mempolicy: mask off internal flags for userspace API

Flags considered internal to the mempolicy kernel code are stored as part
of the "flags" member of struct mempolicy.

Before exposing a policy type to userspace via get_mempolicy(), these
internal flags must be masked.  Flags exposed to userspace, however,
should still be returned to the user.

Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index a37a5034f63d..c94e58b192c3 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -729,7 +729,11 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
         } else {
                 *policy = pol == &default_policy ? MPOL_DEFAULT :
                                                 pol->mode;
-                *policy |= pol->flags;
+                /*
+                 * Internal mempolicy flags must be masked off before exposing
+                 * the policy to userspace.
+                 */
+                *policy |= (pol->flags & MPOL_MODE_FLAGS);
         }
 
         if (vma) {