ublk: fix ublksrv pid handling for pid namespaces

When ublksrv runs inside a pid namespace, START/END_RECOVERY compared
the stored init-ns tgid against the userspace pid (getpid vnr), so the
check failed and control ops could not proceed. Compare against the
caller’s init-ns tgid and store that value, then translate it back to
the caller’s pid namespace when reporting GET_DEV_INFO so ublk list
shows a sensible pid.

Testing: start/recover in a pid namespace; `ublk list` shows
reasonable pid values in init, child, and sibling namespaces.

Fixes: d37a224fc119 ("ublk: validate ublk server pid")
Signed-off-by: Seamus Connor <sconnor@purestorage.com>
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>

Author: Seamus Connor

drivers/block/ublk_drv.c

@@ -2946,6 +2946,10 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub,
 	if (wait_for_completion_interruptible(&ub->completion) != 0)
 		return -EINTR;
 
+	rcu_read_lock();
+	ublksrv_pid = pid_nr(find_vpid(ublksrv_pid));
+	rcu_read_unlock();
+
 	if (ub->ublksrv_tgid != ublksrv_pid)
 		return -EINVAL;
 
@@ -3313,12 +3317,32 @@ static int ublk_ctrl_stop_dev(struct ublk_device *ub)
 static int ublk_ctrl_get_dev_info(struct ublk_device *ub,
 		const struct ublksrv_ctrl_cmd *header)
 {
+	struct task_struct *p;
+	struct pid *pid;
+	struct ublksrv_ctrl_dev_info dev_info;
+	pid_t init_ublksrv_tgid = ub->dev_info.ublksrv_pid;
 	void __user *argp = (void __user *)(unsigned long)header->addr;
 
 	if (header->len < sizeof(struct ublksrv_ctrl_dev_info) || !header->addr)
 		return -EINVAL;
 
-	if (copy_to_user(argp, &ub->dev_info, sizeof(ub->dev_info)))
+	memcpy(&dev_info, &ub->dev_info, sizeof(dev_info));
+	dev_info.ublksrv_pid = -1;
+
+	if (init_ublksrv_tgid > 0) {
+		rcu_read_lock();
+		pid = find_pid_ns(init_ublksrv_tgid, &init_pid_ns);
+		p = pid_task(pid, PIDTYPE_TGID);
+		if (p) {
+			int vnr = task_tgid_vnr(p);
+
+			if (vnr)
+				dev_info.ublksrv_pid = vnr;
+		}
+		rcu_read_unlock();
+	}
+
+	if (copy_to_user(argp, &dev_info, sizeof(dev_info)))
 		return -EFAULT;
 
 	return 0;
@@ -3463,6 +3487,10 @@ static int ublk_ctrl_end_recovery(struct ublk_device *ub,
 	pr_devel("%s: All FETCH_REQs received, dev id %d\n", __func__,
 		 header->dev_id);
 
+	rcu_read_lock();
+	ublksrv_pid = pid_nr(find_vpid(ublksrv_pid));
+	rcu_read_unlock();
+
 	if (ub->ublksrv_tgid != ublksrv_pid)
 		return -EINVAL;