From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8F775C3A589 for ; Tue, 20 Aug 2019 16:02:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C06B2070B for ; Tue, 20 Aug 2019 16:02:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730256AbfHTQCn (ORCPT ); Tue, 20 Aug 2019 12:02:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48602 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727272AbfHTQCm (ORCPT ); Tue, 20 Aug 2019 12:02:42 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4D86DA35FE7; Tue, 20 Aug 2019 16:02:42 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (ovpn-204-99.brq.redhat.com [10.40.204.99]) by smtp.corp.redhat.com (Postfix) with SMTP id 80BFC6060D; Tue, 20 Aug 2019 16:02:39 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 20 Aug 2019 18:02:41 +0200 (CEST) Date: Tue, 20 Aug 2019 18:02:38 +0200 From: Oleg Nesterov To: Kefeng Wang Cc: linux-mm , Andrea Arcangeli , Peter Xu , Mike Rapoport , Jann Horn , Jason Gunthorpe , Michal Hocko , Andrew Morton , Tetsuo Handa , linux-kernel@vger.kernel.org Subject: [PATCH] userfaultfd_release: always remove uffd flags and clear vm_userfaultfd_ctx Message-ID: <20190820160237.GB4983@redhat.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.68]); Tue, 20 Aug 2019 16:02:42 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org userfaultfd_release() should clear vm_flags/vm_userfaultfd_ctx even if mm->core_state != NULL. Otherwise a page fault can see userfaultfd_missing() == T and use an already freed userfaultfd_ctx. Reported-by: Kefeng Wang Fixes: 04f5866e41fb ("coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping") Cc: stable@vger.kernel.org Signed-off-by: Oleg Nesterov --- fs/userfaultfd.c | 25 +++++++++++++------------ 1 file changed, 13 insertions(+), 12 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index ccbdbd6..fe6d804 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -880,6 +880,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file) /* len == 0 means wake all */ struct userfaultfd_wake_range range = { .len = 0, }; unsigned long new_flags; + bool still_valid; WRITE_ONCE(ctx->released, true); @@ -895,8 +896,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file) * taking the mmap_sem for writing. */ down_write(&mm->mmap_sem); - if (!mmget_still_valid(mm)) - goto skip_mm; + still_valid = mmget_still_valid(mm); prev = NULL; for (vma = mm->mmap; vma; vma = vma->vm_next) { cond_resched(); @@ -907,19 +907,20 @@ static int userfaultfd_release(struct inode *inode, struct file *file) continue; } new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); - prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, - new_flags, vma->anon_vma, - vma->vm_file, vma->vm_pgoff, - vma_policy(vma), - NULL_VM_UFFD_CTX); - if (prev) - vma = prev; - else - prev = vma; + if (still_valid) { + prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, + new_flags, vma->anon_vma, + vma->vm_file, vma->vm_pgoff, + vma_policy(vma), + NULL_VM_UFFD_CTX); + if (prev) + vma = prev; + else + prev = vma; + } vma->vm_flags = new_flags; vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; } -skip_mm: up_write(&mm->mmap_sem); mmput(mm); wakeup: -- 2.5.0