Patch "mm: fix new crash in unmapped_area_topdown()" has been added to the 4.9-stable tree

Patch "mm: fix new crash in unmapped_area_topdown()" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    mm: fix new crash in unmapped_area_topdown()

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-fix-new-crash-in-unmapped_area_topdown.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From f4cb767d76cf7ee72f97dd76f6cfa6c76a5edc89 Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hughd@google.com>
Date: Tue, 20 Jun 2017 02:10:44 -0700
Subject: mm: fix new crash in unmapped_area_topdown()

From: Hugh Dickins <hughd@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().

Fixes: 1be7107fbe18 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/mmap.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1813,7 +1813,8 @@ 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 */
@@ -1916,7 +1917,8 @@ 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 */


Patches currently in stable-queue which might be from hughd@google.com are

queue-4.9/mm-fix-new-crash-in-unmapped_area_topdown.patch
queue-4.9/allow-stack-to-grow-up-to-address-space-limit.patch
queue-4.9/mm-larger-stack-guard-gap-between-vmas.patch