linux-kernel - Re: [PATCH v1 0/7] Remove in-tree usage of MAP

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Message-ID: <YRckSj32tCO3nPYI@zeniv-ca.linux.org.uk>
Date:   Sat, 14 Aug 2021 02:02:50 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        David Laight <David.Laight@...lab.com>,
        David Hildenbrand <david@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
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        Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE

On Sat, Aug 14, 2021 at 01:57:31AM +0000, Al Viro wrote:
> On Fri, Aug 13, 2021 at 02:58:57PM -1000, Linus Torvalds wrote:
> > On Fri, Aug 13, 2021 at 2:54 PM Linus Torvalds
> > <torvalds@...ux-foundation.org> wrote:
> > >
> > > And nobody really complained when we weakened it, so maybe removing it
> > > entirely might be acceptable.
> > 
> > I guess we could just try it and see... Worst comes to worst, we'll
> > have to put it back, but at least we'd know what crazy thing still
> > wants it..
> 
> Umm...  I'll need to go back and look through the thread, but I'm
> fairly sure that there used to be suckers that did replacement of
> binary that way (try to write, count on exclusion with execve while
> it's being written to) instead of using rename.  Install scripts
> of weird crap and stuff like that...

... and before anyone goes off - I certainly agree that using that
behaviour is not a good idea and had never been one.  All I'm saying
is that there at least used to be very random (and rarely exercised)
bits of userland relying upon that behaviour.