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    Subject[PATCH 5.14 140/172] sched/fair: Null terminate buffer when updating tunable_scaling
    Date
    From: Mel Gorman <mgorman@techsingularity.net>

    [ Upstream commit 703066188f63d66cc6b9d678e5b5ef1213c5938e ]

    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>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
    Link: https://lore.kernel.org/r/20210927114635.GH3959@techsingularity.net
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 7e08e3d947c2..2c879cd02a5f 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;

    --
    2.33.0


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