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From 880bd724f76f26f712968fdf4917174b16540a4d Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hughd@google.com>
Date: Tue, 20 Jun 2017 02:10:44 -0700
Subject: [PATCH 2/3] [SEC][Backport] mm: fix new crash in
unmapped_area_topdown()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
commit f4cb767d76cf7ee72f97dd76f6cfa6c76a5edc89 upstream.
Trinity gets kernel BUG at mm/mmap.c:1963! in about 3 minutes of
mmap testing. That's the VM_BUG_ON(gap_end < gap_start) at the
end of unmapped_area_topdown(). Linus points out how MAP_FIXED
(which does not have to respect our stack guard gap intentions)
could result in gap_end below gap_start there. Fix that, and
the similar case in its alternative, unmapped_area().
Cc: stable@vger.kernel.org
Fixes: 1be7107fbe18 ("mm: larger stack guard gap, between vmas")
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Debugged-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Jan-Simon Möller <jsmoeller@linuxfoundation.org>
---
mm/mmap.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index cbdac38..4a113e3 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1700,7 +1700,8 @@ check_current:
/* Check if current node has a suitable gap */
if (gap_start > high_limit)
return -ENOMEM;
- if (gap_end >= low_limit && gap_end - gap_start >= length)
+ if (gap_end >= low_limit &&
+ gap_end > gap_start && gap_end - gap_start >= length)
goto found;
/* Visit right subtree if it looks promising */
@@ -1803,7 +1804,8 @@ check_current:
gap_end = vm_start_gap(vma);
if (gap_end < low_limit)
return -ENOMEM;
- if (gap_start <= high_limit && gap_end - gap_start >= length)
+ if (gap_start <= high_limit &&
+ gap_end > gap_start && gap_end - gap_start >= length)
goto found;
/* Visit left subtree if it looks promising */
--
2.1.4
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