Each namespace has an owning user namespace and now there is not way to discover these relationships. Understending namespaces relationships allows to answer the question: what capability does process X have to perform operations on a resource governed by namespace Y? After a long discussion, Eric W. Biederman proposed to use ioctl-s for this purpose. The NS_GET_USERNS ioctl returns a file descriptor to an owning user namespace. It returns EPERM if a target namespace is outside of a current user namespace. Link: https://lkml.org/lkml/2016/7/6/158 Signed-off-by: Andrey Vagin <avagin@xxxxxxxxxx> --- fs/nsfs.c | 94 ++++++++++++++++++++++++++++++++++++++++------- include/uapi/linux/nsfs.h | 9 +++++ 2 files changed, 90 insertions(+), 13 deletions(-) create mode 100644 include/uapi/linux/nsfs.h diff --git a/fs/nsfs.c b/fs/nsfs.c index 8f20d60..1e5d2d0 100644 --- a/fs/nsfs.c +++ b/fs/nsfs.c @@ -5,11 +5,16 @@ #include <linux/magic.h> #include <linux/ktime.h> #include <linux/seq_file.h> +#include <linux/user_namespace.h> +#include <linux/nsfs.h> static struct vfsmount *nsfs_mnt; +static long ns_ioctl(struct file *filp, unsigned int ioctl, + unsigned long arg); static const struct file_operations ns_file_operations = { .llseek = no_llseek, + .unlocked_ioctl = ns_ioctl, }; static char *ns_dname(struct dentry *dentry, char *buffer, int buflen) @@ -44,22 +49,14 @@ static void nsfs_evict(struct inode *inode) ns->ops->put(ns); } -void *ns_get_path(struct path *path, struct task_struct *task, - const struct proc_ns_operations *ns_ops) +static void *__ns_get_path(struct path *path, struct ns_common *ns) { struct vfsmount *mnt = mntget(nsfs_mnt); struct qstr qname = { .name = "", }; struct dentry *dentry; struct inode *inode; - struct ns_common *ns; unsigned long d; -again: - ns = ns_ops->get(task); - if (!ns) { - mntput(mnt); - return ERR_PTR(-ENOENT); - } rcu_read_lock(); d = atomic_long_read(&ns->stashed); if (!d) @@ -68,7 +65,7 @@ again: if (!lockref_get_not_dead(&dentry->d_lockref)) goto slow; rcu_read_unlock(); - ns_ops->put(ns); + ns->ops->put(ns); got_it: path->mnt = mnt; path->dentry = dentry; @@ -77,7 +74,7 @@ slow: rcu_read_unlock(); inode = new_inode_pseudo(mnt->mnt_sb); if (!inode) { - ns_ops->put(ns); + ns->ops->put(ns); mntput(mnt); return ERR_PTR(-ENOMEM); } @@ -95,17 +92,88 @@ slow: return ERR_PTR(-ENOMEM); } d_instantiate(dentry, inode); - dentry->d_fsdata = (void *)ns_ops; + dentry->d_fsdata = (void *)ns->ops; d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry); if (d) { d_delete(dentry); /* make sure ->d_prune() does nothing */ dput(dentry); cpu_relax(); - goto again; + return ERR_PTR(-EAGAIN); } goto got_it; } +void *ns_get_path(struct path *path, struct task_struct *task, + const struct proc_ns_operations *ns_ops) +{ + struct ns_common *ns; + void *ret; + +again: + ns = ns_ops->get(task); + if (!ns) + return ERR_PTR(-ENOENT); + + ret = __ns_get_path(path, ns); + if (IS_ERR(ret) && PTR_ERR(ret) == -EAGAIN) + goto again; + return ret; +} + +int open_related_ns(struct ns_common *ns, + struct ns_common *(*get_ns)(struct ns_common *ns)) +{ + struct path path = {}; + struct file *f; + void *err; + int fd; + + fd = get_unused_fd_flags(O_CLOEXEC); + if (fd < 0) + return fd; + + while (1) { + struct ns_common *parent; + + parent = get_ns(ns); + if (IS_ERR(parent)) { + put_unused_fd(fd); + return PTR_ERR(parent); + } + + err = __ns_get_path(&path, parent); + if (IS_ERR(err) && PTR_ERR(err) == -EAGAIN) + continue; + break; + } + if (IS_ERR(err)) { + put_unused_fd(fd); + return PTR_ERR(err); + } + + f = dentry_open(&path, O_RDONLY, current_cred()); + path_put(&path); + if (IS_ERR(f)) { + put_unused_fd(fd); + fd = PTR_ERR(f); + } else + fd_install(fd, f); + return fd; +} + +static long ns_ioctl(struct file *filp, unsigned int ioctl, + unsigned long arg) +{ + struct ns_common *ns = get_proc_ns(file_inode(filp)); + + switch (ioctl) { + case NS_GET_USERNS: + return open_related_ns(ns, ns_get_owner); + default: + return -ENOTTY; + } +} + int ns_get_name(char *buf, size_t size, struct task_struct *task, const struct proc_ns_operations *ns_ops) { diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h new file mode 100644 index 0000000..7a09ede --- /dev/null +++ b/include/uapi/linux/nsfs.h @@ -0,0 +1,9 @@ +#ifndef __LINUX_NSFS_H +#define __LINUX_NSFS_H + +#include <linux/ioctl.h> + +#define NSIO 0xb7 +#define NS_GET_USERNS _IO(NSIO, 0x1) + +#endif /* __LINUX_NSFS_H */ -- 2.5.5 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
