mm-fix-new-crash-in-unmapped_area_topdown.patch

   1 From f4cb767d76cf7ee72f97dd76f6cfa6c76a5edc89 Mon Sep 17 00:00:00 2001
   2 From: Hugh Dickins <hughd@google.com>
   3 Date: Tue, 20 Jun 2017 02:10:44 -0700
   4 Subject: [PATCH] mm: fix new crash in unmapped_area_topdown()
   5 MIME-Version: 1.0
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   8
   9 Trinity gets kernel BUG at mm/mmap.c:1963! in about 3 minutes of
  10 mmap testing.  That's the VM_BUG_ON(gap_end < gap_start) at the
  11 end of unmapped_area_topdown().  Linus points out how MAP_FIXED
  12 (which does not have to respect our stack guard gap intentions)
  13 could result in gap_end below gap_start there.  Fix that, and
  14 the similar case in its alternative, unmapped_area().
  15
  16 Cc: stable@vger.kernel.org
  17 Fixes: 1be7107fbe18 ("mm: larger stack guard gap, between vmas")
  18 Reported-by: Dave Jones <davej@codemonkey.org.uk>
  19 Debugged-by: Linus Torvalds <torvalds@linux-foundation.org>
  20 Signed-off-by: Hugh Dickins <hughd@google.com>
  21 Acked-by: Michal Hocko <mhocko@suse.com>
  22 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  23 Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
  24 ---
  25  mm/mmap.c | 6 ++++--
  26  1 file changed, 4 insertions(+), 2 deletions(-)
  27
  28 diff --git a/mm/mmap.c b/mm/mmap.c
  29 index 8e07976d5e47..290b77d9a01e 100644
  30 --- a/mm/mmap.c
  31 +++ b/mm/mmap.c
  32 @@ -1817,7 +1817,8 @@ unsigned long unmapped_area(struct vm_unmapped_area_info *info)
  33                 /* Check if current node has a suitable gap */
  34                 if (gap_start > high_limit)
  35                         return -ENOMEM;
  36 -               if (gap_end >= low_limit && gap_end - gap_start >= length)
  37 +               if (gap_end >= low_limit &&
  38 +                   gap_end > gap_start && gap_end - gap_start >= length)
  39                         goto found;
  40
  41                 /* Visit right subtree if it looks promising */
  42 @@ -1920,7 +1921,8 @@ unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
  43                 gap_end = vm_start_gap(vma);
  44                 if (gap_end < low_limit)
  45                         return -ENOMEM;
  46 -               if (gap_start <= high_limit && gap_end - gap_start >= length)
  47 +               if (gap_start <= high_limit &&
  48 +                   gap_end > gap_start && gap_end - gap_start >= length)
  49                         goto found;
  50
  51                 /* Visit left subtree if it looks promising */
  52 --
  53 2.11.0
  54