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vfs-6.11.pidfs

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Merge tag 'vfs-6.11.pidfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull pidfs updates from Christian Brauner:
 "This contains work to make it possible to derive namespace file
  descriptors from pidfd file descriptors.

  Right now it is already possible to use a pidfd with setns() to
  atomically change multiple namespaces at the same time. In other
  words, it is possible to switch to the namespace context of a process
  using a pidfd. There is no need to first open namespace file
  descriptors via procfs.

  The work included here is an extension of these abilities by allowing
  to open namespace file descriptors using a pidfd. This means it is now
  possible to interact with namespaces without ever touching procfs.

  To this end a new set of ioctls() on pidfds is introduced covering all
  supported namespace types"

* tag 'vfs-6.11.pidfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  pidfs: allow retrieval of namespace file descriptors
  nsfs: add open_namespace()
  nsproxy: add helper to go from arbitrary namespace to ns_common
  nsproxy: add a cleanup helper for nsproxy
  file: add take_fd() cleanup helper
This commit is contained in:
Linus Torvalds 2024-07-15 12:34:01 -07:00
commit 98f3a9a4fd
7 changed files with 179 additions and 30 deletions
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2
fs/internal.h
View file

@ -17,6 +17,7 @@ struct fs_context;
struct pipe_inode_info;
struct iov_iter;
struct mnt_idmap;
struct ns_common;
/*
* block/bdev.c
@ -239,6 +240,7 @@ extern void mnt_pin_kill(struct mount *m);
* fs/nsfs.c
*/
extern const struct dentry_operations ns_dentry_operations;
int open_namespace(struct ns_common *ns);
/*
* fs/stat.c:

57
fs/nsfs.c
View file

@ -84,40 +84,47 @@ int ns_get_path(struct path *path, struct task_struct *task,
return ns_get_path_cb(path, ns_get_path_task, &args);
}
int open_related_ns(struct ns_common *ns,
struct ns_common *(*get_ns)(struct ns_common *ns))
/**
* open_namespace - open a namespace
* @ns: the namespace to open
*
* This will consume a reference to @ns indendent of success or failure.
*
* Return: A file descriptor on success or a negative error code on failure.
*/
int open_namespace(struct ns_common *ns)
{
struct path path = {};
struct ns_common *relative;
struct path path __free(path_put) = {};
struct file *f;
int err;
int fd;
fd = get_unused_fd_flags(O_CLOEXEC);
/* call first to consume reference */
err = path_from_stashed(&ns->stashed, nsfs_mnt, ns, &path);
if (err < 0)
return err;
CLASS(get_unused_fd, fd)(O_CLOEXEC);
if (fd < 0)
return fd;
relative = get_ns(ns);
if (IS_ERR(relative)) {
put_unused_fd(fd);
return PTR_ERR(relative);
}
err = path_from_stashed(&relative->stashed, nsfs_mnt, relative, &path);
if (err < 0) {
put_unused_fd(fd);
return 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);
if (IS_ERR(f))
return PTR_ERR(f);
return fd;
fd_install(fd, f);
return take_fd(fd);
}
int open_related_ns(struct ns_common *ns,
struct ns_common *(*get_ns)(struct ns_common *ns))
{
struct ns_common *relative;
relative = get_ns(ns);
if (IS_ERR(relative))
return PTR_ERR(relative);
return open_namespace(relative);
}
EXPORT_SYMBOL_GPL(open_related_ns);

90
fs/pidfs.c
View file

@ -11,10 +11,16 @@
#include <linux/proc_fs.h>
#include <linux/proc_ns.h>
#include <linux/pseudo_fs.h>
#include <linux/ptrace.h>
#include <linux/seq_file.h>
#include <uapi/linux/pidfd.h>
#include <linux/ipc_namespace.h>
#include <linux/time_namespace.h>
#include <linux/utsname.h>
#include <net/net_namespace.h>
#include "internal.h"
#include "mount.h"
#ifdef CONFIG_PROC_FS
/**
@ -108,11 +114,95 @@ static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
return poll_flags;
}
static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct task_struct *task __free(put_task) = NULL;
struct nsproxy *nsp __free(put_nsproxy) = NULL;
struct pid *pid = pidfd_pid(file);
struct ns_common *ns_common;
if (arg)
return -EINVAL;
task = get_pid_task(pid, PIDTYPE_PID);
if (!task)
return -ESRCH;
scoped_guard(task_lock, task) {
nsp = task->nsproxy;
if (nsp)
get_nsproxy(nsp);
}
if (!nsp)
return -ESRCH; /* just pretend it didn't exist */
/*
* We're trying to open a file descriptor to the namespace so perform a
* filesystem cred ptrace check. Also, we mirror nsfs behavior.
*/
if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
return -EACCES;
switch (cmd) {
/* Namespaces that hang of nsproxy. */
case PIDFD_GET_CGROUP_NAMESPACE:
get_cgroup_ns(nsp->cgroup_ns);
ns_common = to_ns_common(nsp->cgroup_ns);
break;
case PIDFD_GET_IPC_NAMESPACE:
get_ipc_ns(nsp->ipc_ns);
ns_common = to_ns_common(nsp->ipc_ns);
break;
case PIDFD_GET_MNT_NAMESPACE:
get_mnt_ns(nsp->mnt_ns);
ns_common = to_ns_common(nsp->mnt_ns);
break;
case PIDFD_GET_NET_NAMESPACE:
ns_common = to_ns_common(nsp->net_ns);
get_net_ns(ns_common);
break;
case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE:
get_pid_ns(nsp->pid_ns_for_children);
ns_common = to_ns_common(nsp->pid_ns_for_children);
break;
case PIDFD_GET_TIME_NAMESPACE:
get_time_ns(nsp->time_ns);
ns_common = to_ns_common(nsp->time_ns);
break;
case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE:
get_time_ns(nsp->time_ns_for_children);
ns_common = to_ns_common(nsp->time_ns_for_children);
break;
case PIDFD_GET_UTS_NAMESPACE:
get_uts_ns(nsp->uts_ns);
ns_common = to_ns_common(nsp->uts_ns);
break;
/* Namespaces that don't hang of nsproxy. */
case PIDFD_GET_USER_NAMESPACE:
rcu_read_lock();
ns_common = to_ns_common(get_user_ns(task_cred_xxx(task, user_ns)));
rcu_read_unlock();
break;
case PIDFD_GET_PID_NAMESPACE:
rcu_read_lock();
ns_common = to_ns_common(get_pid_ns(task_active_pid_ns(task)));
rcu_read_unlock();
break;
default:
return -ENOIOCTLCMD;
}
/* open_namespace() unconditionally consumes the reference */
return open_namespace(ns_common);
}
static const struct file_operations pidfs_file_operations = {
.poll = pidfd_poll,
#ifdef CONFIG_PROC_FS
.show_fdinfo = pidfd_show_fdinfo,
#endif
.unlocked_ioctl = pidfd_ioctl,
.compat_ioctl = compat_ptr_ioctl,
};
struct pid *pidfd_pid(const struct file *file)

