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SystemSan: arbitrary DNS resolution detection
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| Original file line number | Diff line number | Diff line change |
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| /* | ||
| * Copyright 2022 Google LLC | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
| /* A detector that uses ptrace to identify shell injection vulnerabilities. */ | ||
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| /* POSIX */ | ||
| #include <sys/user.h> | ||
| #include <unistd.h> | ||
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| /* Linux */ | ||
| #include <sys/ptrace.h> | ||
| #include <syscall.h> | ||
| #include <arpa/inet.h> | ||
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| #include <iostream> | ||
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| #include "inspect_utils.h" | ||
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| // Arbitrary domain name resolution | ||
| const std::string kArbitraryDomainNameResolution = "Arbitrary domain name resolution"; | ||
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| // Global constant for one file descriptor about of a DNS socket | ||
| int kFdDns = 0; | ||
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| #define DNS_HEADER_LEN 12 | ||
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| void inspect_for_arbitrary_dns_connect(pid_t pid, const user_regs_struct ®s) { | ||
| auto memory = read_memory(pid, regs.rsi, sizeof(struct sockaddr_in)); | ||
| if (memory.size()) { | ||
| struct sockaddr_in * sa = reinterpret_cast<struct sockaddr_in *>(memory.data()); | ||
| if (sa->sin_family == AF_INET && htons(sa->sin_port) == 53) { | ||
| // save file descriptor for later sendmmsg | ||
| kFdDns = regs.rdi; | ||
| } | ||
| } | ||
| } | ||
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| struct DnsHeader { | ||
| uint16_t tx_id; | ||
| uint16_t flags; | ||
| uint16_t questions; | ||
| uint16_t answers; | ||
| uint16_t nameservers; | ||
| uint16_t additional; | ||
| }; | ||
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| struct DnsHeader parse_dns_header(std::vector<std::byte> data) { | ||
| struct DnsHeader h; | ||
| h.tx_id = (((uint16_t) data[0]) << 8) | ((uint16_t) data[1]); | ||
| h.flags = (((uint16_t) data[2]) << 8) | ((uint16_t) data[3]); | ||
| h.questions = (((uint16_t) data[4]) << 8) | ((uint16_t) data[5]); | ||
| h.answers = (((uint16_t) data[6]) << 8) | ((uint16_t) data[7]); | ||
| h.nameservers = (((uint16_t) data[8]) << 8) | ((uint16_t) data[9]); | ||
| h.additional = (((uint16_t) data[10]) << 8) | ((uint16_t) data[11]); | ||
| return h; | ||
| } | ||
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| bool dns_flags_standard_query(uint16_t flags) { | ||
| if ((flags & 0x8000) == 0) { | ||
| // Query, not response. | ||
| if (((flags & 0x7800) >> 11) == 0) { | ||
| // Opcode 0 is standard query. | ||
| if ((flags & 0x0200) == 0) { | ||
| // Message is not truncated. | ||
| if ((flags & 0x0040) == 0) { | ||
| // Z-bit reserved flag is unset. | ||
| return true; | ||
| } | ||
| } | ||
| } | ||
| } | ||
| return false; | ||
| } | ||
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| struct DnsRequest { | ||
| // Start of name in the byte vector. | ||
| size_t offset; | ||
| // End of name in the byte vector. | ||
| size_t end; | ||
| // Length of top level domain. | ||
| uint8_t tld_size; | ||
| // Number of levels/dots in domain name. | ||
| size_t nb_levels; | ||
| // DNS type like A is 1. | ||
| uint16_t dns_type; | ||
| // DNS class like IN is 1. | ||
| uint16_t dns_class; | ||
| }; | ||
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| struct DnsRequest parse_dns_request(std::vector<std::byte> data, size_t offset) { | ||
| struct DnsRequest r; | ||
| r.offset = offset; | ||
| r.tld_size = 0; | ||
| r.nb_levels = 0; | ||
| while(offset < data.size()) { | ||
| uint8_t rlen = uint8_t(data[offset]); | ||
| if (rlen == 0) { | ||
| break; | ||
| } | ||
| r.nb_levels++; | ||
| offset += rlen+1; | ||
| r.tld_size = rlen; | ||
| } | ||
| if (offset <= 4 + data.size()) { | ||
| r.end = offset; | ||
| r.dns_type = (((uint16_t) data[offset]) << 8) | ((uint16_t) data[offset+1]); | ||
| r.dns_class = (((uint16_t) data[offset+2]) << 8) | ((uint16_t) data[offset+3]); | ||
| } else { | ||
| r.end = data.size(); | ||
| } | ||
| return r; | ||
| } | ||
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| void log_dns_request(struct DnsRequest r, std::vector<std::byte> data) { | ||
| size_t offset = r.offset; | ||
