[PATCH RFC 13/22] x86/mtrr: let procfs copy in writes to /proc/mtrr

[Christian Brauner]

Implement ->proc_write_buf() so procfs copies in what is written before
it pins the entry, and parse the command from that copy. Writes larger
than PAGE_SIZE - 1 bytes fail with -EINVAL now.

Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 arch/x86/kernel/cpu/mtrr/if.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/mtrr/if.c b/arch/x86/kernel/cpu/mtrr/if.c
index 9510e01d5103..038e2dc38797 100644
--- a/arch/x86/kernel/cpu/mtrr/if.c
+++ b/arch/x86/kernel/cpu/mtrr/if.c
@@ -91,7 +91,7 @@ mtrr_file_del(unsigned long base, unsigned long size,
  *    "base=%Lx size=%Lx type=%s" or "disable=%d"
  */
 static ssize_t
-mtrr_write(struct file *file, const char __user *buf, size_t len, loff_t * ppos)
+mtrr_write(struct file *file, char *buf, size_t len, loff_t * ppos)
 {
 	int i, err;
 	unsigned long reg;
@@ -103,9 +103,8 @@ mtrr_write(struct file *file, const char __user *buf, size_t len, loff_t * ppos)
 	memset(line, 0, LINE_SIZE);
 
 	len = min_t(size_t, len, LINE_SIZE - 1);
-	length = strncpy_from_user(line, buf, len);
-	if (length < 0)
-		return length;
+	length = strnlen(buf, len);
+	memcpy(line, buf, length);
 
 	ptr = line + length - 1;
 	if (length && *ptr == '\n')
@@ -397,7 +396,7 @@ static int mtrr_open(struct inode *inode, struct file *file)
 static const struct proc_ops mtrr_proc_ops = {
 	.proc_show		= mtrr_seq_show,
 	.proc_open		= mtrr_open,
-	.proc_write		= mtrr_write,
+	.proc_write_buf		= mtrr_write,
 	.proc_ioctl		= mtrr_ioctl,
 #ifdef CONFIG_COMPAT
 	.proc_compat_ioctl	= mtrr_ioctl,

-- 
2.53.0