From d1a24f7e4313dc72ee4863a47a8dd71454192f97 Mon Sep 17 00:00:00 2001 From: Marc Mutz Date: Mon, 3 Oct 2016 22:19:45 +0200 Subject: [PATCH] DBusMessage: Fix UB (misaligned access) in call to _dbus_header_set_field_basic() The const void* 'value' pointer that is passed the address of a uint32_t here eventually ends up in _dbus_marshal_write_basic(), which casts it to a DBusBasicValue, a union type that has an alignment of eight on 64-bit platforms and is therefore more-aligned than the uint32. The read of a value of a more-aligned type through a pointer to a less -aligned type is undefined behaviour. Fix by storing the uint32 in a DBusBasicValue and passing that instead. Found by UBSan: dbus/dbus/dbus-marshal-basic.c:832:14: runtime error: member access within misaligned address 0x7fdb8dac3a04 for type 'const union DBusBasicValue', which requires 8 byte alignment 0x7fdb8dac3a04: note: pointer points here 4a 87 b5 71 01 00 00 00 40 7d 01 00 00 61 00 00 10 3b ac 8d db 7f 00 00 2c 2a 3e 94 db 7f 00 00 ^ #0 0x7fdb9444a2c3 in _dbus_marshal_write_basic dbus/dbus/dbus-marshal-basic.c:832 #1 0x7fdb943d22fb in _dbus_type_writer_write_basic_no_typecode dbus/dbus/dbus-marshal-recursive.c:1605 #2 0x7fdb943d64e9 in _dbus_type_writer_write_basic dbus/dbus/dbus-marshal-recursive.c:2327 #3 0x7fdb943c52a6 in write_basic_field dbus/dbus/dbus-marshal-header.c:318 #4 0x7fdb943c919e in _dbus_header_set_field_basic dbus/dbus/dbus-marshal-header.c:1321 #5 0x7fdb943e1349 in dbus_message_set_reply_serial dbus/dbus/dbus-message.c:1173 Signed-off-by: Marc Mutz --- dbus/dbus-message.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/dbus/dbus-message.c b/dbus/dbus-message.c index 547f248..3255bd7 100644 --- a/dbus/dbus-message.c +++ b/dbus/dbus-message.c @@ -1170,10 +1170,11 @@ dbus_message_set_reply_serial (DBusMessage *message, _dbus_return_val_if_fail (!message->locked, FALSE); _dbus_return_val_if_fail (reply_serial != 0, FALSE); /* 0 is invalid */ + const DBusBasicValue value = reply_serial; return _dbus_header_set_field_basic (&message->header, DBUS_HEADER_FIELD_REPLY_SERIAL, DBUS_TYPE_UINT32, - &reply_serial); + &value); } /** -- 2.7.4