Messages in this thread Patch in this message | | | Date | Fri, 1 Sep 2023 19:45:29 +0200 | From | Petr Vorel <> | Subject | Re: [LTP] [PATCH] sched/rt: Disallow writing invalid values to sched_rt_period_us |
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> 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> > --- > kernel/sched/rt.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-)
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index 0597ba0f85ff..aed3d55de2dd 100644 > --- 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, Documentation/scheduller/sched-rt-group.rst [1] specifies this as values from -1 to (INT_MAX - 1), I guess due int range. Looking into proc_dointvec_minmax() [2] even INT_MAX would pass the check. I suppose we can do nothing about that, because there is no value in sysctl_vals[] which would represent INT_MAX - 1.
And you specify in LTP test range: from -1 to INT_MAX.
But even much shorter value than INT_MAX fails:
$ echo 1234567 > /proc/sys/kernel/sched_rt_runtime_us sh: echo: write error: Invalid argument
Ranges in /proc/sys/kernel/sched_rt_period_us works as expected.
[1] https://www.kernel.org/doc/html/latest/scheduler/sched-rt-group.html#system-wide-settings [2] https://elixir.bootlin.com/linux/latest/source/kernel/sysctl.c#L843
> }, > { > .procname = "sched_rr_timeslice_ms", > @@ -2985,9 +2989,6 @@ 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 * > @@ -3018,7 +3019,7 @@ 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();
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