Replace kmalloc() followed by copy_from_user() with memdup_user() to
simplify and improve stm_char_write().

Allocate and copy only 'count' bytes instead of 'count + 1' since the
extra byte is unused.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 drivers/hwtracing/stm/core.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index 37584e786bb5..49791024bb86 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c

@@ -645,15 +645,9 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
 			return err;
 	}
 
-	kbuf = kmalloc(count + 1, GFP_KERNEL);
-	if (!kbuf)
-		return -ENOMEM;
-
-	err = copy_from_user(kbuf, buf, count);
-	if (err) {
-		kfree(kbuf);
-		return -EFAULT;
-	}
+	kbuf = memdup_user(buf, count);
+	if (IS_ERR(kbuf))
+		return PTR_ERR(kbuf);
 
 	pm_runtime_get_sync(&stm->dev);