Re: [PATCH] tty: vt: keyboard: do not copy an extra-byte in copy_to_user
From: Pavel Skripkin <hidden>
Date: 2021-11-06 11:24:00
Also in:
lkml
Hi, Ajay! On 11/6/21 12:20, Ajay Garg wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- 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);
^^^^^^^^^ len is reinitialized here, i.e len passed to kmalloc and len passed to copy_to_user() can be different. strlcpy() returns strlen() of source string (2nd argument), that's why we need +1 here to pass null byte to user. Am I missing something?
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;
With regards, Pavel Skripkin