From e5a3a3df1d594fd2fdfafdf25d14c0e3794483c7 Mon Sep 17 00:00:00 2001 From: David Cermak Date: Wed, 2 Feb 2022 12:21:12 +0100 Subject: [PATCH] mdns: Fix potential read behind parsed packet * Original commit: espressif/esp-idf@51a5de2525d0e82adea2e298a0edcc9b2dee5edd --- components/mdns/mdns.c | 77 ++++++++++++-------- examples/protocols/mdns/mdns_example_test.py | 1 + 2 files changed, 48 insertions(+), 30 deletions(-) diff --git a/components/mdns/mdns.c b/components/mdns/mdns.c index cd9f997c1..5c4fa377a 100644 --- a/components/mdns/mdns.c +++ b/components/mdns/mdns.c @@ -332,10 +332,11 @@ static mdns_srv_item_t *_mdns_get_service_item_instance(const char *instance, co * * @return the address after the parsed FQDN in the packet or NULL on error */ -static const uint8_t * _mdns_read_fqdn(const uint8_t * packet, const uint8_t * start, mdns_name_t * name, char * buf) +static const uint8_t * _mdns_read_fqdn(const uint8_t * packet, const uint8_t * start, mdns_name_t * name, char * buf, size_t packet_len) { size_t index = 0; - while (start[index]) { + const uint8_t * packet_end = packet + packet_len; + while (start + index < packet_end && start[index]) { if (name->parts == 4) { name->invalid = true; } @@ -347,6 +348,9 @@ static const uint8_t * _mdns_read_fqdn(const uint8_t * packet, const uint8_t * s } uint8_t i; for (i=0; i= packet_end) { + return NULL; + } buf[i] = start[index++]; } buf[len] = '\0'; @@ -369,7 +373,7 @@ static const uint8_t * _mdns_read_fqdn(const uint8_t * packet, const uint8_t * s //reference address can not be after where we are return NULL; } - if (_mdns_read_fqdn(packet, packet + address, name, buf)) { + if (_mdns_read_fqdn(packet, packet + address, name, buf, packet_len)) { return start + index; } return NULL; @@ -569,7 +573,7 @@ static inline int append_one_txt_record_entry(uint8_t * packet, uint16_t * index * * @return length of added data: 0 on error or length on success */ -static uint16_t _mdns_append_fqdn(uint8_t * packet, uint16_t * index, const char * strings[], uint8_t count) +static uint16_t _mdns_append_fqdn(uint8_t * packet, uint16_t * index, const char * strings[], uint8_t count, size_t packet_len) { if (!count) { //empty string so terminate @@ -596,7 +600,7 @@ search_next: name.service[0] = 0; name.proto[0] = 0; name.domain[0] = 0; - const uint8_t * content = _mdns_read_fqdn(packet, len_location, &name, buf); + const uint8_t * content = _mdns_read_fqdn(packet, len_location, &name, buf, packet_len); if (!content) { //not a readable fqdn? return 0; @@ -622,7 +626,7 @@ search_next: return 0; } //run the same for the other strings in the name - return written + _mdns_append_fqdn(packet, index, &strings[1], count - 1); + return written + _mdns_append_fqdn(packet, index, &strings[1], count - 1, packet_len); } //we have found the string so let's insert a pointer to it instead @@ -656,7 +660,7 @@ static uint16_t _mdns_append_ptr_record(uint8_t * packet, uint16_t * index, cons str[2] = proto; str[3] = MDNS_DEFAULT_DOMAIN; - part_length = _mdns_append_fqdn(packet, index, str + 1, 3); + part_length = _mdns_append_fqdn(packet, index, str + 1, 3, MDNS_MAX_PACKET_SIZE); if (!part_length) { return 0; } @@ -669,7 +673,7 @@ static uint16_t _mdns_append_ptr_record(uint8_t * packet, uint16_t * index, cons record_length += part_length; uint16_t data_len_location = *index - 2; - part_length = _mdns_append_fqdn(packet, index, str, 4); + part_length = _mdns_append_fqdn(packet, index, str, 4, MDNS_MAX_PACKET_SIZE); if (!part_length) { return 0; } @@ -704,7 +708,7 @@ static uint16_t _mdns_append_subtype_ptr_record(uint8_t *packet, uint16_t *index return 0; } - part_length = _mdns_append_fqdn(packet, index, subtype_str, ARRAY_SIZE(subtype_str)); + part_length = _mdns_append_fqdn(packet, index, subtype_str, ARRAY_SIZE(subtype_str), MDNS_MAX_PACKET_SIZE); if (!part_length) { return 0; } @@ -717,7 +721,7 @@ static uint16_t _mdns_append_subtype_ptr_record(uint8_t *packet, uint16_t *index record_length += part_length; uint16_t data_len_location = *index - 2; - part_length = _mdns_append_fqdn(packet, index, instance_str, ARRAY_SIZE(instance_str)); + part_length = _mdns_append_fqdn(packet, index, instance_str, ARRAY_SIZE(instance_str), MDNS_MAX_PACKET_SIZE); if (!part_length) { return 0; } @@ -756,7 +760,7 @@ static uint16_t _mdns_append_sdptr_record(uint8_t * packet, uint16_t * index, md str[1] = service->proto; str[2] = MDNS_DEFAULT_DOMAIN; - part_length = _mdns_append_fqdn(packet, index, sd_str, 4); + part_length = _mdns_append_fqdn(packet, index, sd_str, 4, MDNS_MAX_PACKET_SIZE); record_length += part_length; @@ -767,7 +771,7 @@ static uint16_t _mdns_append_sdptr_record(uint8_t * packet, uint16_t * index, md record_length += part_length; uint16_t data_len_location = *index - 2; - part_length = _mdns_append_fqdn(packet, index, str, 3); + part_length = _mdns_append_fqdn(packet, index, str, 3, MDNS_MAX_PACKET_SIZE); if (!part_length) { return 0; } @@ -805,7 +809,7 @@ static uint16_t _mdns_append_txt_record(uint8_t * packet, uint16_t * index, mdns return 0; } - part_length = _mdns_append_fqdn(packet, index, str, 4); + part_length = _mdns_append_fqdn(packet, index, str, 4, MDNS_MAX_PACKET_SIZE); if (!part_length) { return 0; } @@ -869,7 +873,7 @@ static uint16_t _mdns_append_srv_record(uint8_t * packet, uint16_t * index, mdns return 0; } - part_length = _mdns_append_fqdn(packet, index, str, 4); + part_length = _mdns_append_fqdn(packet, index, str, 4, MDNS_MAX_PACKET_SIZE); if (!part_length) { return 0; } @@ -902,7 +906,7 @@ static uint16_t _mdns_append_srv_record(uint8_t * packet, uint16_t * index, mdns return 0; } - part_length = _mdns_append_fqdn(packet, index, str, 2); + part_length = _mdns_append_fqdn(packet, index, str, 2, MDNS_MAX_PACKET_SIZE); if (!part_length) { return 0; } @@ -935,7 +939,7 @@ static uint16_t _mdns_append_a_record(uint8_t * packet, uint16_t * index, const return 0; } - part_length = _mdns_append_fqdn(packet, index, str, 2); + part_length = _mdns_append_fqdn(packet, index, str, 2, MDNS_MAX_PACKET_SIZE); if (!part_length) { return 0; } @@ -987,7 +991,7 @@ static uint16_t _mdns_append_aaaa_record(uint8_t * packet, uint16_t * index, con } - part_length = _mdns_append_fqdn(packet, index, str, 2); + part_length = _mdns_append_fqdn(packet, index, str, 2, MDNS_MAX_PACKET_SIZE); if (!part_length) { return 0; } @@ -1035,7 +1039,7 @@ static uint16_t _mdns_append_question(uint8_t * packet, uint16_t * index, mdns_o str[str_index++] = q->domain; } - part_length = _mdns_append_fqdn(packet, index, str, str_index); + part_length = _mdns_append_fqdn(packet, index, str, str_index, MDNS_MAX_PACKET_SIZE); if (!part_length) { return 0; } @@ -2958,7 +2962,7 @@ static inline uint32_t _mdns_read_u32(const uint8_t * packet, uint16_t index) * * @return the address after the parsed FQDN in the packet or NULL on error */ -static const uint8_t * _mdns_parse_fqdn(const uint8_t * packet, const uint8_t * start, mdns_name_t * name) +static const uint8_t * _mdns_parse_fqdn(const uint8_t * packet, const uint8_t * start, mdns_name_t * name, size_t packet_len) { name->parts = 0; name->sub = 0; @@ -2970,7 +2974,7 @@ static const uint8_t * _mdns_parse_fqdn(const uint8_t * packet, const uint8_t * static char buf[MDNS_NAME_BUF_LEN]; - const uint8_t * next_data = (uint8_t*)_mdns_read_fqdn(packet, start, name, buf); + const uint8_t * next_data = (uint8_t*)_mdns_read_fqdn(packet, start, name, buf, packet_len); if (!next_data) { return 0; } @@ -3243,6 +3247,10 @@ void mdns_parse_packet(mdns_rx_packet_t * packet) mdns_name_t * name = &n; memset(name, 0, sizeof(mdns_name_t)); + if (len <= MDNS_HEAD_ADDITIONAL_OFFSET) { + free(parsed_packet); + return; + } header.id = _mdns_read_u16(data, MDNS_HEAD_ID_OFFSET); header.flags.value = _mdns_read_u16(data, MDNS_HEAD_FLAGS_OFFSET); header.questions = _mdns_read_u16(data, MDNS_HEAD_QUESTIONS_OFFSET); @@ -3274,7 +3282,7 @@ void mdns_parse_packet(mdns_rx_packet_t * packet) uint8_t qs = header.questions; while (qs--) { - content = _mdns_parse_fqdn(data, content, name); + content = _mdns_parse_fqdn(data, content, name, len); if (!content) { header.answers = 0; header.additional = 0; @@ -3282,6 +3290,9 @@ void mdns_parse_packet(mdns_rx_packet_t * packet) goto clear_rx_packet;//error } + if (content + MDNS_CLASS_OFFSET + 1 >= data + len) { + goto clear_rx_packet; // malformed packet, won't read behind it + } uint16_t type = _mdns_read_u16(content, MDNS_TYPE_OFFSET); uint16_t mdns_class = _mdns_read_u16(content, MDNS_CLASS_OFFSET); bool unicast = !!(mdns_class & 0x8000); @@ -3353,11 +3364,14 @@ void mdns_parse_packet(mdns_rx_packet_t * packet) while (content < (data + len)) { - content = _mdns_parse_fqdn(data, content, name); + content = _mdns_parse_fqdn(data, content, name, len); if (!content) { goto clear_rx_packet;//error } + if (content + MDNS_LEN_OFFSET + 1 >= data + len) { + goto clear_rx_packet; // malformed packet, won't read behind it + } uint16_t type = _mdns_read_u16(content, MDNS_TYPE_OFFSET); uint16_t mdns_class = _mdns_read_u16(content, MDNS_CLASS_OFFSET); uint32_t ttl = _mdns_read_u32(content, MDNS_TTL_OFFSET); @@ -3403,7 +3417,7 @@ void mdns_parse_packet(mdns_rx_packet_t * packet) } if (type == MDNS_TYPE_PTR) { - if (!_mdns_parse_fqdn(data, data_ptr, name)) { + if (!