1011-Always-allocate-domid-sequentially-and-do-not-reuse-.patch

From 5f8607649d9601eb421a4ee137bce5a4449076d3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Marczykowski-G=C3=B3recki?=
 <marmarek@invisiblethingslab.com>
Date: Fri, 3 Dec 2021 21:13:23 +0100
Subject: [PATCH] Always allocate domid sequentially, and do not reuse them

While domid wrapping around is unlikely on Qubes, make sure it wont
happen, to avoid various corner cases.
---
 xen/common/domctl.c | 36 +++++++++++++-----------------------
 1 file changed, 13 insertions(+), 23 deletions(-)

diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 2c0331bb05ed..459a3a502154 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -412,32 +412,22 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
     case XEN_DOMCTL_createdomain:
     {
         domid_t        dom;
-        static domid_t rover = 0;
+        static domid_t rover = 1;
 
-        dom = op->domain;
-        if ( (dom > 0) && (dom < DOMID_FIRST_RESERVED) )
-        {
-            ret = -EEXIST;
-            if ( !is_free_domid(dom) )
-                break;
-        }
-        else
-        {
-            for ( dom = rover + 1; dom != rover; dom++ )
-            {
-                if ( dom == DOMID_FIRST_RESERVED )
-                    dom = 1;
-                if ( is_free_domid(dom) )
-                    break;
-            }
-
-            ret = -ENOMEM;
-            if ( dom == rover )
-                break;
-
-            rover = dom;
+        /* Refuse explicit domid via op->domain */
+        if ( (op->domain > 0) && (op->domain < DOMID_FIRST_RESERVED) )
+            return -EINVAL;
+
+        if ( rover >= DOMID_FIRST_RESERVED ) {
+            printk(XENLOG_ERR
+                   "domctl: out of available domid values, reboot the system\n");
+            return -ENOMEM;
         }
 
+        dom = rover++;
+        if ( ! is_free_domid(dom) )
+            return -EEXIST;
+
         d = domain_create(dom, &op->u.createdomain, false);
         if ( IS_ERR(d) )
         {
-- 
2.44.0