Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757119AbdLWAZT (ORCPT ); Fri, 22 Dec 2017 19:25:19 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52474 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756958AbdLWAZH (ORCPT ); Fri, 22 Dec 2017 19:25:07 -0500 From: Andrea Arcangeli To: Andrew Morton , Eric Biggers Cc: Mike Rapoport , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com Subject: [PATCH 1/1] userfaultfd: clear the vma->vm_userfaultfd_ctx if UFFD_EVENT_FORK fails Date: Sat, 23 Dec 2017 01:25:05 +0100 Message-Id: <20171223002505.593-2-aarcange@redhat.com> In-Reply-To: <20171223002505.593-1-aarcange@redhat.com> References: <20171222222346.GB28786@zzz.localdomain> <20171223002505.593-1-aarcange@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Sat, 23 Dec 2017 00:25:07 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2029 Lines: 62 The previous fix 384632e67e0829deb8015ee6ad916b180049d252 corrected the refcounting in case of UFFD_EVENT_FORK failure for the fork userfault paths. That still didn't clear the vma->vm_userfaultfd_ctx of the vmas that were set to point to the aborted new uffd ctx earlier in dup_userfaultfd. Cc: stable@vger.kernel.org Signed-off-by: Andrea Arcangeli --- fs/userfaultfd.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 896f810b6a06..1a88916455bd 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -591,11 +591,14 @@ int handle_userfault(struct vm_fault *vmf, unsigned long reason) static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx, struct userfaultfd_wait_queue *ewq) { + struct userfaultfd_ctx *release_new_ctx; + if (WARN_ON_ONCE(current->flags & PF_EXITING)) goto out; ewq->ctx = ctx; init_waitqueue_entry(&ewq->wq, current); + release_new_ctx = NULL; spin_lock(&ctx->event_wqh.lock); /* @@ -622,8 +625,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx, new = (struct userfaultfd_ctx *) (unsigned long) ewq->msg.arg.reserved.reserved1; - - userfaultfd_ctx_put(new); + release_new_ctx = new; } break; } @@ -638,6 +640,20 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx, __set_current_state(TASK_RUNNING); spin_unlock(&ctx->event_wqh.lock); + if (release_new_ctx) { + struct vm_area_struct *vma; + struct mm_struct *mm = release_new_ctx->mm; + + /* the various vma->vm_userfaultfd_ctx still points to it */ + down_write(&mm->mmap_sem); + for (vma = mm->mmap; vma; vma = vma->vm_next) + if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) + vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; + up_write(&mm->mmap_sem); + + userfaultfd_ctx_put(release_new_ctx); + } + /* * ctx may go away after this if the userfault pseudo fd is * already released.