Re: [PATCH] ref_tracker: use %p instead of %px in debugfs dentry name

[Jeff Layton]

On Thu, 2025-07-31 at 09:32 -0700, Kees Cook wrote:
> On Thu, Jul 31, 2025 at 07:57:05AM -0400, Jeff Layton wrote:
> > As Kees points out, this is a kernel address leak, and debugging is
> > not a sufficiently good reason to expose the real kernel address.
> > 
> > Fixes: 65b584f53611 ("ref_tracker: automatically register a file in debugfs for a ref_tracker_dir")
> > Reported-by: Kees Cook <kees@xxxxxxxxxx>
> > Closes: https://lore.kernel.org/netdev/202507301603.62E553F93@keescook/
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> 
> Probably better to use a global u64 counter, but %p can work.
> 

I disagree here, again for debugging purposes...

Other kernel debugging code can display a hashed pointer via tracepoint
or printk message, etc. Using the same value in the name here gives us
a mechanism to match that up to the correct debugfs file.

Using a counter would make that harder, and you'd have to store the
counter value in the object (or reach into the dentry -- yuck).

Plus if we _really_ need the physical addresses here in the future, we
can boot with no_hash_pointers and get them.

> Thanks for removing %px!

Thanks for pointing out the problem!
-- 
Jeff Layton <jlayton@xxxxxxxxxx>