sched/rt: Disallow writing invalid values to sched_rt_period_us

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

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3b627ab586fb8dbc41cd5072306070458211ea11..88fc98601413ac16dcab1c0ae4192f950cd67edb 100644 (file)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -37,6 +37,8 @@ static struct ctl_table sched_rt_sysctls[] = {
                .maxlen         = sizeof(unsigned int),
                .mode           = 0644,
                .proc_handler   = sched_rt_handler,
+               .extra1         = SYSCTL_ONE,
+               .extra2         = SYSCTL_INT_MAX,
        },
        {
                .procname       = "sched_rt_runtime_us",
@@ -44,6 +46,8 @@ static struct ctl_table sched_rt_sysctls[] = {
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = sched_rt_handler,
+               .extra1         = SYSCTL_NEG_ONE,
+               .extra2         = SYSCTL_INT_MAX,
        },
        {
                .procname       = "sched_rr_timeslice_ms",
@@ -2935,9 +2939,6 @@ static int sched_rt_global_constraints(void)
 #ifdef CONFIG_SYSCTL
 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 *
@@ -2968,7 +2969,7 @@ static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
        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();