From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt1-f200.google.com (mail-qt1-f200.google.com [209.85.160.200]) by kanga.kvack.org (Postfix) with ESMTP id BF40B6B7E0B for ; Thu, 6 Dec 2018 22:43:54 -0500 (EST) Received: by mail-qt1-f200.google.com with SMTP id w18so2510554qts.8 for ; Thu, 06 Dec 2018 19:43:54 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id 34si1428571qvs.160.2018.12.06.19.43.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 06 Dec 2018 19:43:54 -0800 (PST) Date: Fri, 7 Dec 2018 11:43:45 +0800 From: Peter Xu Subject: Re: [PATCH 1/1] userfaultfd: check VM_MAYWRITE was set after verifying the uffd is registered Message-ID: <20181207034345.GC10726@xz-x1> References: <20181206212028.18726-1-aarcange@redhat.com> <20181206212028.18726-2-aarcange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181206212028.18726-2-aarcange@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Arcangeli Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Mike Rapoport , Mike Kravetz , Jann Horn , "Dr. David Alan Gilbert" On Thu, Dec 06, 2018 at 04:20:28PM -0500, Andrea Arcangeli wrote: > 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. > > Cc: > Fixes: 29ec90660d68 ("userfaultfd: shmem/hugetlbfs: only allow to register VM_MAYWRITE vmas") > Reported-by: syzbot+06c7092e7d71218a2c16@syzkaller.appspotmail.com > Signed-off-by: Andrea Arcangeli > --- > fs/userfaultfd.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index cd58939dc977..7a85e609fc27 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -1566,7 +1566,6 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, > cond_resched(); > > BUG_ON(!vma_can_userfault(vma)); > - WARN_ON(!(vma->vm_flags & VM_MAYWRITE)); > > /* > * Nothing to do: this vma is already registered into this Maybe we want to fix this comment too some day: /* * Nothing to do: this vma is already registered into this * userfaultfd and with the right tracking mode too. */ But I don't think it's anything urgent since it's clear it means the other way round and it can potentially be touched up in any further cleanup/fixes of uffd. Acked-by: Peter Xu > @@ -1575,6 +1574,8 @@ 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); Thanks, -- Peter Xu