Re: [PATCH v4 12/20] vsprintf: add new `%pA` format specifier

[Petr Mladek <pmladek@suse.com>]

On Mon 2022-02-14 13:12:24, Miguel Ojeda wrote:
> On Mon, Feb 14, 2022 at 11:52 AM Rasmus Villemoes
> <linux@rasmusvillemoes.dk> wrote:
> >
> > I think the point is for vsnprintf() to call (back) into Rust code.
> 
> Indeed, this is the case.
> 
> > That said, I don't like the !CONFIG_RUST version to return NULL, that
> > will surely crash moments later.
> >
> > So I prefer something like
> >
> > [rust.h]
> > // no CONFIG_RUST conditional
> > +char *rust_fmt_argument(char* buf, char* end, void *ptr);
> >
> > [vsprintf.c]
> > +       case 'A':
> > +               if (IS_ENABLED(CONFIG_RUST))
> > +                   return rust_fmt_argument(buf, end, ptr);
> > +               else
> > +                   return string_nocheck(buf, end, "[%pA in non-Rust
> > code?!]", default_str_spec);

Any long message might cause buffer overflow when the caller expects
fixed short string.

> Sounds good. Or perhaps simply `break` and let it print the pointer
> (to be consistent with `g` case and non-error `e` case).

Also this might cause buffer overflow.

The most safe solution would be to use WARN_ONCE(). The only drawback
is that it might cause panic() when using "panic_on_warn" kernel
parameter. But it will not open security hole.

Best Regards,
Petr