userfaultfd: check VM_MAYWRITE was set after verifying the uffd is registered

Calling UFFDIO_UNREGISTER on virtual ranges not yet registered in uffd
could trigger an harmless false positive WARN_ON.  Check the vma is
already registered before checking VM_MAYWRITE to shut off the false
positive warning.

Link: http://lkml.kernel.org/r/20181206212028.18726-2-aarcange@redhat.com
Cc: <stable@vger.kernel.org>
Fixes: 29ec90660d68 ("userfaultfd: shmem/hugetlbfs: only allow to register VM_MAYWRITE vmas")
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: syzbot+06c7092e7d71218a2c16@syzkaller.appspotmail.com
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Orabug: 29163750
CVE: CVE-2018-18397

commit 01e881f5a1fca4677e82733061868c6d6ea05ca7 upstream

Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	fs/userfaultfd.c

Signed-off-by: Shan Hai <shan.hai@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 4d6ccc347e07ad43a29f225b12d9590eec02dc6c..1d1992ec830d03a48a72fc53396c189a1bf3a341 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1104,7 +1104,6 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
                cond_resched();
 
                BUG_ON(vma->vm_ops && !is_vm_hugetlb_page(vma));
-               WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
 
                /*
                 * Nothing to do: this vma is already registered into this
@@ -1113,6 +1112,8 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
                if (!vma->vm_userfaultfd_ctx.ctx)
                        goto skip;
 
+               WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
+
                if (vma->vm_start > start)
                        start = vma->vm_start;
                vma_end = min(end, vma->vm_end);