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Message-ID: <435b5f7a-fcbd-f7ae-b66f-670e5997aa1b@gnuweeb.org>
Date: Wed, 11 May 2022 03:10:31 +0700
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To: cgel.zte@gmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>,
 Kees Cook <keescook@chromium.org>, Matthew Wilcox <willy@infradead.org>,
 Yang Yang <yang.yang29@zte.com.cn>, Ran Xiaokai <ran.xiaokai@zte.com.cn>,
 Yunkai Zhang <zhang.yunkai@zte.com.cn>, xu xin <xu.xin16@zte.com.cn>,
 wangyong <wang.yong12@zte.com.cn>, Linux MM Mailing List
 <linux-mm@kvack.org>,
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 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <20220507105926.d4423601230f698b0f5228d1@linux-foundation.org>
 <20220508092710.930126-1-xu.xin16@zte.com.cn>
From: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Subject: Re: [PATCH v5] mm/ksm: introduce ksm_force for each process
In-Reply-To: <20220508092710.930126-1-xu.xin16@zte.com.cn>
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On 5/8/22 4:27 PM, cgel.zte@gmail.com wrote:
> +static ssize_t ksm_force_write(struct file *file, const char __user *buf,
> +				size_t count, loff_t *ppos)
> +{
> +	struct task_struct *task;
> +	struct mm_struct *mm;
> +	char buffer[PROC_NUMBUF];
> +	int force;
> +	int err = 0;
> +
> +	memset(buffer, 0, sizeof(buffer));
> +	if (count > sizeof(buffer) - 1)
> +		count = sizeof(buffer) - 1;
> +	if (copy_from_user(buffer, buf, count)) {
> +		err = -EFAULT;
> +		goto out_return;
> +	}

This one looks like over-zeroing to me. You don't need to zero
all elements in the array. You're going to overwrite it with
`copy_from_user()` anyway.

Just zero the last potentially useful element by using @count
as the index. It can be like this:

```
	char buffer[PROC_NUMBUF];

	if (count > sizeof(buffer) - 1)
		count = sizeof(buffer) - 1;
	if (copy_from_user(buffer, buf, count))
		return -EFAULT;
	buffer[count] = '\0';
```

-- 
Ammar Faizi