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Date:   Thu, 5 Sep 2019 20:35:32 +0200
From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Aleksa Sarai <cyphar@cyphar.com>, Jeff Layton <jlayton@kernel.org>,
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        Shuah Khan <skhan@linuxfoundation.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Christian Brauner <christian@brauner.io>,
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Subject: Re: [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user
 helpers
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On Thu, Sep 05, 2019 at 07:28:01PM +0100, Al Viro wrote:
> On Thu, Sep 05, 2019 at 08:23:03PM +0200, Christian Brauner wrote:
> 
> > Because every caller of that function right now has that limit set
> > anyway iirc. So we can either remove it from here and place it back for
> > the individual callers or leave it in the helper.
> > Also, I'm really asking, why not? Is it unreasonable to have an upper
> > bound on the size (for a long time probably) or are you disagreeing with
> > PAGE_SIZE being used? PAGE_SIZE limit is currently used by sched, perf,
> > bpf, and clone3 and in a few other places.
> 
> For a primitive that can be safely used with any size (OK, any within
> the usual 2Gb limit)?  Why push the random policy into the place where
> it doesn't belong?

Ah, the "not in the helper part" makes sense.
As long as leave the check for the callers themselves.

> 
> Seriously, what's the point?  If they want to have a large chunk of
> userland memory zeroed or checked for non-zeroes - why would that
> be a problem?