From patchwork Sat May 15 00:27:19 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 439824 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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED 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 4A648C433B4 for ; Sat, 15 May 2021 00:27:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2F80661457 for ; Sat, 15 May 2021 00:27:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234517AbhEOA2c (ORCPT ); Fri, 14 May 2021 20:28:32 -0400 Received: from mail.kernel.org ([198.145.29.99]:43708 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230022AbhEOA2b (ORCPT ); Fri, 14 May 2021 20:28:31 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8BAEC61176; Sat, 15 May 2021 00:27:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1621038439; bh=KsHlOjWWpiWbhUWj38CsS3aihRqJiw43myh9AH5dSng=; h=Date:From:To:Subject:In-Reply-To:From; b=t3f/TrCCXtal0pbeCTx/WmCrpSeCvvAIlJ/5ZFjnQ2enlcBkDGHY8Uk8Bdy/L1BCo NFVxEpjU3kDwmS//F12UAe/HwkXeAK9oC5D2J2sG/MsW6d9W6O/SXf1dqwj+QXeFmE RlOeO5JXkDJZnXYfaY1FzVXiQx5yBE+HpzdWLfz8= Date: Fri, 14 May 2021 17:27:19 -0700 From: Andrew Morton To: akpm@linux-foundation.org, axelrasmussen@google.com, hughd@google.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, peterx@redhat.com, stable@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 06/13] userfaultfd: release page in error path to avoid BUG_ON Message-ID: <20210515002719.QX9ZRXcYB%akpm@linux-foundation.org> In-Reply-To: <20210514172634.9018621171d5334ceee97e95@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Axel Rasmussen Subject: userfaultfd: release page in error path to avoid BUG_ON Consider the following sequence of events: 1. Userspace issues a UFFD ioctl, which ends up calling into shmem_mfill_atomic_pte(). We successfully account the blocks, we shmem_alloc_page(), but then the copy_from_user() fails. We return -ENOENT. We don't release the page we allocated. 2. Our caller detects this error code, tries the copy_from_user() after dropping the mmap_lock, and retries, calling back into shmem_mfill_atomic_pte(). 3. Meanwhile, let's say another process filled up the tmpfs being used. 4. So shmem_mfill_atomic_pte() fails to account blocks this time, and immediately returns - without releasing the page. This triggers a BUG_ON in our caller, which asserts that the page should always be consumed, unless -ENOENT is returned. To fix this, detect if we have such a "dangling" page when accounting fails, and if so, release it before returning. Link: https://lkml.kernel.org/r/20210428230858.348400-1-axelrasmussen@google.com Fixes: cb658a453b93 ("userfaultfd: shmem: avoid leaking blocks and used blocks in UFFDIO_COPY") Signed-off-by: Axel Rasmussen Reported-by: Hugh Dickins Acked-by: Hugh Dickins Reviewed-by: Peter Xu Cc: Signed-off-by: Andrew Morton --- mm/shmem.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) --- a/mm/shmem.c~userfaultfd-release-page-in-error-path-to-avoid-bug_on +++ a/mm/shmem.c @@ -2361,8 +2361,18 @@ static int shmem_mfill_atomic_pte(struct pgoff_t offset, max_off; ret = -ENOMEM; - if (!shmem_inode_acct_block(inode, 1)) + if (!shmem_inode_acct_block(inode, 1)) { + /* + * We may have got a page, returned -ENOENT triggering a retry, + * and now we find ourselves with -ENOMEM. Release the page, to + * avoid a BUG_ON in our caller. + */ + if (unlikely(*pagep)) { + put_page(*pagep); + *pagep = NULL; + } goto out; + } if (!*pagep) { page = shmem_alloc_page(gfp, info, pgoff);