From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH v2] mm/mremap: Fail map duplication attempts for private mappings Date: Mon, 24 Jul 2017 10:50:46 +0200 Message-ID: <20170724085045.GD25221@dhcp22.suse.cz> References: <20170720082058.GF9058@dhcp22.suse.cz> <1500583079-26504-1-git-send-email-mike.kravetz@oracle.com> <20170721143644.GC5944@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Mike Kravetz Cc: linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Linux API , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Andrew Morton , Andrea Arcangeli , Aaron Lu , "Kirill A . Shutemov" , Vlastimil Babka , Anshuman Khandual List-Id: linux-api@vger.kernel.org On Fri 21-07-17 14:18:31, Mike Kravetz wrote: [...] > >From 5c4a1602bd6a942544ed011dc0a72fd258e874b2 Mon Sep 17 00:00:00 2001 > From: Mike Kravetz > Date: Wed, 12 Jul 2017 13:52:47 -0700 > Subject: [PATCH] mm/mremap: Fail map duplication attempts for private mappings > > mremap will attempt to create a 'duplicate' mapping if old_size > == 0 is specified. In the case of private mappings, mremap > will actually create a fresh separate private mapping unrelated > to the original. This does not fit with the design semantics of > mremap as the intention is to create a new mapping based on the > original. > > Therefore, return EINVAL in the case where an attempt is made > to duplicate a private mapping. Also, print a warning message > (once) if such an attempt is made. > > Signed-off-by: Mike Kravetz Acked-by: Michal Hocko Thanks! > --- > mm/mremap.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/mm/mremap.c b/mm/mremap.c > index cd8a1b1..75b167d 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -383,6 +383,19 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr, > if (!vma || vma->vm_start > addr) > return ERR_PTR(-EFAULT); > > + /* > + * !old_len is a special case where an attempt is made to 'duplicate' > + * a mapping. This makes no sense for private mappings as it will > + * instead create a fresh/new mapping unrelated to the original. This > + * is contrary to the basic idea of mremap which creates new mappings > + * based on the original. There are no known use cases for this > + * behavior. As a result, fail such attempts. > + */ > + if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) { > + pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap. This is not supported.\n", current->comm, current->pid); > + return ERR_PTR(-EINVAL); > + } > + > if (is_vm_hugetlb_page(vma)) > return ERR_PTR(-EINVAL); > > -- > 2.7.5 -- Michal Hocko SUSE Labs