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

On 11/10/21 08:22, Jiri Slaby wrote:

I don't quite understand what the problem is. Provided I wrote the code,
is there something wrong with this commit (and its explanation), in
particular?

commit 6ca03f90527e499dd5e32d6522909e2ad390896b
Author: Jiri Slaby [off-list ref]
Date:   Mon Oct 19 10:55:16 2020 +0200

      vt: keyboard, simplify vt_kdgkbsent

      Use 'strlen' of the string, add one for NUL terminator and simply do
      'copy_to_user' instead of the explicit 'for' loop. This makes the
      KDGKBSENT case more compact.

      The only thing we need to take care about is NULL 'func_table[i]'. Use
      an empty string in that case.

      The original check for overflow could never trigger as the func_buf
      strings are always shorter or equal to 'struct kbsentry's.

thanks,

As I said in my few previous emails, I don't see any bugs/problems in 
current code.

Ajay wants to be safe and he thinks, that relying on fact, that 
strlen(func_table[kb_func]) < sizeof(user_kdgkb->kb_string) is not good 
approach, since it's external for vt_do_kdgkb_ioctl. (I hope, I've 
explained his idea in the right way)



With regards,
Pavel Skripkin