Commit f4cb767d authored Jun 20, 2017 by Hugh Dickins Committed by Linus Torvalds Jun 21, 2017

mm: fix new crash in unmapped_area_topdown()



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: 1be7107f ("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>

parent 9705596d

mm/mmap.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -1817,7 +1817,8 @@ 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 */
		@@ -1920,7 +1921,8 @@ 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 */

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