userfaultfd: wp: declare _UFFDIO_WRITEPROTECT conditionally

Only declare _UFFDIO_WRITEPROTECT if the user specified
UFFDIO_REGISTER_MODE_WP and if all the checks passed.  Then when the user
registers regions with shmem/hugetlbfs we won't expose the new ioctl to
them.  Even with complete anonymous memory range, we'll only expose the
new WP ioctl bit if the register mode has MODE_WP.

Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Link: http://lkml.kernel.org/r/20200220163112.11409-18-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 6e878d2..e39fdec 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1495,14 +1495,24 @@ out_unlock:
        up_write(&mm->mmap_sem);
        mmput(mm);
        if (!ret) {
+               __u64 ioctls_out;
+
+               ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
+                   UFFD_API_RANGE_IOCTLS;
+
+               /*
+                * Declare the WP ioctl only if the WP mode is
+                * specified and all checks passed with the range
+                */
+               if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
+                       ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
+
                /*
                 * Now that we scanned all vmas we can already tell
                 * userland which ioctls methods are guaranteed to
                 * succeed on this range.
                 */
-               if (put_user(basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
-                            UFFD_API_RANGE_IOCTLS,
-                            &user_uffdio_register->ioctls))
+               if (put_user(ioctls_out, &user_uffdio_register->ioctls))
                        ret = -EFAULT;
        }
 out: