[PATCH] sched/fair: Null terminate buffer when updating tunable_scaling

Mel Gorman
2021-09-27T11:46:42Z

This patch null-terminates the temporary buffer in sched_scaling_write()
so kstrtouint() does not return failure and checks the value is valid.

Before
$ cat /sys/kernel/debug/sched/tunable_scaling
1
$ echo 0 > /sys/kernel/debug/sched/tunable_scaling
-bash: echo: write error: Invalid argument
$ cat /sys/kernel/debug/sched/tunable_scaling
1

After
$ cat /sys/kernel/debug/sched/tunable_scaling
1
$ echo 0 > /sys/kernel/debug/sched/tunable_scaling
$ cat /sys/kernel/debug/sched/tunable_scaling
0
$ echo 3 > /sys/kernel/debug/sched/tunable_scaling
-bash: echo: write error: Invalid argument

Fixes: 8a99b6833c88 ("sched: Move SCHED_DEBUG sysctl to debugfs")
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
kernel/sched/debug.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 49716228efb4..17a653b67006 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -173,16 +173,22 @@ static ssize_t sched_scaling_write(struct file *filp, const char __user *ubuf,
size_t cnt, loff_t *ppos)
{
char buf[16];
+ unsigned int scaling;

if (cnt > 15)
cnt = 15;

if (copy_from_user(&buf, ubuf, cnt))
return -EFAULT;
+ buf[cnt] = '\0';

- if (kstrtouint(buf, 10, &sysctl_sched_tunable_scaling))
+ if (kstrtouint(buf, 10, &scaling))
return -EINVAL;

+ if (scaling >= SCHED_TUNABLESCALING_END)
+ return -EINVAL;
+
+ sysctl_sched_tunable_scaling = scaling;
if (sched_update_scaling())
return -EINVAL;