Re: Printk specifiers for __user pointers

[Steven Rostedt]

On Fri, 20 Nov 2020 11:44:12 -0500
Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:

> To the VSPRINTF maintainers:
> 
> Documentation/core-api/printk-formats.rst lists a large number of format 
> specifiers for pointers of various sorts.  Yet as far as I can see, 
> there is no specifier meant for use with __user pointers.
> 
> The security implications of printing the true, unmangled value of a 
> __user pointer are minimal, since doing so does not leak any kernel 
> information.  So %px would work, but tools like checkpatch.pl don't like 
> it.
> 
> Should a new specifier be added?  If not, should we simply use %px?

There's currently no user of '%pu' (although there is a '%pus'. Perhaps we
should have a '%pux'?

I would even state that if it is used, that if makes sure that the value is
indeed a user space pointer (goes through the same checks as accessing user
space), before its printed, otherwise it shows "(fault)" or something.

-- Steve