userfaultfd: non-cooperative: robustness check

Similar to the handle_userfault() case, also make sure to never attempt
to send any event past the PF_EXITING point of no return.

This is purely a robustness check.

Link: http://lkml.kernel.org/r/20170224181957.19736-3-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 16d0cc600fa9..668bbbd2e04d 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -530,8 +530,13 @@ out:
 static int userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
                                              struct userfaultfd_wait_queue *ewq)
 {
-        int ret = 0;
+        int ret;
+
+        ret = -1;
+        if (WARN_ON_ONCE(current->flags & PF_EXITING))
+                goto out;
 
+        ret = 0;
         ewq->ctx = ctx;
         init_waitqueue_entry(&ewq->wq, current);
 
@@ -566,7 +571,7 @@ static int userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
          * ctx may go away after this if the userfault pseudo fd is
          * already released.
          */
-
+out:
         userfaultfd_ctx_put(ctx);
         return ret;
 }