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sched/rt: Disallow writing invalid values to sched_rt_period_us

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commit 079be8fc63 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@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
Cc: Mahmoud Adam <mngyadam@amazon.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Cyril Hrubis 2023-10-02 13:55:51 +02:00 committed by Greg Kroah-Hartman
parent d8a27ea2c9
commit 74fd1b8c44
1 changed files with 5 additions and 4 deletions
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9
kernel/sched/rt.c
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@ -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",
@ -2989,9 +2993,6 @@ 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 *
@ -3022,7 +3023,7 @@ 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();