From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Frediano Ziglio Date: Fri, 18 May 2018 11:41:57 +0100 Subject: [PATCH] Fix flexible array buffer overflow This is kind of a DoS, possibly flexible array in the protocol causes the network size check to be ignored due to integer overflows. The size of flexible array is computed as (message_end - position), then this size is added to the number of bytes before the array and this number is used to check if we overflow initial message. An example is: message { uint32 dummy[2]; uint8 data[] @end; } LenMessage; which generated this (simplified remove useless code) code: { /* data */ data__nelements = message_end - (start + 8); data__nw_size = data__nelements; } nw_size = 8 + data__nw_size; /* Check if message fits in reported side */ if (nw_size > (uintptr_t) (message_end - start)) { return NULL; } Following code: - data__nelements == message_end - (start + 8) - data__nw_size == data__nelements == message_end - (start + 8) - nw_size == 8 + data__nw_size == 8 + message_end - (start + 8) == 8 + message_end - start - 8 == message_end -start - the check for overflow is (nw_size > (message_end - start)) but nw_size == message_end - start so the check is doing ((message_end - start) > (message_end - start)) which is always false. If message_end - start < 8 then data__nelements (number of element on the array above) computation generate an integer underflow that later create a buffer overflow. Add a check to make sure that the array starts before the message ends to avoid the overflow. Difference is: diff -u save/generated_client_demarshallers1.c common/generated_client_demarshallers1.c - - save/generated_client_demarshallers1.c 2018-06-22 22:13:48.626793919 +0100 + + common/generated_client_demarshallers1.c 2018-06-22 22:14:03.408163291 +0100 @@ -225,6 +225,9 @@ uint64_t data__nelements; { /* data */ + if (SPICE_UNLIKELY((start + 0) > message_end)) { + goto error; + } data__nelements = message_end - (start + 0); data__nw_size = data__nelements; @@ -243,6 +246,9 @@ *free_message = nofree; return data; + error: + free(data); + return NULL; } static uint8_t * parse_msg_set_ack(uint8_t *message_start, uint8_t *message_end, SPICE_GNUC_UNUSED int minor, size_t *size, message_destructor_t *free_message) @@ -301,6 +307,9 @@ SpiceMsgPing *out; { /* data */ + if (SPICE_UNLIKELY((start + 12) > message_end)) { + goto error; + } data__nelements = message_end - (start + 12); data__nw_size = data__nelements; @@ -5226,6 +5235,9 @@ uint64_t cursor_data__nw_size; uint64_t cursor_data__nelements; { /* data */ + if (SPICE_UNLIKELY((start2 + 22) > message_end)) { + goto error; + } cursor_data__nelements = message_end - (start2 + 22); cursor_data__nw_size = cursor_data__nelements; @@ -5305,6 +5317,9 @@ uint64_t cursor_data__nw_size; uint64_t cursor_data__nelements; { /* data */ + if (SPICE_UNLIKELY((start2 + 22) > message_end)) { + goto error; + } cursor_data__nelements = message_end - (start2 + 22); cursor_data__nw_size = cursor_data__nelements; @@ -5540,6 +5555,9 @@ SpiceMsgPlaybackPacket *out; { /* data */ + if (SPICE_UNLIKELY((start + 4) > message_end)) { + goto error; + } data__nelements = message_end - (start + 4); data__nw_size = data__nelements; @@ -5594,6 +5612,9 @@ SpiceMsgPlaybackMode *out; { /* data */ + if (SPICE_UNLIKELY((start + 8) > message_end)) { + goto error; + } data__nelements = message_end - (start + 8); data__nw_size = data__nelements; diff -u save/generated_client_demarshallers.c common/generated_client_demarshallers.c - - save/generated_client_demarshallers.c 2018-06-22 22:13:48.626793919 +0100 + + common/generated_client_demarshallers.c 2018-06-22 22:14:03.004153195 +0100 @@ -225,6 +225,9 @@ uint64_t data__nelements; { /* data */ + if (SPICE_UNLIKELY((start + 0) > message_end)) { + goto error; + } data__nelements = message_end - (start + 0); data__nw_size = data__nelements; @@ -243,6 +246,9 @@ *free_message = nofree; return data; + error: + free(data); + return NULL; } static uint8_t * parse_msg_set_ack(uint8_t *message_start, uint8_t *message_end, SPICE_GNUC_UNUSED int minor, size_t *size, message_destructor_t *free_message) @@ -301,6 +307,9 @@ SpiceMsgPing *out; { /* data */ + if (SPICE_UNLIKELY((start + 12) > message_end)) { + goto error; + } data__nelements = message_end - (start + 12); data__nw_size = data__nelements; @@ -6574,6 +6583,9 @@ } { /* data */ + if (SPICE_UNLIKELY((start2 + 2 + cursor_u__nw_size) > message_end)) { + goto error; + } cursor_data__nelements = message_end - (start2 + 2 + cursor_u__nw_size); cursor_data__nw_size = cursor_data__nelements; @@ -6670,6 +6682,9 @@ } { /* data */ + if (SPICE_UNLIKELY((start2 + 2 + cursor_u__nw_size) > message_end)) { + goto error; + } cursor_data__nelements = message_end - (start2 + 2 + cursor_u__nw_size); cursor_data__nw_size = cursor_data__nelements; @@ -6907,6 +6922,9 @@ SpiceMsgPlaybackPacket *out; { /* data */ + if (SPICE_UNLIKELY((start + 4) > message_end)) { + goto error; + } data__nelements = message_end - (start + 4); data__nw_size = data__nelements; @@ -6961,6 +6979,9 @@ SpiceMsgPlaybackMode *out; { /* data */ + if (SPICE_UNLIKELY((start + 6) > message_end)) { + goto error; + } data__nelements = message_end - (start + 6); data__nw_size = data__nelements; @@ -7559,6 +7580,9 @@ SpiceMsgTunnelSocketData *out; { /* data */ + if (SPICE_UNLIKELY((start + 2) > message_end)) { + goto error; + } data__nelements = message_end - (start + 2); data__nw_size = data__nelements; @@ -7840,6 +7864,9 @@ } { /* compressed_data */ + if (SPICE_UNLIKELY((start + 1 + u__nw_size) > message_end)) { + goto error; + } compressed_data__nelements = message_end - (start + 1 + u__nw_size); compressed_data__nw_size = compressed_data__nelements; diff -u save/generated_server_demarshallers.c common/generated_server_demarshallers.c - - save/generated_server_demarshallers.c 2018-06-22 22:13:48.627793944 +0100 + + common/generated_server_demarshallers.c 2018-06-22 22:14:05.231208847 +0100 @@ -306,6 +306,9 @@ uint64_t data__nelements; { /* data */ + if (SPICE_UNLIKELY((start + 0) > message_end)) { + goto error; + } data__nelements = message_end - (start + 0); data__nw_size = data__nelements; @@ -324,6 +327,9 @@ *free_message = nofree; return data; + error: + free(data); + return NULL; } static uint8_t * parse_msgc_disconnecting(uint8_t *message_start, uint8_t *message_end, SPICE_GNUC_UNUSED int minor, size_t *size, message_destructor_t *free_message) @@ -1259,6 +1265,9 @@ SpiceMsgcRecordPacket *out; { /* data */ + if (SPICE_UNLIKELY((start + 4) > message_end)) { + goto error; + } data__nelements = message_end - (start + 4); data__nw_size = data__nelements; @@ -1313,6 +1322,9 @@ SpiceMsgcRecordMode *out; { /* data */ + if (SPICE_UNLIKELY((start + 6) > message_end)) { + goto error; + } data__nelements = message_end - (start + 6); data__nw_size = data__nelements; @@ -1841,6 +1853,9 @@ SpiceMsgcTunnelSocketData *out; { /* data */ + if (SPICE_UNLIKELY((start + 2) > message_end)) { + goto error; + } data__nelements = message_end - (start + 2); data__nw_size = data__nelements; @@ -2057,6 +2072,9 @@ } { /* compressed_data */ + if (SPICE_UNLIKELY((start + 1 + u__nw_size) > message_end)) { + goto error; + } compressed_data__nelements = message_end - (start + 1 + u__nw_size); compressed_data__nw_size = compressed_data__nelements; Signed-off-by: Frediano Ziglio --- spice-common/python_modules/demarshal.py | 1 + 1 file changed, 1 insertion(+) diff --git a/spice-common/python_modules/demarshal.py b/spice-common/python_modules/demarshal.py index 1ea131d..7172762 100644 --- a/spice-common/python_modules/demarshal.py +++ b/spice-common/python_modules/demarshal.py @@ -318,6 +318,7 @@ def write_validate_array_item(writer, container, item, scope, parent_scope, star writer.assign(nelements, array.size) elif array.is_remaining_length(): if element_type.is_fixed_nw_size(): + writer.error_check("%s > message_end" % item.get_position()) if element_type.get_fixed_nw_size() == 1: writer.assign(nelements, "message_end - %s" % item.get_position()) else: