linux-kernel - Re: [PATCH] mm: don't clobber partially overlapping VMA with MAP_FIXED

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Date:   Fri, 12 Oct 2018 14:09:52 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Michal Hocko <mhocko@...e.com>, Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        abdhalee@...ux.vnet.ibm.com, joel@....id.au,
        Kees Cook <keescook@...omium.org>,
        Jason Evans <jasone@...gle.com>,
        David Goldblatt <davidtgoldblatt@...il.com>,
        Edward Tomasz Napierała <trasz@...ebsd.org>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Daniel Micay <danielmicay@...il.com>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: don't clobber partially overlapping VMA with MAP_FIXED_NOREPLACE

On Fri, Oct 12, 2018 at 12:23 PM Michael Ellerman <mpe@...erman.id.au> wrote:
> Jann Horn <jannh@...gle.com> writes:
> > On Wed, Oct 10, 2018 at 7:19 PM Michal Hocko <mhocko@...e.com> wrote:
> >> On Wed 10-10-18 17:27:36, Jann Horn wrote:
> >> > Daniel Micay reports that attempting to use MAP_FIXED_NOREPLACE in an
> >> > application causes that application to randomly crash. The existing check
> >> > for handling MAP_FIXED_NOREPLACE looks up the first VMA that either
> >> > overlaps or follows the requested region, and then bails out if that VMA
> >> > overlaps *the start* of the requested region. It does not bail out if the
> >> > VMA only overlaps another part of the requested region.
> >>
> >> I do not understand. Could you give me an example?
> >
> > Sure.
> >
> > =======
> > user@...ian:~$ cat mmap_fixed_simple.c
> > #include <sys/mman.h>
> > #include <errno.h>
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <unistd.h>
>
> ..
>
> Mind if I turn that into a selftest?

Feel free to do that. :)