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[Bug 1045340] regression: java segfaults on latest kernels caused by the stack gap fix
  • From: bugzilla_noreply@xxxxxxxxxx
  • Date: Thu, 22 Jun 2017 16:06:11 +0000
  • Message-id: <bug-1045340-21960-NknygH4zYz@http.bugzilla.suse.com/>
http://bugzilla.suse.com/show_bug.cgi?id=1045340
http://bugzilla.suse.com/show_bug.cgi?id=1045340#c24

--- Comment #24 from Michal Hocko <mhocko@xxxxxxxx> ---
(In reply to Marcus Meissner from comment #22)
Created attachment 729855 [details]
sk.c

From: Solar Designer <solar@xxxxxxxxxxxx>

Dear Alexander,
probably it is already known,
otherwise please share it in oss-security@
I've noticed the problem on Red Hat kernels first, and reported to Red Hat
already,
but now I've found the same problem on Ubuntu kernels.
It does not affect mainline patch "mm: larger stack guard gap, between vmas"
but seems distributors have used some other incorrect patch (shared in
linux-distros@ ??? )

Description of problem:
mmap(MAP_GROUWSDOWN) works incorrectly on Red Hat and Ubuntu kernels with
stackguard fix.

We have application that creates stack by using MAP_GROUWSDOWN , provide
this area into clone(),
where it fails on access to mapped area.

This is a different problem unrelated to this bug. In fact I would argue that
we have never supported/implemented MAP_GROUWSDOWN correctly. There is only one
stack that can work reliably because we place it above any mmaps or grow mmaps
from lower addresses. A larger gap just makes it more obvious.

Feel free to open a separate bug for this but I would tend to close it as
WONTFIX.

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