[PATCH RFC 14/27] profiling: let procfs copy in writes to /proc/profile

[Christian Brauner]

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

Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 kernel/profile.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/profile.c b/kernel/profile.c
index e7defa90a34c..6e4b34f35e3b 100644
--- a/kernel/profile.c
+++ b/kernel/profile.c
@@ -189,16 +189,14 @@ int __weak setup_profiling_timer(unsigned mult)
  * Writing a 'profiling multiplier' value into it also re-sets the profiling
  * interrupt frequency, on architectures that support this.
  */
-static ssize_t write_profile(struct file *file, const char __user *buf,
-			     size_t count, loff_t *ppos)
+static ssize_t write_profile(struct file *file, char *buf, size_t count,
+			     loff_t *ppos)
 {
 #ifdef CONFIG_SMP
 	if (count == sizeof(int)) {
 		unsigned int multiplier;
 
-		if (copy_from_user(&multiplier, buf, sizeof(int)))
-			return -EFAULT;
-
+		memcpy(&multiplier, buf, sizeof(int));
 		if (setup_profiling_timer(multiplier))
 			return -EINVAL;
 	}
@@ -209,7 +207,7 @@ static ssize_t write_profile(struct file *file, const char __user *buf,
 
 static const struct proc_ops profile_proc_ops = {
 	.proc_read	= read_profile,
-	.proc_write	= write_profile,
+	.proc_write_buf	= write_profile,
 	.proc_lseek	= default_llseek,
 };
 

-- 
2.53.0