userfaultfd_copy: return -ENOSPC in case mm has gone

In the non-cooperative userfaultfd case, the process exit may race with
outstanding mcopy_atomic called by the uffd monitor.  Returning -ENOSPC
instead of -EINVAL when mm is already gone will allow uffd monitor to
distinguish this case from other error conditions.

Link: http://lkml.kernel.org/r/1485542673-24387-6-git-send-email-rppt@linux.vnet.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index b676575f226884342e72a7bfe4e2099f3efb8003..625b7285a37be89724f76d86d643c8dd5041f57c 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1607,6 +1607,8 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
                ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
                                   uffdio_copy.len);
                mmput(ctx->mm);
+       } else {
+               return -ENOSPC;
        }
        if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
                return -EFAULT;