| std::cerr << "===Domain resolved: "; | ||
| while(offset < r.end) { | ||
| uint8_t rlen = uint8_t(data[offset]); | ||
| if (rlen == 0) { | ||
| break; | ||
| } | ||
| std::cerr << '.'; | ||
| for (uint8_t i = 1; i < rlen+1; i++) { | ||
| std::cerr << (char) data[offset + i]; | ||
| } | ||
| offset += rlen+1; | ||
| } | ||
| std::cerr << "===\n"; | ||
| std::cerr << "===DNS request type: " << r.dns_type << ", class: " << r.dns_class << "===\n"; | ||
| } | ||
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| void inspect_for_arbitrary_dns_pkt(std::vector<std::byte> data, pid_t pid) { | ||
| if (data.size() < DNS_HEADER_LEN + 1) { | ||
| return; | ||
| } | ||
| struct DnsHeader h = parse_dns_header(data); | ||
| if (h.questions != 1) { | ||
| return; | ||
| } | ||
| if (h.answers != 0 || h.nameservers != 0 || h.additional != 0) { | ||
| return; | ||
| } | ||
| if (!dns_flags_standard_query(h.flags)) { | ||
| return; | ||
| } | ||
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| struct DnsRequest req = parse_dns_request(data, DNS_HEADER_LEN); | ||
| // Alert if the top level domain is only one character and | ||
| // if there is more than just the TLD. | ||
| if (req.tld_size == 1 && req.nb_levels > 1 && req.end < data.size()) { | ||
| report_bug(kArbitraryDomainNameResolution, pid); | ||
| log_dns_request(req, data); | ||
| } | ||
| } | ||
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| void inspect_for_arbitrary_dns_fdbuffer(pid_t pid, const user_regs_struct ®s) { | ||
| if (kFdDns > 0 && kFdDns == (int) regs.rdi) { | ||
| auto memory = read_memory(pid, regs.rsi, regs.rdx); | ||
| if (memory.size()) { | ||
| inspect_for_arbitrary_dns_pkt(memory, pid); | ||
| } | ||
| } | ||
| } | ||
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| void inspect_for_arbitrary_dns_iov(pid_t pid, unsigned long iov) { | ||
| auto memory = read_memory(pid, iov, sizeof(struct iovec)); | ||
| if (memory.size()) { | ||
| struct iovec * iovec = reinterpret_cast<struct iovec *>(memory.data()); | ||
| memory = read_memory(pid, (unsigned long) iovec->iov_base, iovec->iov_len); | ||
| if (memory.size()) { | ||
| inspect_for_arbitrary_dns_pkt(memory, pid); | ||
| } | ||
| } | ||
| } | ||
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| void inspect_for_arbitrary_dns_sendmsg(pid_t pid, const user_regs_struct ®s) { | ||
| if (kFdDns > 0 && kFdDns == (int) regs.rdi) { | ||
| auto memory = read_memory(pid, regs.rsi, sizeof(struct msghdr)); | ||
| if (memory.size()) { | ||
| struct msghdr * msg = reinterpret_cast<struct msghdr *>(memory.data()); | ||
| if (msg->msg_iovlen == 1) { | ||
| inspect_for_arbitrary_dns_iov(pid, (unsigned long) msg->msg_iov); | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| void inspect_for_arbitrary_dns_sendmmsg(pid_t pid, const user_regs_struct ®s) { | ||
| if (kFdDns > 0 && kFdDns == (int) regs.rdi) { | ||
| auto memory = read_memory(pid, regs.rsi, sizeof(struct mmsghdr)); | ||
| if (memory.size()) { | ||
| struct mmsghdr * msg = reinterpret_cast<struct mmsghdr *>(memory.data()); | ||
| if (msg->msg_hdr.msg_iovlen == 1) { | ||
| inspect_for_arbitrary_dns_iov(pid, (unsigned long) msg->msg_hdr.msg_iov); | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| void inspect_dns_syscalls(pid_t pid, const user_regs_struct ®s) { | ||
| switch (regs.orig_rax) { | ||
| case __NR_connect: | ||
| inspect_for_arbitrary_dns_connect(pid, regs); | ||
| break; | ||
| case __NR_close: | ||
| if (kFdDns > 0 && kFdDns == (int) regs.rdi) { | ||
| // reset DNS file descriptor on close | ||
| kFdDns = 0; | ||
| } | ||
| break; | ||
| case __NR_sendmmsg: | ||
| inspect_for_arbitrary_dns_sendmmsg(pid, regs); | ||
| break; | ||
| case __NR_sendmsg: | ||
| inspect_for_arbitrary_dns_sendmsg(pid, regs); | ||
| break; | ||
| case __NR_sendto: | ||
| // fallthrough | ||
| case __NR_write: | ||
| inspect_for_arbitrary_dns_fdbuffer(pid, regs); | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,26 @@ | ||
| /* | ||
| * Copyright 2022 Google LLC | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
| /* A detector that uses ptrace to identify DNS arbitrary resolutions. */ | ||
|
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|
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| /* POSIX */ | ||
| #include <unistd.h> | ||
|
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| /* Linux */ | ||
| #include <sys/ptrace.h> | ||
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| void inspect_dns_syscalls(pid_t pid, const user_regs_struct ®s); |
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