From: Christian Brauner <christian.brauner@ubuntu.com> To: Alexander Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@infradead.org>, linux-fsdevel@vger.kernel.org Cc: Andy Lutomirski <luto@kernel.org>, Mimi Zohar <zohar@linux.ibm.com>, James Bottomley <James.Bottomley@hansenpartnership.com>, Andreas Dilger <adilger.kernel@dilger.ca>, containers@lists.linux-foundation.org, Christoph Hellwig <hch@lst.de>, Tycho Andersen <tycho@tycho.ws>, Paul Moore <paul@paul-moore.com>, Jonathan Corbet <corbet@lwn.net>, smbarber@chromium.org, linux-ext4@vger.kernel.org, Mrunal Patel <mpatel@redhat.com>, Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>, selinux@vger.kernel.org, Josh Triplett <josh@joshtriplett.org>, Seth Forshee <seth.forshee@canonical.com>, Aleksa Sarai <cyphar@cyphar.com>, Lennart Poettering <lennart@poettering.net>, OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>, Geoffrey Thomas <geofft@ldpreload.com>, David Howells <dhowells@redhat.com>, John Johansen <john.johansen@canonical.com>, Theodore Tso <tytso@mit.edu>, Dmitry Kasatkin <dmitry.kasatkin@gmail.com>, Stephen Smalley <stephen.smalley.work@gmail.com>, fstests@vger.kernel.org, linux-security-module@vger.kernel.org, "Eric W. Biederman" <ebiederm@xmission.com>, linux-api@vger.kernel.org, Casey Schaufler <casey@schaufler-ca.com>, Alban Crequy <alban@kinvolk.io>, linux-integrity@vger.kernel.org, Todd Kjos <tkjos@google.com> Subject: [PATCH v3 36/38] fs: introduce MOUNT_ATTR_IDMAP Date: Sat, 28 Nov 2020 22:35:25 +0100 [thread overview] Message-ID: <20201128213527.2669807-37-christian.brauner@ubuntu.com> (raw) In-Reply-To: <20201128213527.2669807-1-christian.brauner@ubuntu.com> Introduce a new mount bind mount property to allow idmapping mounts. The MOUNT_ATTR_IDMAP flag can be set via the new mount_setattr() syscall together with a file descriptor referring to a user namespace. The user namespace referenced by the namespace file descriptor will be attached to the bind mount. All interactions with the filesystem going through that mount will be idmapped according to the mapping specified in the user namespace attached to it. Using user namespaces to mark mounts means we can reuse all the existing infrastructure in the kernel that already exists to handle idmappings and can also use this for permission checking to allow unprivileged user to create idmapped mounts in the future. Idmapping a mount is decoupled from the caller's user and mount namespace. This means idmapped mounts can be created in the initial user namespace which is an important use-case for systemd-homed, portable usb-sticks between systems, sharing data between the initial user namespace and unprivileged containers, and other use-cases that have been brought up. For example, assume a home directory where all files are owned by uid and gid 1000 and the home directory is brought to a new laptop where the user has id 12345. The system administrator can simply create a mount of this home directory with a mapping of 1000:12345:1 and other mappings to indicate the ids should be kept. (With this it is e.g. also possible to create idmapped mounts on the host with an identity mapping 1:1:100000 where the root user is not mapped. A user with root access that e.g. has been pivot rooted into such a mount on the host will be not be able to execute, read, write, or create files as root.) Given that idmapping a mount is decoupled from the caller's user namespace a sufficiently privileged process such as a container manager can set up a shifted mount for the container and the container can simply pivot root to it. There's no need for the container to do anything. The mount will appear correctly mapped independent of the user namespace the container uses. This means we don't need to mark a mount as idmappable. In order to create an idmapped mount the caller must currently be privileged in the user namespace of the superblock the mount belongs to. Currently, once a mount has been idmapped we don't allow it to change its mapping. This can be changed in the future if the use-cases arise. Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Mauricio Vásquez Bernal <mauricio@kinvolk.io> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> --- /* v2 */ - Christoph Hellwig <hch@lst.de>: - Drop kconfig option to make vfs idmappings unconditional. - Move introduction of MOUNT_ATTR_IDMAP to the end of the series after all internal changes have been done. - Move MOUNT_ATTR_IDMAP handling from build_mount_kattr() to separate build_mount_idmapped() helper. - Move MNT_IDMAPPED handling from do_mount_setattr() into separate do_mount_idmap() helper. - Use more helpers instead of one big function for mount attribute changes. - Mauricio Vásquez Bernal <mauricio@kinvolk.io>: - Recalculate flags before checking can_change_locked_flags(). /* v3 */ - David Howells <dhowells@redhat.com>: - Use smp_load_acquire() and smp_store_release() in mnt_user_ns() and do_idmap_mount(). - Remove all references to MNT_IDMAPPED now that the flag has been removed. --- fs/internal.h | 1 + fs/namespace.c | 126 +++++++++++++++++++++++++++++++++++-- fs/proc_namespace.c | 3 + include/linux/fs.h | 2 +- include/linux/mount.h | 3 +- include/uapi/linux/mount.h | 5 +- 6 files changed, 133 insertions(+), 7 deletions(-) diff --git a/fs/internal.h b/fs/internal.h index a5a6c470dc07..b0978274155f 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -88,6 +88,7 @@ struct mount_kattr { unsigned int propagation; unsigned int lookup_flags; bool recurse; + struct user_namespace *mnt_user_ns; }; extern struct vfsmount *lookup_mnt(const struct path *); diff --git a/fs/namespace.c b/fs/namespace.c index a1fda548c3af..a74559c8093c 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -25,6 +25,7 @@ #include <linux/proc_ns.h> #include <linux/magic.h> #include <linux/memblock.h> +#include <linux/proc_fs.h> #include <linux/task_work.h> #include <linux/sched/task.h> #include <uapi/linux/mount.h> @@ -3468,7 +3469,8 @@ static int build_attr_flags(unsigned int attr_flags, unsigned int *flags) MOUNT_ATTR_NODEV | MOUNT_ATTR_NOEXEC | MOUNT_ATTR__ATIME | - MOUNT_ATTR_NODIRATIME)) + MOUNT_ATTR_NODIRATIME | + MOUNT_ATTR_IDMAP)) return -EINVAL; if (attr_flags & MOUNT_ATTR_RDONLY) @@ -3508,6 +3510,14 @@ SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags, if ((flags & ~(FSMOUNT_CLOEXEC)) != 0) return -EINVAL; + if (attr_flags & ~(MOUNT_ATTR_RDONLY | + MOUNT_ATTR_NOSUID | + MOUNT_ATTR_NODEV | + MOUNT_ATTR_NOEXEC | + MOUNT_ATTR__ATIME | + MOUNT_ATTR_NODIRATIME)) + return -EINVAL; + ret = build_attr_flags(attr_flags, &mnt_flags); if (ret) return ret; @@ -3830,6 +3840,32 @@ static unsigned int recalc_flags(struct mount_kattr *kattr, struct mount *mnt) return flags; } +static int can_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt) +{ + struct vfsmount *m = &mnt->mnt; + + if (!kattr->mnt_user_ns) + return 0; + + /* + * Once a mount has been idmapped we don't allow it to change its + * mapping. It makes things simpler and callers can just create + * another bind-mount they can idmap if they want to. + */ + if (mnt_user_ns(m) != &init_user_ns) + return -EPERM; + + /* The underlying filesystem doesn't support idmapped mounts yet. */ + if (!(m->mnt_sb->s_type->fs_flags & FS_ALLOW_IDMAP)) + return -EINVAL; + + /* We're controlling the superblock. */ + if (!ns_capable(m->mnt_sb->s_user_ns, CAP_SYS_ADMIN)) + return -EPERM; + + return 0; +} + static struct mount *mount_setattr_prepare(struct mount_kattr *kattr, struct mount *mnt, int *err) { @@ -3854,6 +3890,10 @@ static struct mount *mount_setattr_prepare(struct mount_kattr *kattr, goto out; } + *err = can_idmap_mount(kattr, m); + if (*err) + goto out; + last = m; if ((kattr->attr_set & MNT_READONLY) && @@ -3868,6 +3908,18 @@ static struct mount *mount_setattr_prepare(struct mount_kattr *kattr, return last; } +static void do_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt) +{ + struct user_namespace *user_ns; + + if (!kattr->mnt_user_ns) + return; + + user_ns = get_user_ns(kattr->mnt_user_ns); + /* Pairs with smp_load_acquire() in mnt_user_ns(). */ + smp_store_release(&mnt->mnt.mnt_user_ns, user_ns); +} + static void mount_setattr_commit(struct mount_kattr *kattr, struct mount *mnt, struct mount *last, int err) { @@ -3877,6 +3929,7 @@ static void mount_setattr_commit(struct mount_kattr *kattr, struct mount *mnt, if (!err) { unsigned int flags; + do_idmap_mount(kattr, m); flags = recalc_flags(kattr, m); WRITE_ONCE(m->mnt.mnt_flags, flags); } @@ -3949,7 +4002,65 @@ static int do_mount_setattr(struct path *path, struct mount_kattr *kattr) return err; } -static int build_mount_kattr(const struct mount_attr *attr, +static int build_mount_idmapped(const struct mount_attr *attr, size_t usize, + struct mount_kattr *kattr, unsigned int flags) +{ + int err = 0; + struct ns_common *ns; + struct user_namespace *user_ns; + struct file *file; + + if (!