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Date:   Mon, 27 Sep 2021 12:46:35 +0100
From:   Mel Gorman <mgorman@techsingularity.net>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Mike Galbraith <efault@gmx.de>, Ingo Molnar <mingo@kernel.org>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: [PATCH] sched/fair: Null terminate buffer when updating
 tunable_scaling
Message-ID: <20210927114635.GH3959@techsingularity.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-15
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User-Agent: Mutt/1.10.1 (2018-07-13)
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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;