Re: [RFC] process /proc/PID/smaps vs /proc/PID/smaps_rollup

[Vincent Whitchurch]

On Tue, Sep 29, 2020 at 11:40:18AM +0900, Sergey Senozhatsky wrote:
> On (20/09/29 11:05), Sergey Senozhatsky wrote:
> > One of our unprivileged daemon process needs process PSS info. That
> > info is usually available in /proc/PID/smaps on per-vma basis, on
> > in /proc/PID/smaps_rollup as a bunch of accumulated per-vma values.
> > The latter one is much faster and simpler to get, but, unlike smaps,
> > smaps_rollup requires PTRACE_MODE_READ, which we don't want to
> > grant to our unprivileged daemon.
> > 
> > So the question is - can we get, somehow, accumulated PSS info from
> > a non-privileged process? (Iterating through all process' smaps
> > vma-s consumes quite a bit of CPU time). This is related to another
> > question - why do smaps and smaps_rollup have different permission
> > requirements?
> 
> Hold on, seems that I misread something, /proc/PID/smaps is also
> unavailable. So the question is, then, how do we get PSS info of
> a random user-space process from an unprivileged daemon?

smaps contains a lot of sensitive information, but perhaps smaps_rollup
could be allowed without ptrace rights if the range information is
masked.  I've posted a patch here:

 https://lore.kernel.org/linux-mm/20220908093919.843346-1-vincent.whitchurch@xxxxxxxx/