Messages in this thread | | | Date | Sat, 6 Nov 2021 14:23:51 +0300 | Subject | Re: [PATCH] tty: vt: keyboard: do not copy an extra-byte in copy_to_user | From | Pavel Skripkin <> |
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Hi, Ajay!
On 11/6/21 12:20, Ajay Garg wrote: > 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@gmail.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);
^^^^^^^^^
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
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