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Registered in England and Wales under Company Registration No. 3798903 Subject: [RFC PATCH 08/27] containers, vfs: Honour CONTAINER_NEW_EMPTY_FS_NS From: David Howells To: keyrings@vger.kernel.org, trond.myklebust@hammerspace.com, sfrench@samba.org Cc: linux-security-module@vger.kernel.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, linux-fsdevel@vger.kernel.org, rgb@redhat.com, dhowells@redhat.com, linux-kernel@vger.kernel.org Date: Fri, 15 Feb 2019 16:08:29 +0000 Message-ID: <155024690964.21651.13823458384398366556.stgit@warthog.procyon.org.uk> In-Reply-To: <155024683432.21651.14153938339749694146.stgit@warthog.procyon.org.uk> References: <155024683432.21651.14153938339749694146.stgit@warthog.procyon.org.uk> User-Agent: StGit/unknown-version MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Fri, 15 Feb 2019 16:08:41 +0000 (UTC) Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org Allow a container to be created with an empty mount namespace, as specified by passing CONTAINER_NEW_EMPTY_FS_NS to container_create(), and allow a root filesystem to be mounted into the container: cfd = container_create("foo", CONTAINER_NEW_EMPTY_FS_NS); fsfd = fsopen("ext3", 0); fsconfig(fsfd, FSCONFIG_SET_CONTAINER, NULL, NULL, cfd); fsconfig(fsfd, FSCONFIG_SET_STRING, "source", "/dev/sda3", 0); fsconfig(fsfd, FSCONFIG_SET_FLAG, "user_xattr", NULL, 0); fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0); ... rfd = fsmount(fsfd, 0, 0); move_mount(rfd, "", cfd, "/", MOVE_MOUNT_F_EMPTY_PATH | MOVE_MOUNT_T_CONTAINER_ROOT); pfd = fsopen("proc", 0); write(pfd, "n c="); ... procfd = fsmount(pfd, 0, 0); move_mount(procfd, "", cfd, "proc", MOVE_MOUNT_F_EMPTY_PATH); Signed-off-by: David Howells --- fs/namespace.c | 95 +++++++++++++++++++++++++++++++++++++++----- include/uapi/linux/mount.h | 3 + kernel/container.c | 6 +++ kernel/fork.c | 6 ++- 4 files changed, 97 insertions(+), 13 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index cc5d56f7ae29..22cf4a8f8065 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3513,6 +3513,63 @@ SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags, return ret; } +/* + * Create a mount namespace for a container and set the root mount in it. + */ +static int set_container_root(struct path *path, int fd) +{ + struct mnt_namespace *mnt_ns; + struct container *container; + struct mount *mnt; + struct fd f; + int ret; + + f = fdget(fd); + if (!f.file) + return -EBADF; + ret = -EINVAL; + if (!is_container_file(f.file)) + goto out_fd; + + ret = -EBUSY; + container = f.file->private_data; + if (container->ns->mnt_ns) + goto out_fd; + + mnt_ns = alloc_mnt_ns(container->cred->user_ns, false); + if (IS_ERR(mnt_ns)) { + ret = PTR_ERR(mnt_ns); + goto out_fd; + } + + mnt = real_mount(path->mnt); + mnt_add_count(mnt, 1); + mnt->mnt_ns = mnt_ns; + mnt_ns->root = mnt; + mnt_ns->mounts++; + list_add(&mnt->mnt_list, &mnt_ns->list); + + ret = -EBUSY; + spin_lock(&container->lock); + if (!container->ns->mnt_ns) { + container->ns->mnt_ns = mnt_ns; + write_seqcount_begin(&container->seq); + container->root.mnt = path->mnt; + container->root.dentry = path->dentry; + write_seqcount_end(&container->seq); + path_get(&container->root); + mnt_ns = NULL; + ret = 0; + } + spin_unlock(&container->lock); + + if (ret < 0) + put_mnt_ns(mnt_ns); +out_fd: + fdput(f); + return ret; +} + /* * Move a mount from one place to another. In combination with * fsopen()/fsmount() this is used to install a new mount and in combination @@ -3528,6 +3585,7 @@ SYSCALL_DEFINE5(move_mount, { struct path from_path, to_path; unsigned int lflags; + char buf[2]; int ret = 0; if (!may_mount()) @@ -3536,6 +3594,17 @@ SYSCALL_DEFINE5(move_mount, if (flags & ~MOVE_MOUNT__MASK) return -EINVAL; + if (flags & MOVE_MOUNT_T_CONTAINER_ROOT) { + if (flags & (MOVE_MOUNT_T_SYMLINKS | + MOVE_MOUNT_T_AUTOMOUNTS | + MOVE_MOUNT_T_EMPTY_PATH)) + return -EINVAL; + if (strncpy_from_user(buf, to_pathname, 2) < 0) + return -EFAULT; + if (buf[0] != '/' || buf[1] != '\0') + return -EINVAL; + } + /* If someone gives a pathname, they aren't permitted to move * from an fd that requires unmount as we can't get at the flag * to clear it afterwards. @@ -3549,20 +3618,24 @@ SYSCALL_DEFINE5(move_mount, if (ret < 0) return ret; - lflags = 0; - if (flags & MOVE_MOUNT_T_SYMLINKS) lflags |= LOOKUP_FOLLOW; - if (flags & MOVE_MOUNT_T_AUTOMOUNTS) lflags |= LOOKUP_AUTOMOUNT; - if (flags & MOVE_MOUNT_T_EMPTY_PATH) lflags |= LOOKUP_EMPTY; + if (flags & MOVE_MOUNT_T_CONTAINER_ROOT) { + ret = set_container_root(&from_path, to_dfd); + } else { + lflags = 0; + if (flags & MOVE_MOUNT_T_SYMLINKS) lflags |= LOOKUP_FOLLOW; + if (flags & MOVE_MOUNT_T_AUTOMOUNTS) lflags |= LOOKUP_AUTOMOUNT; + if (flags & MOVE_MOUNT_T_EMPTY_PATH) lflags |= LOOKUP_EMPTY; - ret = user_path_at(to_dfd, to_pathname, lflags, &to_path); - if (ret < 0) - goto out_from; + ret = user_path_at(to_dfd, to_pathname, lflags, &to_path); + if (ret < 0) + goto out_from; - ret = security_move_mount(&from_path, &to_path); - if (ret < 0) - goto out_to; + ret = security_move_mount(&from_path, &to_path); + if (ret < 0) + goto out_to; - ret = do_move_mount(&from_path, &to_path); + ret = do_move_mount(&from_path, &to_path); + } out_to: path_put(&to_path); diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h index f60bbe6f4099..cfaa75fa0594 100644 --- a/include/uapi/linux/mount.h +++ b/include/uapi/linux/mount.h @@ -70,7 +70,8 @@ #define MOVE_MOUNT_T_SYMLINKS 0x00000010 /* Follow symlinks on to path */ #define MOVE_MOUNT_T_AUTOMOUNTS 0x00000020 /* Follow automounts on to path */ #define MOVE_MOUNT_T_EMPTY_PATH 0x00000040 /* Empty to path permitted */ -#define MOVE_MOUNT__MASK 0x00000077 +#define MOVE_MOUNT_T_CONTAINER_ROOT 0x00000080 /* Set as container root */ +#define MOVE_MOUNT__MASK 0x000000f7 /* * fsopen() flags. diff --git a/kernel/container.c b/kernel/container.c index fd3b2a6849a1..360284db959b 100644 --- a/kernel/container.c +++ b/kernel/container.c @@ -21,6 +21,7 @@ #include #include #include +#include #include "namespaces.h" struct container init_container = { @@ -400,6 +401,11 @@ static struct container *create_container(const char __user *name, unsigned int fs->root.mnt = NULL; fs->root.dentry = NULL; + if (flags & CONTAINER_NEW_EMPTY_FS_NS) { + put_mnt_ns(ns->mnt_ns); + ns->mnt_ns = NULL; + } + ret = security_container_alloc(c, flags); if (ret < 0) goto err_fs; diff --git a/kernel/fork.c b/kernel/fork.c index 09de5f35d312..6ec507a5f739 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2374,7 +2374,11 @@ SYSCALL_DEFINE1(fork_into_container, int, containerfd) if (is_container_file(f.file)) { struct container *dest_container = f.file->private_data; - ret = _do_fork(SIGCHLD, 0, 0, NULL, NULL, 0, dest_container); + if (!dest_container->ns->mnt_ns) + ret = -ENOENT; + else + ret = _do_fork(SIGCHLD, 0, 0, NULL, NULL, 0, + dest_container); } fdput(f); return ret;