From 5901cb001d929249c5c0848ec1eadd8918b2c12f Mon Sep 17 00:00:00 2001
From: "Enrico Weigelt, metux IT consult" <info@metux.net>
Date: Thu, 25 Jan 2024 16:38:10 +0100
Subject: [PATCH] Xnamespace: add selection isolation

Selection names (as seen by the client) are internally prefixed with the
namespace ID, so each client can only access those within it's namespace.

If a client within namespace "foo" want's to operate on "PRIMARY",
it actually will be doing so on "<foo>PRIMARY", w/o ever noticing it.
Events will sent back to the client still pointing to "PRIMARY".

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
---
 Xext/namespace/hook-selection.c | 67 +++++++++++++++++++++++++++++++++
 Xext/namespace/hooks.h          |  1 +
 Xext/namespace/meson.build      |  1 +
 Xext/namespace/namespace.c      |  4 +-
 4 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 Xext/namespace/hook-selection.c

diff --git a/Xext/namespace/hook-selection.c b/Xext/namespace/hook-selection.c
new file mode 100644
index 000000000..f0edf27ad
--- /dev/null
+++ b/Xext/namespace/hook-selection.c
@@ -0,0 +1,67 @@
+#define HOOK_NAME "selection"
+
+#include <dix-config.h>
+
+#include <stdio.h>
+
+#include "dix/selection_priv.h"
+
+#include "namespace.h"
+#include "hooks.h"
+
+static inline const char *stripNS(const char* name) {
+    if ((!name) || (name[0] != '<'))
+        return name; // can this ever happen ?
+    const char *got = strchr(name, '>');
+    if (!got)
+        return name;
+    return ++got;
+}
+
+/*
+ * This hook is rewriting the client visible selection names to internally used,
+ * per namespace ones. Whenever a client is asking for a selection, it's name
+ * is replaced by a namespaced one, e.g. asking for "PRIMARY" while being in
+ * namespace "foo" will become "<foo>PRIMARY"
+ *
+ * A malicious client could still send specially crafted messages to others,
+ * asking them to send their selection data to him. This needs to be solved
+ * separately, by a send hook.
+ */
+void hookSelectionFilter(CallbackListPtr *pcbl, void *unused, void *calldata)
+{
+    XNS_HOOK_HEAD(SelectionFilterParamRec);
+
+    /* no rewrite if client is in root namespace */
+    if (subj->ns->superPower)
+        return;
+
+    const char *origSelectionName = NameForAtom(param->selection);
+
+    char selname[PATH_MAX] = { 0 };
+    snprintf(selname, sizeof(selname)-1, "<%s>%s", subj->ns->name, origSelectionName);
+    Atom realSelection = MakeAtom(selname, strlen(selname), TRUE);
+
+    switch (param->op) {
+        case SELECTION_FILTER_GETOWNER:
+        case SELECTION_FILTER_SETOWNER:
+        case SELECTION_FILTER_CONVERT:
+        case SELECTION_FILTER_LISTEN:
+            // TODO: check whether window really belongs to the client
+            param->selection = realSelection;
+        break;
+
+        case SELECTION_FILTER_NOTIFY:
+        {
+            // need to translate back, since we're having the ns-prefixed name here
+            const char *stripped = stripNS(origSelectionName);
+            param->selection = MakeAtom(stripped, strlen(stripped), TRUE);
+            break;
+        }
+
+        // nothing to do here: already having the client visible name
+        case SELECTION_FILTER_EV_REQUEST:
+        case SELECTION_FILTER_EV_CLEAR:
+        break;
+    }
+}
diff --git a/Xext/namespace/hooks.h b/Xext/namespace/hooks.h
index 3043ec93f..d06408c52 100644
--- a/Xext/namespace/hooks.h
+++ b/Xext/namespace/hooks.h
@@ -25,5 +25,6 @@
     struct XnamespaceClientPriv *subj = XnsClientPriv(client);
 
 void hookClientState(CallbackListPtr *pcbl, void *unused, void *calldata);
+void hookSelectionFilter(CallbackListPtr *pcbl, void *unused, void *calldata);
 
 #endif /* __XSERVER_NAMESPACE_HOOKS_H */
diff --git a/Xext/namespace/meson.build b/Xext/namespace/meson.build
index d6a693bb8..165882231 100644
--- a/Xext/namespace/meson.build
+++ b/Xext/namespace/meson.build
@@ -3,6 +3,7 @@ libxserver_namespace = static_library(
 	[
 		'config.c',
 		'hook-clientstate.c',
+		'hook-selection.c',
 		'namespace.c',
 	],
 	include_directories: inc,
diff --git a/Xext/namespace/namespace.c b/Xext/namespace/namespace.c
index 845c2e585..b2aa59913 100644
--- a/Xext/namespace/namespace.c
+++ b/Xext/namespace/namespace.c
@@ -4,6 +4,7 @@
 #include <X11/Xmd.h>
 
 #include "dix/dix_priv.h"
+#include "dix/selection_priv.h"
 #include "include/os.h"
 #include "miext/extinit_priv.h"
 
@@ -27,7 +28,8 @@ NamespaceExtensionInit(void)
 
     if (!(dixRegisterPrivateKey(&namespaceClientPrivKeyRec, PRIVATE_CLIENT,
             sizeof(struct XnamespaceClientPriv)) &&
-          AddCallback(&ClientStateCallback, hookClientState, NULL)))
+          AddCallback(&ClientStateCallback, hookClientState, NULL) &&
+          AddCallback(&SelectionFilterCallback, hookSelectionFilter, NULL)))
         FatalError("NamespaceExtensionInit: allocation failure\n");
 
     /* Do the serverClient */