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take the targets of /proc/*/ns/* symlinks to separate fs

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New pseudo-filesystem: nsfs.  Targets of /proc/*/ns/* live there now.
It's not mountable (not even registered, so it's not in /proc/filesystems,
etc.).  Files on it *are* bindable - we explicitly permit that in do_loopback().

This stuff lives in fs/nsfs.c now; proc_ns_fget() moved there as well.
get_proc_ns() is a macro now (it's simply returning ->i_private; would
have been an inline, if not for header ordering headache).
proc_ns_inode() is an ex-parrot.  The interface used in procfs is
ns_get_path(path, task, ops) and ns_get_name(buf, size, task, ops).

Dentries and inodes are never hashed; a non-counting reference to dentry
is stashed in ns_common (removed by ->d_prune()) and reused by ns_get_path()
if present.  See ns_get_path()/ns_prune_dentry/nsfs_evict() for details
of that mechanism.

As the result, proc_ns_follow_link() has stopped poking in nd->path.mnt;
it does nd_jump_link() on a consistent <vfsmount,dentry> pair it gets
from ns_get_path().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2014-11-01 10:57:28 -04:00
parent f77c80142e
commit e149ed2b80
10 changed files with 208 additions and 161 deletions
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31
include/linux/proc_ns.h
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@@ -4,9 +4,11 @@
#ifndef _LINUX_PROC_NS_H
#define _LINUX_PROC_NS_H
#include <linux/ns_common.h>
struct pid_namespace;
struct nsproxy;
struct ns_common;
struct path;
struct proc_ns_operations {
const char *name;
@@ -38,35 +40,38 @@ enum {
extern int pid_ns_prepare_proc(struct pid_namespace *ns);
extern void pid_ns_release_proc(struct pid_namespace *ns);
extern struct file *proc_ns_fget(int fd);
extern struct ns_common *get_proc_ns(struct inode *);
extern int proc_alloc_inum(unsigned int *pino);
extern void proc_free_inum(unsigned int inum);
extern bool proc_ns_inode(struct inode *inode);
#else /* CONFIG_PROC_FS */
static inline int pid_ns_prepare_proc(struct pid_namespace *ns) { return 0; }
static inline void pid_ns_release_proc(struct pid_namespace *ns) {}
static inline struct file *proc_ns_fget(int fd)
{
return ERR_PTR(-EINVAL);
}
static inline struct ns_common *get_proc_ns(struct inode *inode) { return NULL; }
static inline int proc_alloc_inum(unsigned int *inum)
{
*inum = 1;
return 0;
}
static inline void proc_free_inum(unsigned int inum) {}
static inline bool proc_ns_inode(struct inode *inode) { return false; }
#endif /* CONFIG_PROC_FS */
#define ns_alloc_inum(ns) proc_alloc_inum(&(ns)->inum)
static inline int ns_alloc_inum(struct ns_common *ns)
{
atomic_long_set(&ns->stashed, 0);
return proc_alloc_inum(&ns->inum);
}
#define ns_free_inum(ns) proc_free_inum((ns)->inum)
extern struct file *proc_ns_fget(int fd);
#define get_proc_ns(inode) ((struct ns_common *)(inode)->i_private)
extern void *ns_get_path(struct path *path, struct task_struct *task,
const struct proc_ns_operations *ns_ops);
extern int ns_get_name(char *buf, size_t size, struct task_struct *task,
const struct proc_ns_operations *ns_ops);
extern void nsfs_init(void);
#endif /* _LINUX_PROC_NS_H */