From: Hugh Dickins Date: Tue, 20 Jun 2017 09:10:44 +0000 (-0700) Subject: mm: fix new crash in unmapped_area_topdown() X-Git-Tag: release-20171130_firefly~4^2~100^2~1^2~1^2~28 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=1f2284fac2180d7a9442c796d9755e3ce7ab0bd9;p=firefly-linux-kernel-4.4.55.git mm: fix new crash in unmapped_area_topdown() 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(). Fixes: 1be7107fbe18 ("mm: larger stack guard gap, between vmas") Reported-by: Dave Jones Debugged-by: Linus Torvalds Signed-off-by: Hugh Dickins Acked-by: Michal Hocko Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- diff --git a/mm/mmap.c b/mm/mmap.c index fcf4c883e21a..0990f8bc0fbe 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1771,7 +1771,8 @@ 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 */ @@ -1874,7 +1875,8 @@ 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 */