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=-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_RED autolearn=unavailable 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 D9687C433B4 for ; Mon, 10 May 2021 05:33:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9D4F26143C for ; Mon, 10 May 2021 05:33:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229986AbhEJFeu (ORCPT ); Mon, 10 May 2021 01:34:50 -0400 Received: from mail.kernel.org ([198.145.29.99]:53232 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230056AbhEJFet (ORCPT ); Mon, 10 May 2021 01:34:49 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id B770460FF2; Mon, 10 May 2021 05:33:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1620624819; bh=gM/aJSbq3DQ9Rbro5Qyk0Iv2OGxSteSR9ZllfE5VKLk=; h=Date:From:To:Subject:From; b=S2WK7TZhwQK6tqS1fOrCl1TNb6cbGZXQRCEJ8IJ/qhP+fLyze+6DSNkVG7YeOsbjr VQYeZms+uEKK/MbCRkJR50LaMlOzACxhTt4JWUzT3VvbCXA5SqPVTiZJb5JG/MCm+g Nb0zIv+CRKUZvV4t0OjqDFLNhUyi9WsCyB5RNhFo= Date: Sun, 09 May 2021 22:33:39 -0700 From: akpm@linux-foundation.org To: axelrasmussen@google.com, hughd@google.com, mm-commits@vger.kernel.org, peterx@redhat.com, stable@vger.kernel.org Subject: + userfaultfd-release-page-in-error-path-to-avoid-bug_on.patch added to -mm tree Message-ID: <20210510053339.91US3w9Em%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The patch titled Subject: userfaultfd: release page in error path to avoid BUG_ON has been added to the -mm tree. Its filename is userfaultfd-release-page-in-error-path-to-avoid-bug_on.patch This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/userfaultfd-release-page-in-error-path-to-avoid-bug_on.patch and later at https://ozlabs.org/~akpm/mmotm/broken-out/userfaultfd-release-page-in-error-path-to-avoid-bug_on.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ 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); _ Patches currently in -mm which might be from axelrasmussen@google.com are userfaultfd-release-page-in-error-path-to-avoid-bug_on.patch userfaultfd-hugetlbfs-avoid-including-userfaultfd_kh-in-hugetlbh.patch userfaultfd-shmem-combine-shmem_mcopy_atomicmfill_zeropage_pte.patch userfaultfd-shmem-support-minor-fault-registration-for-shmem.patch userfaultfd-shmem-support-uffdio_continue-for-shmem.patch userfaultfd-shmem-advertise-shmem-minor-fault-support.patch userfaultfd-shmem-modify-shmem_mfill_atomic_pte-to-use-install_pte.patch userfaultfd-selftests-use-memfd_create-for-shmem-test-type.patch userfaultfd-selftests-create-alias-mappings-in-the-shmem-test.patch userfaultfd-selftests-reinitialize-test-context-in-each-test.patch userfaultfd-selftests-exercise-minor-fault-handling-shmem-support.patch