Re: [PATCH] printf: add bad-pointer tests for %ptT and %ptS

[Petr Mladek <pmladek@suse.com>]

On Mon 2026-03-16 16:55:36, Andy Shevchenko wrote:
> On Mon, Mar 16, 2026 at 04:43:34PM +0545, Shuvam Pandey wrote:
> > The printf KUnit suite exercises valid %ptR, %ptT, and %ptS inputs,
> > but it does not cover bad pointers for the time64_t and timespec64
> > paths.
> > 
> > Add NULL and low-address pointer cases for %ptT and %ptS. The new
> > checks verify that time_and_date() rejects bad pointers before
> > dereferencing them and formats them as "(null)" or "(efault)".
> > 
> > Validated with the printf KUnit suite on arm64 QEMU and an
> > incremental W=1 build of lib/tests/printf_kunit.o.
> 
> NAK.
> 
> It has nothing to do with %pt.

Let me play the devil advocate.

There is no single check which would catch bad pointers for
the various %p? format modifiers. It is because some of them
handle them differently, for example, %pK, %pe, or plain %p.

I want to say that wrong pointers passed to %pt? are caught only
because of the explicit check in:

static noinline_for_stack
char *time_and_date(char *buf, char *end, void *ptr, struct printf_spec spec,
		    const char *fmt)
{
	if (check_pointer(&buf, end, ptr, spec))    
		return buf;
[...]
}

So, pointer-modifier-specific checks of wrong input might make sense.

Of course, it would be nice to create some generic solution for
all affected pointer modifiers and not just for "%pt?".

Best Regards,
Petr