From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753094AbdGMWeO (ORCPT ); Thu, 13 Jul 2017 18:34:14 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:44318 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752919AbdGMWeM (ORCPT ); Thu, 13 Jul 2017 18:34:12 -0400 Subject: Re: [PATCH] mm/mremap: Fail map duplication attempts for private mappings To: Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1499961495-8063-1-git-send-email-mike.kravetz@oracle.com> <4e921eb5-8741-3337-9a7d-5ec9473412da@suse.cz> Cc: Andrew Morton , Andrea Arcangeli , Michal Hocko , Aaron Lu , "Kirill A . Shutemov" , Anshuman Khandual , Linux API From: Mike Kravetz Message-ID: <415625d2-1be9-71f0-ca11-a014cef98a3f@oracle.com> Date: Thu, 13 Jul 2017 15:33:47 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <4e921eb5-8741-3337-9a7d-5ec9473412da@suse.cz> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/13/2017 12:11 PM, Vlastimil Babka wrote: > [+CC linux-api] > > On 07/13/2017 05:58 PM, Mike Kravetz wrote: >> mremap will create a 'duplicate' mapping if old_size == 0 is >> specified. Such duplicate mappings make no sense for private >> mappings. If duplication is attempted for a private mapping, >> mremap creates a separate private mapping unrelated to the >> original mapping and makes no modifications to the original. >> This is contrary to the purpose of mremap which should return >> a mapping which is in some way related to the original. >> >> Therefore, return EINVAL in the case where if an attempt is >> made to duplicate a private mapping. >> >> Signed-off-by: Mike Kravetz > > Acked-by: Vlastimil Babka > In another e-mail thread, Andrea makes the case that mremap(old_size == 0) of private file backed mappings could possibly be used for something useful. For example to create a private COW mapping. Of course, a better way to do this would be simply using the fd to create a private mapping. If returning EINVAL for all private mappings is too general, the following patch adds a check to only return EINVAL for private anon mappings. mm/mremap: Fail map duplication attempts for private anon mappings mremap will create a 'duplicate' mapping if old_size == 0 is specified. Such duplicate mappings make no sense for private anonymous mappings. If duplication is attempted for a private anon mapping, mremap creates a separate private mapping unrelated to the original mapping and makes no modifications to the original. This is contrary to the purpose of mremap which should return a mapping which is in some way related to the original. Therefore, return EINVAL in the case where an attempt is made to duplicate a private anon mapping. Signed-off-by: Mike Kravetz --- mm/mremap.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/mremap.c b/mm/mremap.c index cd8a1b1..586ea3d 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -383,6 +383,14 @@ 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 a mapping is 'duplicated'. + * Do not allow this for private anon mappings. + */ + if (!old_len && vma_is_anonymous(vma) && + !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) + return ERR_PTR(-EINVAL); + if (is_vm_hugetlb_page(vma)) return ERR_PTR(-EINVAL); -- 2.7.5