From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753791AbbGAXEr (ORCPT ); Wed, 1 Jul 2015 19:04:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35019 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753819AbbGAXEh (ORCPT ); Wed, 1 Jul 2015 19:04:37 -0400 Date: Thu, 2 Jul 2015 01:03:11 +0200 From: Oleg Nesterov To: Andrew Morton Cc: Benjamin LaHaise , David Rientjes , Hugh Dickins , Jeff Moyer , Kirill Shutemov , Pavel Emelyanov , linux-kernel@vger.kernel.org Subject: [PATCH v2 4/5] mremap: don't do uneccesary checks if new_len == old_len Message-ID: <20150701230311.GA18036@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150701230244.GA18003@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The "new_len > old_len" branch in vma_to_resize() looks very confusing. It only covers the VM_DONTEXPAND/pgoff checks but everything below is equally unneeded if new_len == old_len. Change this code to return if "new_len == old_len", new_len < old_len is not possible, otherwise the code below is wrong anyway. Signed-off-by: Oleg Nesterov Acked-by: David Rientjes --- mm/mremap.c | 21 +++++++++++---------- 1 files changed, 11 insertions(+), 10 deletions(-) diff --git a/mm/mremap.c b/mm/mremap.c index 7dcf7b4..d3f42be 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -346,6 +346,7 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr, { struct mm_struct *mm = current->mm; struct vm_area_struct *vma = find_vma(mm, addr); + unsigned long pgoff; if (!vma || vma->vm_start > addr) return ERR_PTR(-EFAULT); @@ -357,17 +358,17 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr, if (old_len > vma->vm_end - addr) return ERR_PTR(-EFAULT); + if (new_len == old_len) + return vma; + /* Need to be careful about a growing mapping */ - if (new_len > old_len) { - unsigned long pgoff; - - if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) - return ERR_PTR(-EFAULT); - pgoff = (addr - vma->vm_start) >> PAGE_SHIFT; - pgoff += vma->vm_pgoff; - if (pgoff + (new_len >> PAGE_SHIFT) < pgoff) - return ERR_PTR(-EINVAL); - } + pgoff = (addr - vma->vm_start) >> PAGE_SHIFT; + pgoff += vma->vm_pgoff; + if (pgoff + (new_len >> PAGE_SHIFT) < pgoff) + return ERR_PTR(-EINVAL); + + if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) + return ERR_PTR(-EFAULT); if (vma->vm_flags & VM_LOCKED) { unsigned long locked, lock_limit; -- 1.5.5.1