linux-kernel - Re: [RFC] process /proc/PID/smaps vs /proc/PID/smaps

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Date:   Thu, 8 Sep 2022 11:42:18 +0200
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
CC:     Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>
Subject: Re: [RFC] process /proc/PID/smaps vs /proc/PID/smaps_rollup

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@axis.com/