((attr->attr_set | attr->attr_clr) & MOUNT_ATTR_IDMAP)) + return 0; + + /* + * We currently do not support clearing an idmapped mount. If this ever + * is a use-case we can revisit this but for now let's keep it simple + * and not allow it. + */ + if (attr->attr_clr & MOUNT_ATTR_IDMAP) + return -EINVAL; + + if (usize < MOUNT_ATTR_SIZE_VER1) + return -EINVAL; + + if (attr->userns_fd > INT_MAX) + return -EINVAL; + + file = fget(attr->userns_fd); + if (!file) + return -EBADF; + + if (!proc_ns_file(file)) { + err = -EINVAL; + goto out_fput; + } + + ns = get_proc_ns(file_inode(file)); + if (ns->ops->type != CLONE_NEWUSER) { + err = -EINVAL; + goto out_fput; + } + + /* + * The init_user_ns is used to indicate that a vfsmount is not idmapped. + * This is simpler than just having to treat NULL as unmapped. Users + * wanting to idmap a mount to init_user_ns can just use a namespace + * with an identity mapping. + */ + user_ns = container_of(ns, struct user_namespace, ns); + if (user_ns == &init_user_ns) { + err = -EPERM; + goto out_fput; + } + kattr->mnt_user_ns = get_user_ns(user_ns); + +out_fput: + fput(file); + return err; +} + +static int build_mount_kattr(const struct mount_attr *attr, size_t usize, struct mount_kattr *kattr, unsigned int flags) { unsigned int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW; @@ -4028,7 +4139,13 @@ static int build_mount_kattr(const struct mount_attr *attr, } } - return 0; + return build_mount_idmapped(attr, usize, kattr, flags); +} + +static void finish_mount_kattr(struct mount_kattr *kattr) +{ + put_user_ns(kattr->mnt_user_ns); + kattr->mnt_user_ns = NULL; } SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path, unsigned int, flags, @@ -4060,7 +4177,7 @@ SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path, unsigned int if (attr.attr_set == 0 && attr.attr_clr == 0 && attr.propagation == 0) return 0; - err = build_mount_kattr(&attr, &kattr, flags); + err = build_mount_kattr(&attr, usize, &kattr, flags); if (err) return err; @@ -4069,6 +4186,7 @@ SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path, unsigned int return err; err = do_mount_setattr(&target, &kattr); + finish_mount_kattr(&kattr); path_put(&target); return err; } diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c index e59d4bb3a89e..71ab9497feb3 100644 --- a/fs/proc_namespace.c +++ b/fs/proc_namespace.c @@ -79,6 +79,9 @@ static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt) if (mnt->mnt_flags & fs_infop->flag) seq_puts(m, fs_infop->str); } + + if (mnt_user_ns(mnt) != &init_user_ns) + seq_puts(m, ",idmapped"); } static inline void mangle(struct seq_file *m, const char *s) diff --git a/include/linux/fs.h b/include/linux/fs.h index c7f9ba689145..b88ce1b2c87a 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2293,7 +2293,7 @@ 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_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 d0d4a270acea..f87811045aec 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -77,7 +77,8 @@ struct vfsmount { static inline struct user_namespace *mnt_user_ns(const struct vfsmount *mnt) { - return READ_ONCE(mnt->mnt_user_ns); + /* Pairs with smp_store_release() in do_idmap_mount(). */ + return smp_load_acquire(&mnt->mnt_user_ns); } struct file; /* forward dec */ diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h index fba42b4bfc1c..66422a58f061 100644 --- a/include/uapi/linux/mount.h +++ b/include/uapi/linux/mount.h @@ -119,6 +119,7 @@ enum fsconfig_command { #define MOUNT_ATTR_NOATIME 0x00000010 /* - Do not update access times. */ #define MOUNT_ATTR_STRICTATIME 0x00000020 /* - Always perform atime updates */ #define MOUNT_ATTR_NODIRATIME 0x00000080 /* Do not update directory access times */ +#define MOUNT_ATTR_IDMAP 0x00100000 /* Idmap this mount to @userns in mount_attr. */ /* * mount_setattr() @@ -127,6 +128,7 @@ struct mount_attr { __u64 attr_set; __u64 attr_clr; __u64 propagation; + __u64 userns_fd; }; /* Change propagation through mount_setattr(). */ @@ -140,6 +142,7 @@ enum propagation_type { /* List of all mount_attr versions. */ #define MOUNT_ATTR_SIZE_VER0 24 /* sizeof first published struct */ -#define MOUNT_ATTR_SIZE_LATEST MOUNT_ATTR_SIZE_VER0 +#define MOUNT_ATTR_SIZE_VER1 32 /* sizeof second published struct */ +#define MOUNT_ATTR_SIZE_LATEST MOUNT_ATTR_SIZE_VER1 #endif /* _UAPI_LINUX_MOUNT_H */ -- 2.29.2 _______________________________________________ Containers mailing list Containers@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/containers
