[PATCH RESEND v2 20/26] tty: sysrq: let procfs copy in writes to /proc/sysrq-trigger

[Christian Brauner <brauner@kernel.org>]

Implement ->proc_write_buf() so procfs copies in what is written before
it pins the entry, and handle the keys from that copy. Writes larger
than PAGE_SIZE - 1 bytes fail with -EINVAL now. They used to trigger the
first key, or all of them in bulk mode. procfs allocates the copy, which
is as small as the write, opening the file allocated as much already.

Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 drivers/tty/sysrq.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index f4571d05b496..99363e1b59ed 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -1200,17 +1200,14 @@ EXPORT_SYMBOL(unregister_sysrq_key);
  * However, if the first character is an underscore,
  * all characters are processed.
  */
-static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
+static ssize_t write_sysrq_trigger(struct file *file, char *buf,
 				   size_t count, loff_t *ppos)
 {
 	bool bulk = false;
 	size_t i;
 
 	for (i = 0; i < count; i++) {
-		char c;
-
-		if (get_user(c, buf + i))
-			return -EFAULT;
+		char c = buf[i];
 
 		if (c == '_')
 			bulk = true;
@@ -1225,7 +1222,7 @@ static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
 }
 
 static const struct proc_ops sysrq_trigger_proc_ops = {
-	.proc_write	= write_sysrq_trigger,
+	.proc_write_buf	= write_sysrq_trigger,
 	.proc_lseek	= noop_llseek,
 };
 

-- 
2.53.0