Patch "mm: fix new crash in unmapped_area_topdown()" has been added to the 3.18-stable tree

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 3.18-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-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Hugh Dickins <[email protected]>
Date: Tue, 20 Jun 2017 02:10:44 -0700
Subject: mm: fix new crash in unmapped_area_topdown()

From: Hugh Dickins <[email protected]>

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().

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

@@ -1770,7 +1770,8 @@ 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 */

@@ -1873,7 +1874,8 @@ 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 [email protected] are

queue-3.18/mm-fix-new-crash-in-unmapped_area_topdown.patch queue-3.18/allow-stack-to-grow-up-to-address-space-limit.patch queue-3.18/mm-larger-stack-guard-gap-between-vmas.patch