WARNING: multiple messages have this Message-ID (diff)
From: Christian Brauner <christian.brauner@ubuntu.com> To: Alexander Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@infradead.org>, linux-fsdevel@vger.kernel.org Cc: "John Johansen" <john.johansen@canonical.com>, "James Morris" <jmorris@namei.org>, "Mimi Zohar" <zohar@linux.ibm.com>, "Dmitry Kasatkin" <dmitry.kasatkin@gmail.com>, "Stephen Smalley" <stephen.smalley.work@gmail.com>, "Casey Schaufler" <casey@schaufler-ca.com>, "Arnd Bergmann" <arnd@arndb.de>, "Andreas Dilger" <adilger.kernel@dilger.ca>, "OGAWA Hirofumi" <hirofumi@mail.parknet.co.jp>, "Geoffrey Thomas" <geofft@ldpreload.com>, "Mrunal Patel" <mpatel@redhat.com>, "Josh Triplett" <josh@joshtriplett.org>, "Andy Lutomirski" <luto@kernel.org>, "Theodore Tso" <tytso@mit.edu>, "Alban Crequy" <alban@kinvolk.io>, "Tycho Andersen" <tycho@tycho.ws>, "David Howells" <dhowells@redhat.com>, "James Bottomley" <James.Bottomley@hansenpartnership.com>, "Seth Forshee" <seth.forshee@canonical.com>, "Stéphane Graber" <stgraber@ubuntu.com>, "Aleksa Sarai" <cyphar@cyphar.com>, "Lennart Poettering" <lennart@poettering.net>, "Eric W. Biederman" <ebiederm@xmission.com>, smbarber@chromium.org, "Phil Estes" <estesp@gmail.com>, "Serge Hallyn" <serge@hallyn.com>, "Kees Cook" <keescook@chromium.org>, "Todd Kjos" <tkjos@google.com>, "Paul Moore" <paul@paul-moore.com>, "Jonathan Corbet" <corbet@lwn.net>, 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" <christian.brauner@ubuntu.com>, "Christoph Hellwig" <hch@lst.de>, "Mauricio Vásquez Bernal" <mauricio@kinvolk.io> Subject: [PATCH v3 36/38] fs: introduce MOUNT_ATTR_IDMAP Date: Sat, 28 Nov 2020 22:35:25 +0100 [thread overview] Message-ID: <20201128213527.2669807-37-christian.brauner@ubuntu.com> (raw) In-Reply-To: <20201128213527.2669807-1-christian.brauner@ubuntu.com> Introduce a new mount bind mount property to allow idmapping mounts. The MOUNT_ATTR_IDMAP flag can be set via the new mount_setattr() syscall together with a file descriptor referring to a user namespace. The user namespace referenced by the namespace file descriptor will be attached to the bind mount. All interactions with the filesystem going through that mount will be idmapped according to the mapping specified in the user namespace attached to it. Using user namespaces to mark mounts means we can reuse all the existing infrastructure in the kernel that already exists to handle idmappings and can also use this for permission checking to allow unprivileged user to create idmapped mounts in the future. Idmapping a mount is decoupled from the caller's user and mount namespace. This means idmapped mounts can be created in the initial user namespace which is an important use-case for systemd-homed, portable usb-sticks between systems, sharing data between the initial user namespace and unprivileged containers, and other use-cases that have been brought up. For example, assume a home directory where all files are owned by uid and gid 1000 and the home directory is brought to a new laptop where the user has id 12345. The system administrator can simply create a mount of this home directory with a mapping of 1000:12345:1 and other mappings to indicate the ids should be kept. (With this it is e.g. also possible to create idmapped mounts on the host with an identity mapping 1:1:100000 where the root user is not mapped. A user with root access that e.g. has been pivot rooted into such a mount on the host will be not be able to execute, read, write, or create files as root.) Given that idmapping a mount is decoupled from the caller's user namespace a sufficiently privileged process such as a container manager can set up a shifted mount for the container and the container can simply pivot root to it. There's no need for the container to do anything. The mount will appear correctly mapped independent of the user namespace the container uses. This means we don't need to mark a mount as idmappable. In order to create an idmapped mount the caller must currently be privileged in the user namespace of the superblock the mount belongs to. Currently, once a mount has been idmapped we don't allow it to change its mapping. This can be changed in the future if the use-cases arise. Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Mauricio Vásquez Bernal <mauricio@kinvolk.io> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> --- /* v2 */ - Christoph Hellwig <hch@lst.de>: - Drop kconfig option to make vfs idmappings unconditional. - Move introduction of MOUNT_ATTR_IDMAP to the end of the series after all internal changes have been done. - Move MOUNT_ATTR_IDMAP handling from build_mount_kattr() to separate build_mount_idmapped() helper. - Move MNT_IDMAPPED handling from do_mount_setattr() into separate do_mount_idmap() helper. - Use more helpers instead of one big function for mount attribute changes. - Mauricio Vásquez Bernal <mauricio@kinvolk.io>: - Recalculate flags before checking can_change_locked_flags(). /* v3 */ - David Howells <dhowells@redhat.com>: - Use smp_load_acquire() and smp_store_release() in mnt_user_ns() and do_idmap_mount(). - Remove all references to MNT_IDMAPPED now that the flag has been removed. --- fs/internal.h | 1 + fs/namespace.c | 126 +++++++++++++++++++++++++++++++++++-- fs/proc_namespace.c | 3 + include/linux/fs.h | 2 +- include/linux/mount.h | 3 +- include/uapi/linux/mount.h | 5 +- 6 files changed, 133 insertions(+), 7 deletions(-) diff --git a/fs/internal.h b/fs/internal.h index a5a6c470dc07..b0978274155f 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -88,6 +88,7 @@ struct mount_kattr { unsigned int propagation; unsigned int lookup_flags; bool recurse; + struct user_namespace *mnt_user_ns; }; extern struct vfsmount *lookup_mnt(const struct path *); diff --git a/fs/namespace.c b/fs/namespace.c index a1fda548c3af..a74559c8093c 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -25,6 +25,7 @@ #include <linux/proc_ns.h> #include <linux/magic.h> #include <linux/memblock.h> +#include <linux/proc_fs.h> #include <linux/task_work.h> #include <linux/sched/task.h> #include <uapi/linux/mount.h> @@ -3468,7 +3469,8 @@ static int build_attr_flags(unsigned int attr_flags, unsigned int *flags) MOUNT_ATTR_NODEV | MOUNT_ATTR_NOEXEC | MOUNT_ATTR__ATIME | - MOUNT_ATTR_NODIRATIME)) + MOUNT_ATTR_NODIRATIME | + MOUNT_ATTR_IDMAP)) return -EINVAL; if (attr_flags & MOUNT_ATTR_RDONLY) @@ -3508,6 +3510,14 @@ SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags, if ((flags & ~(FSMOUNT_CLOEXEC)) != 0) return -EINVAL; + if (attr_flags & ~(MOUNT_ATTR_RDONLY | + MOUNT_ATTR_NOSUID | + MOUNT_ATTR_NODEV | + MOUNT_ATTR_NOEXEC | + MOUNT_ATTR__ATIME | + MOUNT_ATTR_NODIRATIME)) + return -EINVAL; + ret = build_attr_flags(attr_flags, &mnt_flags); if (ret) return ret; @@ -3830,6 +3840,32 @@ static unsigned int recalc_flags(struct mount_kattr *kattr, struct mount *mnt) return flags; } +static int can_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt) +{ + struct vfsmount *m = &mnt->mnt; + + if (!kattr->mnt_user_ns) + return 0; + + /* + * Once a mount has been idmapped we don't allow it to change its + * mapping. It makes things simpler and callers can just create + * another bind-mount they can idmap if they want to. + */ + if (mnt_user_ns(m) != &init_user_ns) + return -EPERM; + + /* The underlying filesystem doesn't support idmapped mounts yet. */ + if (!(m->mnt_sb->s_type->fs_flags & FS_ALLOW_IDMAP)) + return -EINVAL; + + /* We're controlling the superblock. */ + if (!ns_capable(m->mnt_sb->s_user_ns, CAP_SYS_ADMIN)) + return -EPERM; + + return 0; +} + static struct mount *mount_setattr_prepare(struct mount_kattr *kattr, struct mount *mnt, int *err) { @@ -3854,6 +3890,10 @@ static struct mount *mount_setattr_prepare(struct mount_kattr *kattr, goto out; } + *err = can_idmap_mount(kattr, m); + if (*err) + goto out; + last = m; if ((kattr->attr_set & MNT_READONLY) && @@ -3868,6 +3908,18 @@ static struct mount *mount_setattr_prepare(struct mount_kattr *kattr, return last; } +static void do_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt) +{ + struct user_namespace *user_ns; + + if (!kattr->mnt_user_ns) + return; + + user_ns = get_user_ns(kattr->mnt_user_ns); + /* Pairs with smp_load_acquire() in mnt_user_ns(). */ + smp_store_release(&mnt->mnt.mnt_user_ns, user_ns); +} + static void mount_setattr_commit(struct