Commit 28ebf895 authored by Hugh Dickins's avatar Hugh Dickins Committed by Willy Tarreau

mm: fix new crash in unmapped_area_topdown()

commit f4cb767d 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: 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>
Signed-off-by: default avatarWilly Tarreau <w@1wt.eu>
parent 1ad9a25d
......@@ -1700,7 +1700,8 @@ 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 */
......@@ -1803,7 +1804,8 @@ 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 */
......
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