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sched/rt: Disallow writing invalid values to sched_rt_period_us

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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@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 5.4 ]
Reviewed-by: Petr Vorel <pvorel@suse.cz>
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
commit d2fc4134aa
2 changed files with 5 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

4
kernel/sysctl.c
View file

@ -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",