mm: migrate: Close race between migration completion and mprotect
authorMel Gorman <mgorman@suse.de>
Thu, 2 Oct 2014 18:47:41 +0000 (19:47 +0100)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 2 Oct 2014 18:57:18 +0000 (11:57 -0700)
commitd3cb8bf6081b8b7a2dabb1264fe968fd870fa595
tree50783c31445c93012fe0ded14d4a49a03e0d504c
parent50dddff3cb9af328dd42bafe3437c7f47e8b38a9
mm: migrate: Close race between migration completion and mprotect

A migration entry is marked as write if pte_write was true at the time the
entry was created. The VMA protections are not double checked when migration
entries are being removed as mprotect marks write-migration-entries as
read. It means that potentially we take a spurious fault to mark PTEs write
again but it's straight-forward. However, there is a race between write
migrations being marked read and migrations finishing. This potentially
allows a PTE to be write that should have been read. Close this race by
double checking the VMA permissions using maybe_mkwrite when migration
completes.

[torvalds@linux-foundation.org: use maybe_mkwrite]
Cc: stable@vger.kernel.org
Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/migrate.c