mount_kattr *kattr, struct mount *mnt, struct mount *last, int err) { @@ -3877,6 +3929,7 @@ static void mount_setattr_commit(struct mount_kattr *kattr, struct mount *mnt, if (!err) { unsigned int flags; + do_idmap_mount(kattr, m); flags = recalc_flags(kattr, m); WRITE_ONCE(m->mnt.mnt_flags, flags); } @@ -3949,7 +4002,65 @@ static int do_mount_setattr(struct path *path, struct mount_kattr *kattr) return err; } -static int build_mount_kattr(const struct mount_attr *attr, +static int build_mount_idmapped(const struct mount_attr *attr, size_t usize, + struct mount_kattr *kattr, unsigned int flags) +{ + int err = 0; + struct ns_common *ns; + struct user_namespace *user_ns; + struct file *file; + + if (!((attr->attr_set | attr->attr_clr) & MOUNT_ATTR_IDMAP)) + return 0; + + /* + * We currently do not support clearing an idmapped mount. If this ever + * is a use-case we can revisit this but for now let's keep it simple + * and not allow it. + */ + if (attr->attr_clr & MOUNT_ATTR_IDMAP) + return -EINVAL; + + if (usize < MOUNT_ATTR_SIZE_VER1) + return -EINVAL; + + if (attr->userns_fd > INT_MAX) + return -EINVAL; + + file = fget(attr->userns_fd); + if (!file) + return -EBADF; + + if (!proc_ns_file(file)) { + err = -EINVAL; + goto out_fput; + } + + ns = get_proc_ns(file_inode(file)); + if (ns->ops->type != CLONE_NEWUSER) { + err = -EINVAL; + goto out_fput; + } + + /* + * The init_user_ns is used to indicate that a vfsmount is not idmapped. + * This is simpler than just having to treat NULL as unmapped. Users + * wanting to idmap a mount to init_user_ns can just use a namespace + * with an identity mapping. + */ + user_ns = container_of(ns, struct user_namespace, ns); + if (user_ns == &init_user_ns) { + err = -EPERM; + goto out_fput; + } + kattr->mnt_user_ns = get_user_ns(user_ns); + +out_fput: + fput(file); + return err; +} + +static int build_mount_kattr(const struct mount_attr *attr, size_t usize, struct mount_kattr *kattr, unsigned int flags) { unsigned int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW; @@ -4028,7 +4139,13 @@ static int build_mount_kattr(const struct mount_attr *attr, } } - return 0; + return build_mount_idmapped(attr, usize, kattr, flags); +} + +static void finish_mount_kattr(struct mount_kattr *kattr) +{ + put_user_ns(kattr->mnt_user_ns); + kattr->mnt_user_ns = NULL; } SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path, unsigned int, flags, @@ -4060,7 +4177,7 @@ SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path, unsigned int if (attr.attr_set == 0 && attr.attr_clr == 0 && attr.propagation == 0) return 0; - err = build_mount_kattr(&attr, &kattr, flags); + err = build_mount_kattr(&attr, usize, &kattr, flags); if (err) return err; @@ -4069,6 +4186,7 @@ SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path, unsigned int return err; err = do_mount_setattr(&target, &kattr); + finish_mount_kattr(&kattr); path_put(&target); return err; } diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c index e59d4bb3a89e..71ab9497feb3 100644 --- a/fs/proc_namespace.c +++ b/fs/proc_namespace.c @@ -79,6 +79,9 @@ static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt) if (mnt->mnt_flags & fs_infop->flag) seq_puts(m, fs_infop->str); } + + if (mnt_user_ns(mnt) != &init_user_ns) + seq_puts(m, ",idmapped"); } static inline void mangle(struct seq_file *m, const char *s) diff --git a/include/linux/fs.h b/include/linux/fs.h index c7f9ba689145..b88ce1b2c87a 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2293,7 +2293,7 @@ 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_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 d0d4a270acea..f87811045aec 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -77,7 +77,8 @@ struct vfsmount { static inline struct user_namespace *mnt_user_ns(const struct vfsmount *mnt) { - return READ_ONCE(mnt->mnt_user_ns); + /* Pairs with smp_store_release() in do_idmap_mount(). */ + return smp_load_acquire(&mnt->mnt_user_ns); } struct file; /* forward dec */ diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h index fba42b4bfc1c..66422a58f061 100644 --- a/include/uapi/linux/mount.h +++ b/include/uapi/linux/mount.h @@ -119,6 +119,7 @@ enum fsconfig_command { #define MOUNT_ATTR_NOATIME 0x00000010 /* - Do not update access times. */ #define MOUNT_ATTR_STRICTATIME 0x00000020 /* - Always perform atime updates */ #define MOUNT_ATTR_NODIRATIME 0x00000080 /* Do not update directory access times */ +#define MOUNT_ATTR_IDMAP 0x00100000 /* Idmap this mount to @userns in mount_attr. */ /* * mount_setattr() @@ -127,6 +128,7 @@ struct mount_attr { __u64 attr_set; __u64 attr_clr; __u64 propagation; + __u64 userns_fd; }; /* Change propagation through mount_setattr(). */ @@ -140,6 +142,7 @@ enum propagation_type { /* List of all mount_attr versions. */ #define MOUNT_ATTR_SIZE_VER0 24 /* sizeof first published struct */ -#define MOUNT_ATTR_SIZE_LATEST MOUNT_ATTR_SIZE_VER0 +#define MOUNT_ATTR_SIZE_VER1 32 /* sizeof second published struct */ +#define MOUNT_ATTR_SIZE_LATEST MOUNT_ATTR_SIZE_VER1 #endif /* _UAPI_LINUX_MOUNT_H */ -- 2.29.2
next prev parent reply other threads:[~2020-11-28 21:51 UTC|newest] Thread overview: 150+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-11-28 21:34 [PATCH v3 00/38] idmapped mounts Christian Brauner 2020-11-28 21:34 ` Christian Brauner 2020-11-28 21:34 ` [PATCH v3 01/38] namespace: take lock_mount_hash() directly when changing flags Christian Brauner 2020-11-28 21:34 ` Christian Brauner 2020-12-01 10:31 ` Christoph Hellwig 2020-12-01 10:31 ` Christoph Hellwig 2020-12-02 9:09 ` Christian Brauner 2020-12-02 9:09 ` Christian Brauner 2020-11-28 21:34 ` [PATCH v3 02/38] mount: make {lock,unlock}_mount_hash() static Christian Brauner 2020-11-28 21:34 ` Christian Brauner 2020-12-01 10:32 ` Christoph Hellwig 2020-12-01 10:32 ` Christoph Hellwig 2020-12-02 9:11 ` Christian Brauner 2020-12-02 9:11 ` Christian Brauner 2020-11-28 21:34 ` [PATCH v3 03/38] namespace: only take read lock in do_reconfigure_mnt() Christian Brauner 2020-11-28 21:34 ` Christian Brauner 2020-12-01 10:32 ` Christoph Hellwig 2020-12-01 10:32 ` Christoph Hellwig 2020-12-02 9:14 ` Christian Brauner 2020-12-02 9:14 ` Christian Brauner 2020-11-28 21:34 ` [PATCH v3 04/38] fs: add mount_setattr() Christian Brauner 2020-11-28 21:34 ` Christian Brauner 2020-12-01 10:49 ` Christoph Hellwig 2020-12-01 10:49 ` Christoph Hellwig 2020-12-02 9:42 ` Christian Brauner 2020-12-02 9:42 ` Christian Brauner 2020-12-02 9:47 ` Christoph Hellwig 2020-12-02 9:47 ` Christoph Hellwig 2020-12-02 9:55 ` Christoph Hellwig 2020-12-02 9:55 ` Christoph Hellwig 2020-12-02 9:57 ` Christian Brauner 2020-12-02 9:57 ` Christian Brauner 2020-12-02 10:01 ` Christoph Hellwig 2020-12-02 10:01 ` Christoph Hellwig 2020-11-28 21:34 ` [PATCH v3 05/38] tests: add mount_setattr() selftests Christian Brauner 2020-11-28 21:34 ` Christian Brauner 2020-11-28 21:34 ` [PATCH v3 06/38] fs: add id translation helpers Christian Brauner 2020-11-28 21:34 ` Christian Brauner 2020-12-01 10:49 ` Christoph Hellwig 2020-12-01 10:49 ` Christoph Hellwig 2020-12-02 9:16 ` Christian Brauner 2020-12-02 9:16 ` Christian Brauner 2020-11-28 21:34 ` [PATCH v3 07/38] mount: attach mappings to mounts Christian Brauner 2020-11-28 21:34 ` Christian Brauner 2020-12-01 10:50 ` Christoph Hellwig 2020-12-01 10:50 ` Christoph Hellwig 2020-12-01 13:25 ` Tycho Andersen 2020-12-01 13:25 ` Tycho Andersen 2020-12-02 9:24 ` Christian Brauner 2020-12-02 9:24 ` Christian Brauner 2020-11-28 21:34 ` [PATCH v3 08/38] capability: handle idmapped mounts Christian Brauner 2020-11-28 21:34 ` Christian Brauner 2020-11-28 22:34 ` Serge E. Hallyn 2020-11-28 22:34 ` Serge E. Hallyn 2020-11-28 21:34 ` [PATCH v3 09/38] namei: add idmapped mount aware permission helpers Christian Brauner 2020-11-28 21:34 ` Christian Brauner 2020-11-28 22:47 ` Serge E. Hallyn 2020-11-28 22:47 ` Serge E. Hallyn 2020-12-01 10:58 ` Christian Brauner 2020-12-01 10:58 ` Christian Brauner 2020-12-01 10:51 ` Christoph Hellwig 2020-12-01 10:51 ` Christoph Hellwig 2020-12-01 10:58 ` Christian Brauner 2020-12-01 10:58 ` Christian Brauner 2020-11-28 21:34 ` [PATCH v3 10/38] inode: add idmapped mount aware init and " Christian Brauner 2020-11-28 21:34 ` Christian Brauner 2020-12-01 10:51 ` Christoph Hellwig 2020-12-01 10:51 ` Christoph Hellwig 2020-12-02 9:17 ` Christian Brauner 2020-12-02 9:17 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 11/38] attr: handle idmapped mounts Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 12/38] acl: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 13/38] xattr: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 14/38] commoncap: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 15/38] stat: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 16/38] namei: handle idmapped mounts in may_*() helpers Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 17/38] namei: introduce struct renamedata Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-12-01 10:53 ` Christoph Hellwig 2020-12-01 10:53 ` Christoph Hellwig 2020-12-02 9:18 ` Christian Brauner 2020-12-02 9:18 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 18/38] namei: prepare for idmapped mounts Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 19/38] open: handle idmapped mounts in do_truncate() Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 20/38] open: handle idmapped mounts Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 21/38] af_unix: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 22/38] utimes: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 23/38] fcntl: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 24/38] notify: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 25/38] init: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 26/38] ioctl: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 27/38] would_dump: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 28/38] exec: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 29/38] fs: add helpers for idmap mounts Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 30/38] apparmor: handle idmapped mounts Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 31/38] ima: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 32/38] fat: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-30 22:50 ` Mauricio Vásquez Bernal 2020-11-30 22:50 ` Mauricio Vásquez Bernal 2020-12-01 10:24 ` Christian Brauner 2020-12-01 10:24 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 33/38] ext4: support " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-30 22:52 ` Mauricio Vásquez Bernal 2020-11-30 22:52 ` Mauricio Vásquez Bernal 2020-12-01 10:28 ` Christian Brauner 2020-12-01 10:28 ` Christian Brauner 2020-12-01 10:54 ` Christoph Hellwig 2020-12-01 10:54 ` Christoph Hellwig 2020-12-01 11:02 ` Christian Brauner 2020-12-01 11:02 ` Christian Brauner 2020-12-01 11:13 ` Christoph Hellwig 2020-12-01 11:13 ` Christoph Hellwig 2020-12-01 11:14 ` Christian Brauner 2020-12-01 11:14 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 34/38] ecryptfs: do not mount on top of " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 35/38] overlayfs: " Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` Christian Brauner [this message] 2020-11-28 21:35 ` [PATCH v3 36/38] fs: introduce MOUNT_ATTR_IDMAP Christian Brauner 2020-11-28 21:35 ` [PATCH v3 37/38] tests: extend mount_setattr tests Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 21:35 ` [PATCH v3 38/38] generic/618: add fstests for idmapped mounts Christian Brauner 2020-11-28 21:35 ` Christian Brauner 2020-11-28 22:54 ` [PATCH v3 00/38] " Serge E. Hallyn 2020-11-28 22:54 ` Serge E. Hallyn 2020-12-01 10:18 ` Christian Brauner 2020-12-01 10:18 ` Christian Brauner
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20201128213527.2669807-37-christian.brauner@ubuntu.com \ --to=christian.brauner@ubuntu.com \ --cc=James.Bottomley@hansenpartnership.com \ --cc=adilger.kernel@dilger.ca \ --cc=alban@kinvolk.io \ --cc=arnd@arndb.de \ --cc=casey@schaufler-ca.com \ --cc=containers@lists.linux-foundation.org \ --cc=corbet@lwn.net \ --cc=cyphar@cyphar.com \ --cc=dhowells@redhat.com \ --cc=dmitry.kasatkin@gmail.com \ --cc=ebiederm@xmission.com \ --cc=fstests@vger.kernel.org \ --cc=geofft@ldpreload.com \ --cc=hch@infradead.org \ --cc=hch@lst.de \ --cc=hirofumi@mail.parknet.co.jp \ --cc=john.johansen@canonical.com \ --cc=josh@joshtriplett.org \ --cc=keescook@chromium.org \ --cc=lennart@poettering.net \ --cc=linux-api@vger.kernel.org \ --cc=linux-ext4@vger.kernel.org \ --cc=linux-fsdevel@vger.kernel.org \ --cc=linux-integrity@vger.kernel.org \ --cc=linux-security-module@vger.kernel.org \ --cc=luto@kernel.org \ --cc=mpatel@redhat.com \ --cc=paul@paul-moore.com \ --cc=selinux@vger.kernel.org \ --cc=seth.forshee@canonical.com \ --cc=smbarber@chromium.org \ --cc=stephen.smalley.work@gmail.com \ --cc=tkjos@google.com \ --cc=tycho@tycho.ws \ --cc=tytso@mit.edu \ --cc=viro@zeniv.linux.org.uk \ --cc=zohar@linux.ibm.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.