From 8f382ee405ec68850866298ba0574f12e261a6fa Mon Sep 17 00:00:00 2001

From: Simon McVittie <smcv@collabora.com>

Date: Tue, 13 Sep 2022 15:10:22 +0100

Subject: [PATCH] dbus-marshal-validate: Check brackets in signature nest

 correctly

In debug builds with assertions enabled, a signature with incorrectly

nested `()` and `{}`, for example `a{i(u}` or `(a{ii)}`, could result

in an assertion failure.

In production builds without assertions enabled, a signature with

incorrectly nested `()` and `{}` could potentially result in a crash

or incorrect message parsing, although we do not have a concrete example

of either of these failure modes.

Thanks: Evgeny Vereshchagin

Resolves: https://gitlab.freedesktop.org/dbus/dbus/-/issues/418

Resolves: CVE-2022-42010

Signed-off-by: Simon McVittie <smcv@collabora.com>

(cherry picked from commit 9d07424e9011e3bbe535e83043d335f3093d2916)

(cherry picked from commit 3e53a785dee8d1432156188a2c4260e4cbc78c4d)

---

 dbus/dbus-marshal-validate.c | 38 +++++++++++++++++++++++++++++++++++-

 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/dbus/dbus-marshal-validate.c b/dbus/dbus-marshal-validate.c

index 4d492f3f3..ae68414dd 100644

--- a/dbus/dbus-marshal-validate.c

+++ b/dbus/dbus-marshal-validate.c

@@ -62,6 +62,8 @@ _dbus_validate_signature_with_reason (const DBusString *type_str,

   int element_count;

   DBusList *element_count_stack;

+  char opened_brackets[DBUS_MAXIMUM_TYPE_RECURSION_DEPTH * 2 + 1] = { '\0' };

+  char last_bracket;

   result = DBUS_VALID;

   element_count_stack = NULL;

@@ -93,6 +95,10 @@ _dbus_validate_signature_with_reason (const DBusString *type_str,

   while (p != end)

     {

+      _dbus_assert (struct_depth + dict_entry_depth >= 0);

+      _dbus_assert (struct_depth + dict_entry_depth < _DBUS_N_ELEMENTS (opened_brackets));

+      _dbus_assert (opened_brackets[struct_depth + dict_entry_depth] == '\0');

+

       switch (*p)

         {

         case DBUS_TYPE_BYTE:

@@ -136,6 +142,10 @@ _dbus_validate_signature_with_reason (const DBusString *type_str,

               goto out;

             }

+          _dbus_assert (struct_depth + dict_entry_depth >= 1);

+          _dbus_assert (struct_depth + dict_entry_depth < _DBUS_N_ELEMENTS (opened_brackets));

+          _dbus_assert (opened_brackets[struct_depth + dict_entry_depth - 1] == '\0');

+          opened_brackets[struct_depth + dict_entry_depth - 1] = DBUS_STRUCT_BEGIN_CHAR;

           break;

         case DBUS_STRUCT_END_CHAR:

@@ -151,9 +161,20 @@ _dbus_validate_signature_with_reason (const DBusString *type_str,

               goto out;

             }

+          _dbus_assert (struct_depth + dict_entry_depth >= 1);

+          _dbus_assert (struct_depth + dict_entry_depth < _DBUS_N_ELEMENTS (opened_brackets));

+          last_bracket = opened_brackets[struct_depth + dict_entry_depth - 1];

+

+          if (last_bracket != DBUS_STRUCT_BEGIN_CHAR)

+            {

+              result = DBUS_INVALID_STRUCT_ENDED_BUT_NOT_STARTED;

+              goto out;

+            }

+

           _dbus_list_pop_last (&element_count_stack);

           struct_depth -= 1;

+          opened_brackets[struct_depth + dict_entry_depth] = '\0';

           break;

         case DBUS_DICT_ENTRY_BEGIN_CHAR:

@@ -178,6 +199,10 @@ _dbus_validate_signature_with_reason (const DBusString *type_str,

               goto out;

             }

+          _dbus_assert (struct_depth + dict_entry_depth >= 1);

+          _dbus_assert (struct_depth + dict_entry_depth < _DBUS_N_ELEMENTS (opened_brackets));

+          _dbus_assert (opened_brackets[struct_depth + dict_entry_depth - 1] == '\0');

+          opened_brackets[struct_depth + dict_entry_depth - 1] = DBUS_DICT_ENTRY_BEGIN_CHAR;

           break;

         case DBUS_DICT_ENTRY_END_CHAR:

@@ -186,8 +211,19 @@ _dbus_validate_signature_with_reason (const DBusString *type_str,

               result = DBUS_INVALID_DICT_ENTRY_ENDED_BUT_NOT_STARTED;

               goto out;

             }

-            

+

+          _dbus_assert (struct_depth + dict_entry_depth >= 1);

+          _dbus_assert (struct_depth + dict_entry_depth < _DBUS_N_ELEMENTS (opened_brackets));

+          last_bracket = opened_brackets[struct_depth + dict_entry_depth - 1];

+

+          if (last_bracket != DBUS_DICT_ENTRY_BEGIN_CHAR)

+            {

+              result = DBUS_INVALID_DICT_ENTRY_ENDED_BUT_NOT_STARTED;

+              goto out;

+            }

+

           dict_entry_depth -= 1;

+          opened_brackets[struct_depth + dict_entry_depth] = '\0';

           element_count = 

             _DBUS_POINTER_TO_INT (_dbus_list_pop_last (&element_count_stack));

-- 

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