Re: [PATCH v5] mm/ksm: introduce ksm_force for each process

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On 5/11/22 3:30 AM, Andrew Morton wrote:
On Wed, 11 May 2022 03:10:31 +0700 Ammar Faizi <ammarfaizi2@xxxxxxxxxxx> wrote:

On 5/8/22 4:27 PM, cgel.zte@xxxxxxxxx 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';
```

Use strncpy_from_user()?

Sounds better.

Can this code use proc_dointvec_minmax() or similar?

Not familiar with that API at all. Leaving it to other participants...

--
Ammar Faizi



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