From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Jan Kara <jack@suse.cz>,
	Christian Brauner <brauner@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.12 0991/1102] nscommon: simplify initialization
Date: Thu, 17 Sep 2026 16:15:34 +0100
Message-ID: <20260917151605.594963317@linuxfoundation.org>
In-Reply-To: <20260917151539.408551884@linuxfoundation.org>
References: <20260917151539.408551884@linuxfoundation.org>
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6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christian Brauner <brauner@kernel.org>

[ Upstream commit 5612ff3ec588be09f11a9424db6d1186bcdeb3fa ]

There's a lot of information that namespace implementers don't need to
know about at all. Encapsulate this all in the initialization helper.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

[ sashal: Reduced backport -- upstream 5612ff3ec588b touches 10 file(s), this
  backport carries 1. Not backported here:
  fs/namespace.c
  include/linux/ns_common.h
  ipc/namespace.c
  kernel/cgroup/namespace.c
  kernel/nscommon.c
  kernel/pid_namespace.c
  kernel/time/namespace.c
  kernel/user_namespace.c
  ... and 2 more
  This note is generated from the file lists only; see the resolution record
  for the reasoning. ]

Stable-dep-of: 9688a4680293 ("pidfd: hold exec_update_lock around namespace ioctl")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/pidfs.c |   22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -115,21 +115,27 @@ static __poll_t pidfd_poll(struct file *
 	return poll_flags;
 }
 
+#define pidfs_ioctl_valid(cmd) \
+	(_IOC_TYPE(cmd) == PIDFS_IOCTL_MAGIC && _IOC_DIR(cmd) == _IOC_NONE && \
+	 _IOC_NR(cmd) >= _IOC_NR(PIDFD_GET_CGROUP_NAMESPACE) && \
+	 _IOC_NR(cmd) <= _IOC_NR(PIDFD_GET_UTS_NAMESPACE))
+
 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 = NULL;
-	struct pid_namespace *pid_ns;
 
-	if (arg)
-		return -EINVAL;
+	if (!pidfs_ioctl_valid(cmd))
+		return -ENOIOCTLCMD;
 
-	task = get_pid_task(pid, PIDTYPE_PID);
+	task = get_pid_task(pidfd_pid(file), PIDTYPE_PID);
 	if (!task)
 		return -ESRCH;
 
+	if (arg)
+		return -EINVAL;
+
 	scoped_guard(task_lock, task) {
 		nsp = task->nsproxy;
 		if (nsp)
@@ -202,13 +208,17 @@ static long pidfd_ioctl(struct file *fil
 		}
 		break;
 	case PIDFD_GET_PID_NAMESPACE:
-		if (IS_ENABLED(CONFIG_PID_NS)) {
+#ifdef CONFIG_PID_NS
+		{
+			struct pid_namespace *pid_ns;
+
 			rcu_read_lock();
 			pid_ns = task_active_pid_ns(task);
 			if (pid_ns)
 				ns_common = to_ns_common(get_pid_ns(pid_ns));
 			rcu_read_unlock();
 		}
+#endif
 		break;
 	default:
 		return -ENOIOCTLCMD;