From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Brauner Subject: [PATCH 2/3] ecryptfs: use private mount in path Date: Fri, 9 Apr 2021 18:24:21 +0200 Message-ID: <20210409162422.1326565-3-brauner@kernel.org> References: <20210409162422.1326565-1-brauner@kernel.org> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: Received: from mail.kernel.org ([198.145.29.99]:34186 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231946AbhDIQ0O (ORCPT ); Fri, 9 Apr 2021 12:26:14 -0400 In-Reply-To: <20210409162422.1326565-1-brauner@kernel.org> List-ID: Content-Type: text/plain; charset="us-ascii" To: Tyler Hicks , ecryptfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, Amir Goldstein , Christian Brauner From: Christian Brauner Since [1] we support creating private mounts from a given path's vfsmount. This makes them very suitable for any filesystem or filesystem functionality that piggybacks on paths of another filesystem. Overlayfs, cachefiles, and ecryptfs are three prime examples. Since private mounts aren't attached in the filesystem they aren't affected by mount property changes after ecryptfs makes use of them. This seems a rather desirable property as the underlying path can't e.g. suddenly go from read-write to read-only and in general it means that ecryptfs is always in full control of the underlying mount after the user has allowed it to be used (apart from operations that affect the superblock of course). Besides that it also makes things simpler for a variety of other vfs features. One concrete example is fanotify. When the path->mnt of the path that is used as a cache has been marked with FAN_MARK_MOUNT the semantics get tricky as it isn't clear whether the watchers of path->mnt should get notified about fsnotify events when files are created by cachefilesd via path->mnt. Using a private mount let's us elegantly handle this case too and aligns the behavior of stacks created by overlayfs and cachefiles. Reading through the codebase of ecryptfs it currently takes path->mnt and then retrieves that path whenever it needs to perform operations in the underlying filesystem. Simply drop the old path->mnt once we've created a private mount and place the new private mnt into path->mnt. This should be all that is needed to make this work since ecryptfs uses the same lower path's vfsmount to construct the paths it uses to operate on the underlying filesystem. [1]: c771d683a62e ("vfs: introduce clone_private_mount()") Cc: Amir Goldstein Cc: Tyler Hicks Cc: ecryptfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner --- fs/ecryptfs/main.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c index cdf40a54a35d..9dcf9a0dd37b 100644 --- a/fs/ecryptfs/main.c +++ b/fs/ecryptfs/main.c @@ -476,6 +476,7 @@ static struct file_system_type ecryptfs_fs_type; static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags, const char *dev_name, void *raw_data) { + struct vfsmount *mnt = NULL; struct super_block *s; struct ecryptfs_sb_info *sbi; struct ecryptfs_mount_crypt_stat *mount_crypt_stat; @@ -537,6 +538,14 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags goto out_free; } + mnt = clone_private_mount(&path); + if (IS_ERR(mnt)) { + rc = PTR_ERR(mnt); + mnt = NULL; + pr_warn("Failed to create private mount for ecryptfs\n"); + goto out_free; + } + if (check_ruid && !uid_eq(d_inode(path.dentry)->i_uid, current_uid())) { rc = -EPERM; printk(KERN_ERR "Mount of device (uid: %d) not owned by " @@ -592,6 +601,13 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags /* ->kill_sb() will take care of root_info */ ecryptfs_set_dentry_private(s->s_root, root_info); + + /* We've created a private clone of this mount above so drop it now. */ + mntput(path.mnt); + + /* Use our private mount from now on. */ + path.mnt = mnt; + root_info->lower_path = path; s->s_flags |= SB_ACTIVE; @@ -599,6 +615,7 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags out_free: path_put(&path); + mntput(mnt); out1: deactivate_locked_super(s); out: -- 2.27.0