From patchwork Sat Nov 28 21:34:56 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Brauner X-Patchwork-Id: 11938435 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 254461398 for ; Sat, 28 Nov 2020 22:25:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16779222C2 for ; Sat, 28 Nov 2020 22:25:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726865AbgK1WZM (ORCPT ); Sat, 28 Nov 2020 17:25:12 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:53682 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387833AbgK1Vqa (ORCPT ); Sat, 28 Nov 2020 16:46:30 -0500 Received: from ip5f5af0a0.dynamic.kabel-deutschland.de ([95.90.240.160] helo=wittgenstein.fritz.box) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1kj82K-0002aM-Pg; Sat, 28 Nov 2020 21:45:45 +0000 From: Christian Brauner To: Alexander Viro , Christoph Hellwig , linux-fsdevel@vger.kernel.org Cc: John Johansen , James Morris , Mimi Zohar , Dmitry Kasatkin , Stephen Smalley , Casey Schaufler , Arnd Bergmann , Andreas Dilger , OGAWA Hirofumi , Geoffrey Thomas , Mrunal Patel , Josh Triplett , Andy Lutomirski , Theodore Tso , Alban Crequy , Tycho Andersen , David Howells , James Bottomley , Seth Forshee , =?utf-8?q?St=C3=A9phane_Graber?= , Aleksa Sarai , Lennart Poettering , "Eric W. Biederman" , smbarber@chromium.org, Phil Estes , Serge Hallyn , Kees Cook , Todd Kjos , Paul Moore , Jonathan Corbet , containers@lists.linux-foundation.org, fstests@vger.kernel.org, linux-security-module@vger.kernel.org, linux-api@vger.kernel.org, linux-ext4@vger.kernel.org, linux-integrity@vger.kernel.org, selinux@vger.kernel.org, Christian Brauner , Christoph Hellwig Subject: [PATCH v3 07/38] mount: attach mappings to mounts Date: Sat, 28 Nov 2020 22:34:56 +0100 Message-Id: <20201128213527.2669807-8-christian.brauner@ubuntu.com> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201128213527.2669807-1-christian.brauner@ubuntu.com> References: <20201128213527.2669807-1-christian.brauner@ubuntu.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: fstests@vger.kernel.org In order to support per-mount idmappings vfsmounts will be marked with user namespaces. The idmapping associated with that user namespace will be used to map the ids of vfs objects when they are accessed through that mount. By default all vfsmounts are marked with the initial user namespace. The initial user namespace is used to indicate that a mount is not idmapped. All operations behave as before. Based on prior discussions we want to attach the whole user namespace and not just a dedicated idmapping struct. This allows us to reuse all the helpers that already exist for dealing with idmappings instead of introducing a whole new range of helpers. In addition, if we decide in the future that we are confident enough to enable unprivileged users to setup idmapped mounts we can allow already idmapped mounts to be marked with another user namespace. The permission checking would then take into account whether the caller is privileged in the user namespace the mount is currently marked with. For now, we will enforce in later patches that once a mount has been idmapped it can't be remapped. This keeps permission checking and life-cycle management simple, especially since users can always create a new mount with a different idmapping anyway. The idea to attach user namespaces to vfsmounts has been floated around in various forms at Linux Plumbers in ~2018 with the original idea tracing back to a discussion during a conference in St. Petersburg between Christoph, Tycho, and myself. Cc: Christoph Hellwig Cc: David Howells Cc: Al Viro Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner --- /* v2 */ patch introduced - Christoph Hellwig : - Split internal implementation into separate patch and move syscall implementation later. /* v3 */ - David Howells : - Remove MNT_IDMAPPED flag. We can simply check the pointer and use smp_load_acquire() in later patches. - Tycho Andersen : - Use READ_ONCE() in mnt_user_ns(). --- fs/namespace.c | 9 +++++++++ include/linux/fs.h | 1 + include/linux/mount.h | 6 ++++++ 3 files changed, 16 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index f9ea31b7eb7f..a1fda548c3af 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -220,6 +220,7 @@ static struct mount *alloc_vfsmnt(const char *name) INIT_HLIST_NODE(&mnt->mnt_mp_list); INIT_LIST_HEAD(&mnt->mnt_umounting); INIT_HLIST_HEAD(&mnt->mnt_stuck_children); + mnt->mnt.mnt_user_ns = &init_user_ns; } return mnt; @@ -559,6 +560,11 @@ int sb_prepare_remount_readonly(struct super_block *sb) static void free_vfsmnt(struct mount *mnt) { + struct user_namespace *ns; + + ns = mnt_user_ns(&mnt->mnt); + if (ns != &init_user_ns) + put_user_ns(ns); kfree_const(mnt->mnt_devname); #ifdef CONFIG_SMP free_percpu(mnt->mnt_pcp); @@ -1067,6 +1073,9 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root, mnt->mnt.mnt_flags &= ~(MNT_WRITE_HOLD|MNT_MARKED|MNT_INTERNAL); atomic_inc(&sb->s_active); + mnt->mnt.mnt_user_ns = mnt_user_ns(&old->mnt); + if (mnt->mnt.mnt_user_ns != &init_user_ns) + mnt->mnt.mnt_user_ns = get_user_ns(mnt->mnt.mnt_user_ns); mnt->mnt.mnt_sb = sb; mnt->mnt.mnt_root = dget(root); mnt->mnt_mountpoint = mnt->mnt.mnt_root; diff --git a/include/linux/fs.h b/include/linux/fs.h index f59b7f16f216..004686f49e32 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2276,6 +2276,7 @@ struct file_system_type { #define FS_HAS_SUBTYPE 4 #define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */ #define FS_DISALLOW_NOTIFY_PERM 16 /* Disable fanotify permission events */ +#define FS_ALLOW_IDMAP 32 /* FS has been updated to handle vfs idmappings. */ #define FS_THP_SUPPORT 8192 /* Remove once all fs converted */ #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */ int (*init_fs_context)(struct fs_context *); diff --git a/include/linux/mount.h b/include/linux/mount.h index aaf343b38671..d0d4a270acea 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -72,8 +72,14 @@ struct vfsmount { struct dentry *mnt_root; /* root of the mounted tree */ struct super_block *mnt_sb; /* pointer to superblock */ int mnt_flags; + struct user_namespace *mnt_user_ns; } __randomize_layout; +static inline struct user_namespace *mnt_user_ns(const struct vfsmount *mnt) +{ + return READ_ONCE(mnt->mnt_user_ns); +} + struct file; /* forward dec */ struct path;