Re: [PATCH] mm: don't clobber partially overlapping VMA with MAP_FIXED_NOREPLACE

[Jann Horn]

On Fri, Oct 12, 2018 at 12:23 PM Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:
> Jann Horn <jannh@xxxxxxxxxx> writes:
> > On Wed, Oct 10, 2018 at 7:19 PM Michal Hocko <mhocko@xxxxxxxx> 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@debian:~$ 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. :)