Re: [PATCH] tty: vt: keyboard: do not copy an extra-byte in copy_to_user

On 11/6/21 23:44, Ajay Garg wrote:

quoted

quoted

That's the whole point of the discussion :)

The method "vt_do_kdgkb_ioctl" does not manage "func_table[kb_func]".
Thus, the method does not know whether or not
strlen(func_table[kb_func]) < sizeof(user_kdgkb->kb_string).

It manages. The code under `case KDSKBSENT:` sets func_table[] entries
via vt_kdskbsent().

kbs = strndup_user(..., sizeof(user_kdgkb->kb_string));

is used to allocate buffer for the func_table[] entry. That's my main
point :)

func_table is set in vt_kdskbent, which itself is external.

More importantly, vt_kdskbent is handled in case KDSKBSENT:, while the
strlcpy issue we are dealing with is in case KDGKBSENT:
In case KDGKBSENT, following are managed :

                 ssize_t len = sizeof(user_kdgkb->kb_string);
                 kbs = kmalloc(len, GFP_KERNEL);

while func_table[kb_func] is external entity here, so no assumption
ought to be made for it, just my 2 cents though :)

Anyhow, really, it is the maintainers' choice now :), since there
isn't a burning (compilation/runtime) issue.

I fully agree here, it's maintainer's choice. Let's sit down and wait 
what experienced people thing about this :)

I've just wanted to explain my idea better to exclude possible 
misunderstanding.

Thanks



With regards,
Pavel Skripkin