From patchwork Thu May 14 17:33:09 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Eric W. Biederman" X-Patchwork-Id: 6408751 Return-Path: X-Original-To: patchwork-linux-fsdevel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 2FB419F32B for ; Thu, 14 May 2015 17:38:09 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 426AA20444 for ; Thu, 14 May 2015 17:38:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 21F1B2027D for ; Thu, 14 May 2015 17:38:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030185AbbENRiE (ORCPT ); Thu, 14 May 2015 13:38:04 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:33168 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933636AbbENRh7 (ORCPT ); Thu, 14 May 2015 13:37:59 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out02.mta.xmission.com with esmtps (TLS1.2:DHE_RSA_AES_128_CBC_SHA1:128) (Exim 4.82) (envelope-from ) id 1Ysx54-0002aG-0V; Thu, 14 May 2015 11:37:58 -0600 Received: from 67-3-205-90.omah.qwest.net ([67.3.205.90] helo=x220.int.ebiederm.org.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:DHE_RSA_AES_128_CBC_SHA1:128) (Exim 4.82) (envelope-from ) id 1Ysx52-0000b7-QK; Thu, 14 May 2015 11:37:57 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Linux Containers Cc: , Linux API , "Serge E. Hallyn" , Andy Lutomirski , Richard Weinberger , Kenton Varda , Michael Kerrisk-manpages , =?utf-8?Q?St=C3=A9phane?= Graber , Eric Windisch , Greg Kroah-Hartman , Tejun Heo References: <87pp63jcca.fsf@x220.int.ebiederm.org> Date: Thu, 14 May 2015 12:33:09 -0500 In-Reply-To: <87pp63jcca.fsf@x220.int.ebiederm.org> (Eric W. Biederman's message of "Thu, 14 May 2015 12:30:45 -0500") Message-ID: <87382zjc8a.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 X-XM-AID: U2FsdGVkX1+EIKT5nqbiBTT5pnxK4QwjLJSqZPI6TDI= X-SA-Exim-Connect-IP: 67.3.205.90 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-DCC: XMission; sa07 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ***;Linux Containers X-Spam-Relay-Country: X-Spam-Timing: total 728 ms - load_scoreonly_sql: 0.06 (0.0%), signal_user_changed: 3.5 (0.5%), b_tie_ro: 2.5 (0.3%), parse: 0.82 (0.1%), extract_message_metadata: 12 (1.7%), get_uri_detail_list: 2.4 (0.3%), tests_pri_-1000: 6 (0.8%), tests_pri_-950: 1.29 (0.2%), tests_pri_-900: 1.05 (0.1%), tests_pri_-400: 35 (4.8%), check_bayes: 33 (4.6%), b_tokenize: 13 (1.8%), b_tok_get_all: 9 (1.2%), b_comp_prob: 3.2 (0.4%), b_tok_touch_all: 4.4 (0.6%), b_finish: 0.78 (0.1%), tests_pri_0: 662 (90.9%), tests_pri_500: 4.0 (0.5%), rewrite_mail: 0.00 (0.0%) Subject: [CFT][PATCH 04/10] fs: Add helper functions for permanently empty directories. X-SA-Exim-Version: 4.2.1 (built Wed, 24 Sep 2014 11:00:52 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) 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 To ensure it is safe to mount proc and sysfs I need to check if filesystems that are mounted on top of them are mounted on truly empty directories. Given that some directories can gain entries over time, knowing that a directory is empty right now is insufficient. Therefore add supporting infrastructure for permantently empty directories that proc and sysfs can use when they create mount points for filesystems and fs_fully_visible can use to test for permanently empty directories to ensure that nothing will be gained by mounting a fresh copy of proc or sysfs. Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman" --- fs/libfs.c | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/fs.h | 2 ++ 2 files changed, 98 insertions(+) diff --git a/fs/libfs.c b/fs/libfs.c index cb1fb4b9b637..02813592e121 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -1093,3 +1093,99 @@ simple_nosetlease(struct file *filp, long arg, struct file_lock **flp, return -EINVAL; } EXPORT_SYMBOL(simple_nosetlease); + + +/* + * Operations for a permanently empty directory. + */ +static struct dentry *empty_dir_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags) +{ + return ERR_PTR(-ENOENT); +} + +static int empty_dir_getattr(struct vfsmount *mnt, struct dentry *dentry, + struct kstat *stat) +{ + struct inode *inode = d_inode(dentry); + generic_fillattr(inode, stat); + return 0; +} + +static int empty_dir_setattr(struct dentry *dentry, struct iattr *attr) +{ + return -EPERM; +} + +static int empty_dir_setxattr(struct dentry *dentry, const char *name, + const void *value, size_t size, int flags) +{ + return -EOPNOTSUPP; +} + +static ssize_t empty_dir_getxattr(struct dentry *dentry, const char *name, + void *value, size_t size) +{ + return -EOPNOTSUPP; +} + +static int empty_dir_removexattr(struct dentry *dentry, const char *name) +{ + return -EOPNOTSUPP; +} + +static ssize_t empty_dir_listxattr(struct dentry *dentry, char *list, size_t size) +{ + return -EOPNOTSUPP; +} + +static const struct inode_operations empty_dir_inode_operations = { + .lookup = empty_dir_lookup, + .permission = generic_permission, + .setattr = empty_dir_setattr, + .getattr = empty_dir_getattr, + .setxattr = empty_dir_setxattr, + .getxattr = empty_dir_getxattr, + .removexattr = empty_dir_removexattr, + .listxattr = empty_dir_listxattr, +}; + +static loff_t empty_dir_llseek(struct file *file, loff_t offset, int whence) +{ + /* An empty directory has two entries . and .. at offsets 0 and 1 */ + return generic_file_llseek_size(file, offset, whence, 2, 2); +} + +static int empty_dir_readdir(struct file *file, struct dir_context *ctx) +{ + dir_emit_dots(file, ctx); + return 0; +} + +static const struct file_operations empty_dir_operations = { + .llseek = empty_dir_llseek, + .read = generic_read_dir, + .iterate = empty_dir_readdir, + .fsync = noop_fsync, +}; + + +void make_empty_dir_inode(struct inode *inode) +{ + set_nlink(inode, 2); + inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO; + inode->i_uid = GLOBAL_ROOT_UID; + inode->i_gid = GLOBAL_ROOT_GID; + inode->i_rdev = 0; + inode->i_size = 2; + inode->i_blkbits = PAGE_SHIFT; + inode->i_blocks = 0; + + inode->i_op = &empty_dir_inode_operations; + inode->i_fop = &empty_dir_operations; +} + +bool is_empty_dir_inode(struct inode *inode) +{ + return (inode->i_fop == &empty_dir_operations) && + (inode->i_op == &empty_dir_inode_operations); +} diff --git a/include/linux/fs.h b/include/linux/fs.h index 2d24eeb8e59c..571aab91bfc0 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2780,6 +2780,8 @@ extern struct dentry *simple_lookup(struct inode *, struct dentry *, unsigned in extern ssize_t generic_read_dir(struct file *, char __user *, size_t, loff_t *); extern const struct file_operations simple_dir_operations; extern const struct inode_operations simple_dir_inode_operations; +extern void make_empty_dir_inode(struct inode *inode); +extern bool is_empty_dir_inode(struct inode *inode); struct tree_descr { char *name; const struct file_operations *ops; int mode; }; struct dentry *d_alloc_name(struct dentry *, const char *); extern int simple_fill_super(struct super_block *, unsigned long, struct tree_descr *);