11
include/linux/cleanup.h
View file

@ -63,17 +63,20 @@
#define __free(_name) __cleanup(__free_##_name)
#define __get_and_null_ptr(p) \
({ __auto_type __ptr = &(p); \
#define __get_and_null(p, nullvalue) \
({ \
__auto_type __ptr = &(p); \
__auto_type __val = *__ptr; \
*__ptr = NULL; __val; })
*__ptr = nullvalue; \
__val; \
})
static inline __must_check
const volatile void * __must_check_fn(const volatile void *val)
{ return val; }
#define no_free_ptr(p) \
((typeof(p)) __must_check_fn(__get_and_null_ptr(p)))
((typeof(p)) __must_check_fn(__get_and_null(p, NULL)))
#define return_ptr(p) return no_free_ptr(p)

20
include/linux/file.h
View file

@ -97,6 +97,26 @@ extern void put_unused_fd(unsigned int fd);
DEFINE_CLASS(get_unused_fd, int, if (_T >= 0) put_unused_fd(_T),
get_unused_fd_flags(flags), unsigned flags)
/*
* take_fd() will take care to set @fd to -EBADF ensuring that
* CLASS(get_unused_fd) won't call put_unused_fd(). This makes it
* easier to rely on CLASS(get_unused_fd):
*
* struct file *f;
*
* CLASS(get_unused_fd, fd)(O_CLOEXEC);
* if (fd < 0)
* return fd;
*
* f = dentry_open(&path, O_RDONLY, current_cred());
* if (IS_ERR(f))
* return PTR_ERR(fd);
*
* fd_install(fd, f);
* return take_fd(fd);
*/
#define take_fd(fd) __get_and_null(fd, -EBADF)
extern void fd_install(unsigned int fd, struct file *file);
int receive_fd(struct file *file, int __user *ufd, unsigned int o_flags);

13
include/linux/nsproxy.h
View file

@ -42,6 +42,17 @@ struct nsproxy {
};
extern struct nsproxy init_nsproxy;
#define to_ns_common(__ns) \
_Generic((__ns), \
struct cgroup_namespace *: &(__ns->ns), \
struct ipc_namespace *: &(__ns->ns), \
struct net *: &(__ns->ns), \
struct pid_namespace *: &(__ns->ns), \
struct mnt_namespace *: &(__ns->ns), \
struct time_namespace *: &(__ns->ns), \
struct user_namespace *: &(__ns->ns), \
struct uts_namespace *: &(__ns->ns))
/*
* A structure to encompass all bits needed to install
* a partial or complete new set of namespaces.
@ -112,4 +123,6 @@ static inline void get_nsproxy(struct nsproxy *ns)
refcount_inc(&ns->count);
}
DEFINE_FREE(put_nsproxy, struct nsproxy *, if (_T) put_nsproxy(_T))
#endif

14
include/uapi/linux/pidfd.h
View file

@ -5,6 +5,7 @@
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/ioctl.h>
/* Flags for pidfd_open(). */
#define PIDFD_NONBLOCK O_NONBLOCK
@ -15,4 +16,17 @@
#define PIDFD_SIGNAL_THREAD_GROUP (1UL << 1)
#define PIDFD_SIGNAL_PROCESS_GROUP (1UL << 2)
#define PIDFS_IOCTL_MAGIC 0xFF
#define PIDFD_GET_CGROUP_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 1)
#define PIDFD_GET_IPC_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 2)
#define PIDFD_GET_MNT_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 3)
#define PIDFD_GET_NET_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 4)
#define PIDFD_GET_PID_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 5)
#define PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 6)
#define PIDFD_GET_TIME_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 7)
#define PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 8)
#define PIDFD_GET_USER_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 9)
#define PIDFD_GET_UTS_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 10)
#endif /* _UAPI_LINUX_PIDFD_H */