[linux-yocto] [PATCH 2/3] mm: fix new crash in unmapped_area_topdown()

[jianchuan.wang at windriver.com]

From: Hugh Dickins <hughd at google.com>

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 at vger.kernel.org
Fixes: 1be7107fbe18 ("mm: larger stack guard gap, between vmas")
Reported-by: Dave Jones <davej at codemonkey.org.uk>
Debugged-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Hugh Dickins <hughd at google.com>
Acked-by: Michal Hocko <mhocko at suse.com>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Jianchuan Wang <jianchuan.wang at windriver.com>
---
 mm/mmap.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 945ff3b..91581c6 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1814,7 +1814,8 @@ unsigned long unmapped_area(struct vm_unmapped_area_info *info)
 		/* 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 */
@@ -1917,7 +1918,8 @@ unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
 		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 */
-- 
2.8.1