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

4 files changed, 55 insertions, 5 deletions

diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
index c2d09bc4f976..80c4181e194a 100644
--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -63,17 +63,20 @@
 
 #define __free(_name)	__cleanup(__free_##_name)
 
-#define __get_and_null_ptr(p) \
-	({ __auto_type __ptr = &(p); \
-	   __auto_type __val = *__ptr; \
-	   *__ptr = NULL;  __val; })
+#define __get_and_null(p, nullvalue)   \
+	({                                  \
+		__auto_type __ptr = &(p);   \
+		__auto_type __val = *__ptr; \
+		*__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)
 
diff --git a/include/linux/file.h b/include/linux/file.h
index 45d0f4800abd..237931f20739 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -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);
diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
index 5601d14e2886..dab6a1734a22 100644
--- a/include/linux/nsproxy.h
+++ b/include/linux/nsproxy.h
@@ -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
diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h
index 72ec000a97cd..565fc0629fff 100644
--- a/include/uapi/linux/pidfd.h
+++ b/include/uapi/linux/pidfd.h
@@ -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 */