_mdns_parse_fqdn(data, data_ptr, name, len)) { continue;//error } if (search_result) { @@ -3442,9 +3456,12 @@ void mdns_parse_packet(mdns_rx_packet_t * packet) } } - if (!_mdns_parse_fqdn(data, data_ptr + MDNS_SRV_FQDN_OFFSET, name)) { + if (!_mdns_parse_fqdn(data, data_ptr + MDNS_SRV_FQDN_OFFSET, name, len)) { continue;//error } + if (data_ptr + MDNS_SRV_PORT_OFFSET + 1 >= data + len) { + goto clear_rx_packet; // malformed packet, won't read behind it + } uint16_t priority = _mdns_read_u16(data_ptr, MDNS_SRV_PRIORITY_OFFSET); uint16_t weight = _mdns_read_u16(data_ptr, MDNS_SRV_WEIGHT_OFFSET); uint16_t port = _mdns_read_u16(data_ptr, MDNS_SRV_PORT_OFFSET); @@ -5852,8 +5869,8 @@ void mdns_debug_packet(const uint8_t * data, size_t len) uint8_t qs = header.questions; while (qs--) { - content = _mdns_parse_fqdn(data, content, name); - if (!content) { + content = _mdns_parse_fqdn(data, content, name, len); + if (!content || content + MDNS_CLASS_OFFSET + 1 >= data + len) { header.answers = 0; header.additional = 0; header.servers = 0; @@ -5903,7 +5920,7 @@ void mdns_debug_packet(const uint8_t * data, size_t len) while (content < (data + len)) { - content = _mdns_parse_fqdn(data, content, name); + content = _mdns_parse_fqdn(data, content, name, len); if (!content) { _mdns_dbg_printf("ERROR: parse mdns records\n"); break; @@ -5971,13 +5988,13 @@ void mdns_debug_packet(const uint8_t * data, size_t len) _mdns_dbg_printf("%u ", ttl); _mdns_dbg_printf("[%u] ", data_len); if (type == MDNS_TYPE_PTR) { - if (!_mdns_parse_fqdn(data, data_ptr, name)) { + if (!_mdns_parse_fqdn(data, data_ptr, name, len)) { _mdns_dbg_printf("ERROR: parse PTR\n"); continue; } _mdns_dbg_printf("%s.%s.%s.%s.\n", name->host, name->service, name->proto, name->domain); } else if (type == MDNS_TYPE_SRV) { - if (!_mdns_parse_fqdn(data, data_ptr + MDNS_SRV_FQDN_OFFSET, name)) { + if (!_mdns_parse_fqdn(data, data_ptr + MDNS_SRV_FQDN_OFFSET, name, len)) { _mdns_dbg_printf("ERROR: parse SRV\n"); continue; } @@ -6015,7 +6032,7 @@ void mdns_debug_packet(const uint8_t * data, size_t len) _mdns_dbg_printf(IPSTR "\n", IP2STR(&ip)); } else if (type == MDNS_TYPE_NSEC) { const uint8_t * old_ptr = data_ptr; - const uint8_t * new_ptr = _mdns_parse_fqdn(data, data_ptr, name); + const uint8_t * new_ptr = _mdns_parse_fqdn(data, data_ptr, name, len); if (new_ptr) { _mdns_dbg_printf("%s.%s.%s.%s. ", name->host, name->service, name->proto, name->domain); size_t diff = new_ptr - old_ptr; diff --git a/examples/protocols/mdns/mdns_example_test.py b/examples/protocols/mdns/mdns_example_test.py index 20e6bad04..fbd062a43 100644 --- a/examples/protocols/mdns/mdns_example_test.py +++ b/examples/protocols/mdns/mdns_example_test.py @@ -91,6 +91,7 @@ def mdns_server(esp_host): console_log('Received query: {} '.format(dns.__repr__())) sock.sendto(get_dns_answer_to_mdns_lwip(TESTER_NAME_LWIP, dns.id), addr) if len(dns.an) > 0 and dns.an[0].type == dpkt.dns.DNS_A: + console_log('Received answer from {}'.format(dns.an[0].name)) if dns.an[0].name == esp_host + u'.local': console_log('Received answer to esp32-mdns query: {}'.format(dns.__repr__())) esp_answered.set()