From patchwork Fri Aug 24 16:16:36 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 10575569 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 23C5C920 for ; Fri, 24 Aug 2018 16:24:08 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 170E22CA56 for ; Fri, 24 Aug 2018 16:24:08 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 152A92CA62; Fri, 24 Aug 2018 16:24:08 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 28B182CA56 for ; Fri, 24 Aug 2018 16:24:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727854AbeHXT6y (ORCPT ); Fri, 24 Aug 2018 15:58:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:41470 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727610AbeHXT6v (ORCPT ); Fri, 24 Aug 2018 15:58:51 -0400 Received: from sol.localdomain (c-67-185-97-198.hsd1.wa.comcast.net [67.185.97.198]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 70B302157C; Fri, 24 Aug 2018 16:23:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1535127809; bh=P31b+DPN7NsxK6ZyE5u6BLZQnVKtt0YRPSEZDElIG4I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Io2Otakc2+4Vf3YD1nF/V5mibosT9fKtOBCzY/G8C7u9DSni8hr3VVO+D6Xq81+mU I9BqGLxLcuKkyy77digkvix1sPDb8IUq6LlZl7qg8wilXSF8uele8fYswc6wZ/2vBA WSe4rW8auBQQJGDk7swOYGIJllACNz0hyjDAUzqs= From: Eric Biggers To: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Cc: linux-integrity@vger.kernel.org, linux-fscrypt@vger.kernel.org, linux-kernel@vger.kernel.org, Mimi Zohar , Dmitry Kasatkin , Michael Halcrow , Victor Hsieh Subject: [RFC PATCH 04/10] fs-verity: implement FS_IOC_MEASURE_VERITY ioctl Date: Fri, 24 Aug 2018 09:16:36 -0700 Message-Id: <20180824161642.1144-5-ebiggers@kernel.org> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180824161642.1144-1-ebiggers@kernel.org> References: <20180824161642.1144-1-ebiggers@kernel.org> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Eric Biggers Add a function for filesystems to call to implement the FS_IOC_MEASURE_VERITY ioctl. This ioctl retrieves the file measurement hash that fs-verity calculated for the given file and is enforcing for reads; i.e., reads that don't match this hash will fail. This ioctl can be used to implement lightweight auditing or authentication of file hashes in userspace, as an alternative to an in-kernel policy such as an IMA policy. Note that due to fs-verity's use of a Merkle tree, opening a file and executing this ioctl takes constant time, regardless of the file's size. Signed-off-by: Eric Biggers --- fs/verity/ioctl.c | 49 ++++++++++++++++++++++++++++++++++++++++ fs/verity/setup.c | 4 +++- include/linux/fsverity.h | 6 +++++ 3 files changed, 58 insertions(+), 1 deletion(-) diff --git a/fs/verity/ioctl.c b/fs/verity/ioctl.c index 993f2afdcc734..3da9b0f441c13 100644 --- a/fs/verity/ioctl.c +++ b/fs/verity/ioctl.c @@ -119,3 +119,52 @@ int fsverity_ioctl_enable(struct file *filp, const void __user *arg) return err; } EXPORT_SYMBOL_GPL(fsverity_ioctl_enable); + +/** + * fsverity_ioctl_measure - get a verity file's measurement + * + * The FS_IOC_MEASURE_VERITY ioctl retrieves the file measurement that the + * kernel is enforcing for reads from a verity file. + * + * No privileges are required to use this ioctl, since it is a read-only + * operation on a single regular file. + * + * Return: 0 on success, -errno on failure + */ +int fsverity_ioctl_measure(struct file *filp, void __user *_uarg) +{ + const struct inode *inode = file_inode(filp); + struct fsverity_digest __user *uarg = _uarg; + const struct fsverity_info *vi; + const struct fsverity_hash_alg *hash_alg; + struct fsverity_digest arg; + + vi = get_fsverity_info(inode); + if (!vi) + return -ENODATA; /* not a verity file */ + hash_alg = vi->hash_alg; + + /* + * The user specifies the digest_size their buffer has space for; we can + * return the digest if it fits in the available space. We write back + * the actual size, which may be shorter than the user-specified size. + */ + + if (get_user(arg.digest_size, &uarg->digest_size)) + return -EFAULT; + if (arg.digest_size < hash_alg->digest_size) + return -EOVERFLOW; + + memset(&arg, 0, sizeof(arg)); + arg.digest_algorithm = hash_alg - fsverity_hash_algs; + arg.digest_size = hash_alg->digest_size; + + if (copy_to_user(uarg, &arg, sizeof(arg))) + return -EFAULT; + + if (copy_to_user(uarg->digest, vi->measurement, hash_alg->digest_size)) + return -EFAULT; + + return 0; +} +EXPORT_SYMBOL_GPL(fsverity_ioctl_measure); diff --git a/fs/verity/setup.c b/fs/verity/setup.c index 84cc2edeca25b..3f5cb9526dbc9 100644 --- a/fs/verity/setup.c +++ b/fs/verity/setup.c @@ -842,7 +842,9 @@ static int __init fsverity_module_init(void) goto error; err = -ENOMEM; - fsverity_info_cachep = KMEM_CACHE(fsverity_info, SLAB_RECLAIM_ACCOUNT); + fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info, + SLAB_RECLAIM_ACCOUNT, + measurement); if (!fsverity_info_cachep) goto error_free_workqueue; diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h index c710b6b5fb4a6..9d3371dbd262f 100644 --- a/include/linux/fsverity.h +++ b/include/linux/fsverity.h @@ -23,6 +23,7 @@ struct fsverity_operations { /* ioctl.c */ extern int fsverity_ioctl_enable(struct file *filp, const void __user *arg); +extern int fsverity_ioctl_measure(struct file *filp, void __user *arg); /* setup.c */ extern int fsverity_file_open(struct inode *inode, struct file *filp); @@ -46,6 +47,11 @@ static inline int fsverity_ioctl_enable(struct file *filp, return -EOPNOTSUPP; } +static inline int fsverity_ioctl_measure(struct file *filp, void __user *arg) +{ + return -EOPNOTSUPP; +} + /* setup.c */ static inline int fsverity_file_open(struct inode *inode, struct file *filp)