sizeof(unsigned int),
 		.mode		= 0644,
 		.proc_handler	= sched_rt_handler,
+		.extra1		= &one,
+		.extra2		= &int_max,
 	},
 	{
 		.procname	= "sched_rt_runtime_us",
@@ -471,6 +474,8 @@ static struct ctl_table kern_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= sched_rt_handler,
+		.extra1		= &neg_one,
+		.extra2		= &int_max,
 	},
 	{
 		.procname	= "sched_rr_timeslice_ms",