LXC: Fix virLXCControllerSetupDevPTS() wrt user namespaces

The gid value passed to devpts has to be translated by hand as
virLXCControllerSetupDevPTS() is called before setting up the user
and group mappings.
Otherwise devpts will use an unmapped gid and openpty()
will fail within containers.
Linux kernel commit 23adbe12
("fs,userns: Change inode_capable to capable_wrt_inode_uidgid")
uncovered that issue.
Signed-off-by: NRichard Weinberger <richard@nod.at>
Signed-off-by: NJán Tomko <jtomko@redhat.com>

src/lxc/lxc_controller.c

@@ -1164,6 +1164,20 @@ static int virLXCControllerMain(virLXCControllerPtr ctrl)
     return rc;
 }
 
+static unsigned int
+virLXCControllerLookupUsernsMap(virDomainIdMapEntryPtr map,
+                                int num,
+                                unsigned int src)
+{
+    size_t i;
+
+    for (i = 0; i < num; i++) {
+        if (src > map[i].start && src < map[i].start + map[i].count)
+            return map[i].target + (src - map[i].start);
+    }
+
+    return src;
+}
 
 static int
 virLXCControllerSetupUsernsMap(virDomainIdMapEntryPtr map,
@@ -1930,6 +1944,7 @@ virLXCControllerSetupDevPTS(virLXCControllerPtr ctrl)
     char *opts = NULL;
     char *devpts = NULL;
     int ret = -1;
+    gid_t ptsgid = 5;
 
     VIR_DEBUG("Setting up private /dev/pts");
 
@@ -1949,10 +1964,15 @@ virLXCControllerSetupDevPTS(virLXCControllerPtr ctrl)
         goto cleanup;
     }
 
+    if (ctrl->def->idmap.ngidmap)
+        ptsgid = virLXCControllerLookupUsernsMap(ctrl->def->idmap.gidmap,
+                                                 ctrl->def->idmap.ngidmap,
+                                                 ptsgid);
+
     /* XXX should we support gid=X for X!=5 for distros which use
      * a different gid for tty?  */
-    if (virAsprintf(&opts, "newinstance,ptmxmode=0666,mode=0620,gid=5%s",
-                    (mount_options ? mount_options : "")) < 0)
+    if (virAsprintf(&opts, "newinstance,ptmxmode=0666,mode=0620,gid=%u%s",
+                    ptsgid, (mount_options ? mount_options : "")) < 0)
         goto cleanup;
 
     VIR_DEBUG("Mount devpts on %s type=tmpfs flags=%x, opts=%s",