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Commit f4cb767d authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

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: default avatarDave Jones <davej@codemonkey.org.uk>
Debugged-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 9705596d

mm/mmap.c

+4 −2
Original line number Diff line number Diff line
@@ -1817,7 +1817,8 @@ 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 */
@@ -1920,7 +1921,8 @@ 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 */