From 5b08bd408534bfb3a7cf5778da5b27d4e4fffe12 Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Thu, 27 Jun 2024 16:11:42 +0200
Subject: [PATCH] pidfs: allow retrieval of namespace file descriptors
For users that hold a reference to a pidfd procfs might not even be
available nor is it desirable to parse through procfs just for the sake
of getting namespace file descriptors for a process.
Make it possible to directly retrieve namespace file descriptors from a
pidfd. Pidfds already can be used with setns() to change a set of
namespaces atomically.
Link: https://lore.kernel.org/r/20240627-work-pidfs-v1-4-7e9ab6cc3bb1@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
fs/pidfs.c | 90 ++++++++++++++++++++++++++++++++++++++
include/uapi/linux/pidfd.h | 14 ++++++
2 files changed, 104 insertions(+)
diff --git a/fs/pidfs.c b/fs/pidfs.c
index dbb9d854d1c57..c9cb14181deff 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -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)
diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h
index 72ec000a97cda..565fc0629fff5 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 */
--
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