linux-kernel - [PATCH 0/1] userfaultfd: check VM_MAYWRITE was set after verifying the uffd is registered

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Date:   Thu,  6 Dec 2018 16:20:27 -0500
From:   Andrea Arcangeli <aarcange@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Hugh Dickins <hughd@...gle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Jann Horn <jannh@...gle.com>, Peter Xu <peterx@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Subject: [PATCH 0/1] userfaultfd: check VM_MAYWRITE was set after verifying the uffd is registered

Hello,

The juxtaposition with the other bugchecks didn't make it apparent
that the this WARN_ON was one line too soon.

An app trying to unregister a not-yet-registered range will trigger an
_harmless_ false positive WARN_ON. No real app would do that so it
went unnoticed during testing.

This should be applied on top of 29ec90660d68 ("userfaultfd:
shmem/hugetlbfs: only allow to register VM_MAYWRITE vmas") to shut off
the false positive warning.

Thanks,
Andrea

Andrea Arcangeli (1):
  userfaultfd: check VM_MAYWRITE was set after verifying the uffd is
    registered

 fs/userfaultfd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)