From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2992826AbXDTK2u (ORCPT ); Fri, 20 Apr 2007 06:28:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1423043AbXDTK2Q (ORCPT ); Fri, 20 Apr 2007 06:28:16 -0400 Received: from mail-gw3.sa.ew.hu ([212.108.200.82]:56611 "EHLO mail-gw3.sa.ew.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423047AbXDTK2G (ORCPT ); Fri, 20 Apr 2007 06:28:06 -0400 Message-Id: <20070420102641.165244483@szeredi.hu> References: <20070420102532.385211890@szeredi.hu> User-Agent: quilt/0.45-1 Date: Fri, 20 Apr 2007 12:25:37 +0200 From: Miklos Szeredi To: akpm@linux-foundation.org, serue@us.ibm.com, viro@ftp.linux.org.uk, linuxram@us.ibm.com, ebiederm@xmission.com Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, containers@lists.osdl.org Subject: [patch 5/8] allow unprivileged bind mounts Content-Disposition: inline; filename=unprivileged_bind_mount.patch Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: Miklos Szeredi Allow bind mounts to unprivileged users if the following conditions are met: - mountpoint is not a symlink or special file - parent mount is owned by the user - the number of user mounts is below the maximum Unprivileged mounts imply MS_SETUSER, and will also have the "nosuid" and "nodev" mount flags set. Signed-off-by: Miklos Szeredi --- Index: linux/fs/namespace.c =================================================================== --- linux.orig/fs/namespace.c 2007-04-20 11:55:09.000000000 +0200 +++ linux/fs/namespace.c 2007-04-20 11:55:10.000000000 +0200 @@ -237,11 +237,30 @@ static void dec_nr_user_mounts(void) spin_unlock(&vfsmount_lock); } -static void set_mnt_user(struct vfsmount *mnt) +static int reserve_user_mount(void) +{ + int err = 0; + spin_lock(&vfsmount_lock); + if (nr_user_mounts >= max_user_mounts && !capable(CAP_SYS_ADMIN)) + err = -EPERM; + else + nr_user_mounts++; + spin_unlock(&vfsmount_lock); + return err; +} + +static void __set_mnt_user(struct vfsmount *mnt) { BUG_ON(mnt->mnt_flags & MNT_USER); mnt->mnt_uid = current->uid; mnt->mnt_flags |= MNT_USER; + if (!capable(CAP_SYS_ADMIN)) + mnt->mnt_flags |= MNT_NOSUID | MNT_NODEV; +} + +static void set_mnt_user(struct vfsmount *mnt) +{ + __set_mnt_user(mnt); spin_lock(&vfsmount_lock); nr_user_mounts++; spin_unlock(&vfsmount_lock); @@ -260,9 +279,16 @@ static struct vfsmount *clone_mnt(struct int flag) { struct super_block *sb = old->mnt_sb; - struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname); + struct vfsmount *mnt; + + if (flag & CL_SETUSER) { + int err = reserve_user_mount(); + if (err) + return ERR_PTR(err); + } + mnt = alloc_vfsmnt(old->mnt_devname); if (!mnt) - return ERR_PTR(-ENOMEM); + goto alloc_failed; mnt->mnt_flags = old->mnt_flags; atomic_inc(&sb->s_active); @@ -274,7 +300,7 @@ static struct vfsmount *clone_mnt(struct /* don't copy the MNT_USER flag */ mnt->mnt_flags &= ~MNT_USER; if (flag & CL_SETUSER) - set_mnt_user(mnt); + __set_mnt_user(mnt); if (flag & CL_SLAVE) { list_add(&mnt->mnt_slave, &old->mnt_slave_list); @@ -299,6 +325,11 @@ static struct vfsmount *clone_mnt(struct spin_unlock(&vfsmount_lock); } return mnt; + + alloc_failed: + if (flag & CL_SETUSER) + dec_nr_user_mounts(); + return ERR_PTR(-ENOMEM); } static inline void __mntput(struct vfsmount *mnt) @@ -745,22 +776,29 @@ asmlinkage long sys_oldumount(char __use #endif -static int mount_is_safe(struct nameidata *nd) +/* + * Conditions for unprivileged mounts are: + * - mountpoint is not a symlink or special file + * - mountpoint is in a mount owned by the user + */ +static bool permit_mount(struct nameidata *nd, int *flags) { + struct inode *inode = nd->dentry->d_inode; + if (capable(CAP_SYS_ADMIN)) - return 0; - return -EPERM; -#ifdef notyet - if (S_ISLNK(nd->dentry->d_inode->i_mode)) - return -EPERM; - if (nd->dentry->d_inode->i_mode & S_ISVTX) { - if (current->uid != nd->dentry->d_inode->i_uid) - return -EPERM; - } - if (vfs_permission(nd, MAY_WRITE)) - return -EPERM; - return 0; -#endif + return true; + + if (!S_ISDIR(inode->i_mode) && !S_ISREG(inode->i_mode)) + return false; + + if (!(nd->mnt->mnt_flags & MNT_USER)) + return false; + + if (nd->mnt->mnt_uid != current->uid) + return false; + + *flags |= MS_SETUSER; + return true; } static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry) @@ -981,9 +1019,10 @@ static int do_loopback(struct nameidata int clone_flags; struct nameidata old_nd; struct vfsmount *mnt = NULL; - int err = mount_is_safe(nd); - if (err) - return err; + int err; + + if (!permit_mount(nd, &flags)) + return -EPERM; if (!old_name || !*old_name) return -EINVAL; err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd); --