linux-kernel - [PATCH] tty: vt: keyboard: do not copy an extra-byte in copy_to

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Message-Id: <20211106092041.43745-1-ajaygargnsit@gmail.com>
Date:   Sat,  6 Nov 2021 14:50:40 +0530
From:   Ajay Garg <ajaygargnsit@...il.com>
To:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Ajay Garg <ajaygargnsit@...il.com>
Subject: [PATCH] tty: vt: keyboard: do not copy an extra-byte in copy_to_user

Both (statically-allocated) "user_kdgkb->kb_string" and
(dynamically-allocated) "kbs" are of length "len", so we must
not copy more than "len" bytes.

Signed-off-by: Ajay Garg <ajaygargnsit@...il.com>
---
 drivers/tty/vt/keyboard.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index c7fbbcdcc346..dfef7de8a057 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -2070,7 +2070,7 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
 		len = strlcpy(kbs, func_table[kb_func] ? : "", len);
 		spin_unlock_irqrestore(&func_buf_lock, flags);
 
-		ret = copy_to_user(user_kdgkb->kb_string, kbs, len + 1) ?
+		ret = copy_to_user(user_kdgkb->kb_string, kbs, len) ?
 			-EFAULT : 0;
 
 		break;
-- 
2.30.2