From patchwork Tue Jul 13 11:13:41 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Brauner X-Patchwork-Id: 12373687 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=-19.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 33315C07E95 for ; Tue, 13 Jul 2021 11:17:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 20E6F61288 for ; Tue, 13 Jul 2021 11:17:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236045AbhGMLTy (ORCPT ); Tue, 13 Jul 2021 07:19:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:47634 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235932AbhGMLTx (ORCPT ); Tue, 13 Jul 2021 07:19:53 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id AB24D6023F; Tue, 13 Jul 2021 11:17:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1626175023; bh=/cn7CXHyFFjdCM6hf0uMa3DF0r9KkC6Av6VBa32UgCM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tF/vv8F9/o6IPtwWG9LmPP8ce7wZobFgP8Pf/fpMbN0oDQXmD13p8RCTcNCKC6wrB Wx2ltCEBxJg1bwWPfLpjB8OIdbNqcUPUurKXmv6O1w2AO18T90ae1hqQX7B46xGDg4 3rFWmcBnihSl2eRB337vOYQsYscvjt5Fehcvooj774+y9zvYJK4+rl814GgYp5ZjPs mL+9n6tmlmuEmmwig/rlWmP2KGUNNGz7iXKjlY/0teFVKdB1QabGBADf9vWOgHUgOc LVEFLq2fGajwp4LJJJmDq4cm9wNzMVDQ4r3qgdtJwzzc/iCb8/z/pc74ftoHi4PIMp 4vjz+zBq2HGaw== From: Christian Brauner To: Christoph Hellwig , Chris Mason , Josef Bacik , David Sterba , Al Viro Cc: linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, Christian Brauner , Christoph Hellwig Subject: [PATCH 21/24] btrfs/ioctl: allow idmapped BTRFS_IOC_INO_LOOKUP_USER ioctl Date: Tue, 13 Jul 2021 13:13:41 +0200 Message-Id: <20210713111344.1149376-22-brauner@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210713111344.1149376-1-brauner@kernel.org> References: <20210713111344.1149376-1-brauner@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3737; h=from:subject; bh=NuuA7EtYgP3uwobv3xcJsDqZuSmPZC6F7vuwUE3D+Zc=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMSS8LY2NialIn3b/7tI3zXcmrFmRMZm30YPX747uzberdH5t r8h/2lHKwiDGxSArpsji0G4SLrecp2KzUaYGzBxWJpAhDFycAjCRG7sYGc4HVmoIHHy2TnplT+e7pb etn/eE7T5RIP/2R/UEQw25yJ+MDOsyLQy/nTjSq5/2NcU3wqUtXGdzV//BMm+rwLs6Um08jAA= X-Developer-Key: i=christian.brauner@ubuntu.com; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Christian Brauner The BTRFS_IOC_INO_LOOKUP_USER is an unprivileged version of the BTRFS_IOC_INO_LOOKUP ioctl and has the following restrictions. The main difference between the two is that BTRFS_IOC_INO_LOOKUP is filesystem wide operation wheres BTRFS_IOC_INO_LOOKUP_USER is scoped beneath the file descriptor passed with the ioctl. Specifically, BTRFS_IOC_INO_LOOKUP_USER must adhere to the following restrictions: - The caller must be privileged over each inode of each path component for the path they are trying to lookup. - The path for the subvolume the caller is trying to lookup must be reachable from the inode associated with the file descriptor passed with the ioctl. The second condition makes it possible to scope the lookup of the path to the mount identified by the file descriptor passed with the ioctl. This allows us to enable this ioctl on idmapped mounts. Specifically, this is possible because all child subvolumes of a parent subvolume are reachable when the parent subvolume is mounted. So if the user had access to open the parent subvolume or has been given the fd then they can lookup the path if they had access to it provided they were privileged over each path component. Note, the BTRFS_IOC_INO_LOOKUP_USER ioctl allows a user to learn the path and name of a subvolume even though they would otherwise be restricted from doing so via regular vfs-based lookup. So think about a parent subvolume with multiple child subvolumes. Someone could mount he parent subvolume and restrict access to the child subvolumes by overmounting them with empty directories. At this point the user can't traverse the child subvolumes and they can't open files in the child subvolumes. However, they can still learn the path of child subvolumes as long as they have access to the parent subvolume by using the BTRFS_IOC_INO_LOOKUP_USER ioctl. The underlying assumption here is that it's ok that the lookup ioctls can't really take mounts into account other than the original mount the fd belongs to during lookup. Since this assumption is baked into the original BTRFS_IOC_INO_LOOKUP_USER ioctl we can extend it to idmapped mounts. Cc: Chris Mason Cc: Josef Bacik Cc: Christoph Hellwig Cc: David Sterba Cc: linux-btrfs@vger.kernel.org Signed-off-by: Christian Brauner --- fs/btrfs/ioctl.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 8c1ca9f05f4f..f56b4e159099 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -2439,7 +2439,8 @@ static noinline int btrfs_search_path_in_tree(struct btrfs_fs_info *info, return ret; } -static int btrfs_search_path_in_tree_user(struct inode *inode, +static int btrfs_search_path_in_tree_user(struct user_namespace *mnt_userns, + struct inode *inode, struct btrfs_ioctl_ino_lookup_user_args *args) { struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info; @@ -2537,7 +2538,7 @@ static int btrfs_search_path_in_tree_user(struct inode *inode, ret = PTR_ERR(temp_inode); goto out_put; } - ret = inode_permission(&init_user_ns, temp_inode, + ret = inode_permission(mnt_userns, temp_inode, MAY_READ | MAY_EXEC); iput(temp_inode); if (ret) { @@ -2679,7 +2680,7 @@ static int btrfs_ioctl_ino_lookup_user(struct file *file, void __user *argp) return -EACCES; } - ret = btrfs_search_path_in_tree_user(inode, args); + ret = btrfs_search_path_in_tree_user(file_mnt_user_ns(file), inode, args); if (ret == 0 && copy_to_user(argp, args, sizeof(*args))) ret = -EFAULT;