Re: [PATCH 17/20] vt: Manual replacement of the deprecated strlcpy() with return values

Jiri Slaby
2021-02-26T09:49:25Z

On 22. 02. 21, 16:12, Romain Perier wrote:
> The strlcpy() reads the entire source buffer first, it is dangerous if
> the source buffer lenght is unbounded or possibility non NULL-terminated.

"length" and it's NUL, not NULL in this case.

> It can lead to linear read overflows, crashes, etc...
>
> As recommended in the deprecated interfaces [1], it should be replaced
> by strscpy.
>
> This commit replaces all calls to strlcpy that handle the return values

s/that/which/ ?
"handles"
"value"

> by the corresponding strscpy calls with new handling of the return
> values (as it is quite different between the two functions).

Sorry, I have hard times understand the whole sentence. Could you
rephrase a bit?

> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
>
> Signed-off-by: Romain Perier <romain.perier@gmail.com>
> ---
> drivers/tty/vt/keyboard.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
> index 77638629c562..5e20c6c307e0 100644
> --- a/drivers/tty/vt/keyboard.c
> +++ b/drivers/tty/vt/keyboard.c
> @@ -2067,9 +2067,12 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
> return -ENOMEM;
>
> spin_lock_irqsave(&func_buf_lock, flags);
> - len = strlcpy(kbs, func_table[kb_func] ? : "", len);
> + len = strscpy(kbs, func_table[kb_func] ? : "", len);

func_table[kb_func] is NUL-terminated and kbs is of length len anyway,
so this is only cosmetical.

> spin_unlock_irqrestore(&func_buf_lock, flags);
>
> + if (len == -E2BIG)
> + return -E2BIG;
> +

This can never happen, right?

> ret = copy_to_user(user_kdgkb->kb_string, kbs, len + 1) ?
> -EFAULT : 0;
>
>

thanks,
--
js