SystemSan: arbitrary DNS resolution detection (google#8448)

cc @oliverchang @jonathanmetzman 

Here is a new bug class for SystemSan : arbitrary DNS resolution (like
in log4j)

What do you think about it ?

infra/experimental/SystemSan/Makefile

@@ -2,9 +2,9 @@
 CXX     = clang++
 CFLAGS = -std=c++17 -Wall -Wextra -O3 -g3
 
-all: clean SystemSan target target_file
+all: clean SystemSan target target_file target_dns
 
-SystemSan: SystemSan.cpp
+SystemSan: SystemSan.cpp inspect_dns.cpp inspect_utils.cpp
 	$(CXX) $(CFLAGS) -lpthread -o $@ $^
 
 target: target.cpp
@@ -13,9 +13,13 @@ target: target.cpp
 target_file: target_file.cpp
 	$(CXX) $(CFLAGS) -fsanitize=address,fuzzer -o $@ $^
 
+target_dns: target_dns.cpp
+	$(CXX) $(CFLAGS) -fsanitize=address,fuzzer -o $@ $^
+
 test:  all vuln.dict
 	./SystemSan ./target -dict=vuln.dict
 	./SystemSan ./target_file -dict=vuln.dict
+	./SystemSan ./target_dns -dict=vuln.dict
 
 pytorch-lightning-1.5.10:
 	cp SystemSan.cpp PoEs/pytorch-lightning-1.5.10/; \
@@ -30,4 +34,4 @@ node-shell-quote-v1.7.3:
 	docker run -t systemsan_node-shell-quote:latest;
 
 clean:
-	rm -f SystemSan /tmp/tripwire target target_file
+	rm -f SystemSan /tmp/tripwire target target_file target_dns

infra/experimental/SystemSan/SystemSan.cpp

@@ -40,6 +40,9 @@
 #include <string>
 #include <vector>
 
+#include "inspect_utils.h"
+#include "inspect_dns.h"
+
 #define DEBUG_LOGS 0
 
 #if DEBUG_LOGS
@@ -162,23 +165,6 @@ pid_t run_child(char **argv) {
   return pid;
 }
 
-std::vector<std::byte> read_memory(pid_t pid, unsigned long long address,
-                                   size_t size) {
-  std::vector<std::byte> memory;
-
-  for (size_t i = 0; i < size; i += sizeof(long)) {
-    long word = ptrace(PTRACE_PEEKTEXT, pid, address + i, 0);
-    if (word == -1) {
-      return memory;
-    }
-
-    std::byte *word_bytes = reinterpret_cast<std::byte *>(&word);
-    memory.insert(memory.end(), word_bytes, word_bytes + sizeof(long));
-  }
-
-  return memory;
-}
-
 // Construct a string with the memory specified in a register.
 std::string read_string(pid_t pid, unsigned long reg, unsigned long length) {
   auto memory = read_memory(pid, reg, length);
@@ -191,27 +177,6 @@ std::string read_string(pid_t pid, unsigned long reg, unsigned long length) {
   return content;
 }
 
-void report_bug(std::string bug_type, pid_t tid) {
-  // Report the bug found based on the bug code.
-  std::cerr << "===BUG DETECTED: " << bug_type.c_str() << "===\n";
-  // Rely on sanitizers/libFuzzer to produce a stacktrace by sending SIGABRT
-  // to the root process.
-  // Note: this may not be reliable or consistent if shell injection happens
-  // in an async way.
-  // Find the thread group id, that is the pid.
-  pid_t pid = tid;
-  auto parent = root_pids[tid];
-  while (!parent.ran_exec) {
-    // Find the first parent which ran exec syscall.
-    if (parent.parent_tid == g_root_pid) {
-      break;
-    }
-    pid = parent.parent_tid;
-    parent = root_pids[parent.parent_tid];
-  }
-  tgkill(pid, tid, SIGABRT);
-}
-
 void inspect_for_injection(pid_t pid, const user_regs_struct &regs) {
   // Inspect a PID's registers for the sign of shell injection.
   std::string path = read_string(pid, regs.rdi, kTripWire.length());
@@ -459,6 +424,8 @@ int trace(std::map<pid_t, Tracee> pids) {
             }
           }
 
+          inspect_dns_syscalls(pid, regs);
+
           if (regs.orig_rax == __NR_openat) {
             inspect_for_arbitrary_file_open(pid, regs);
           }

infra/experimental/SystemSan/inspect_dns.cpp

@@ -0,0 +1,235 @@
+/*
+ * 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. */
+
+/* POSIX */
+#include <sys/user.h>
+#include <unistd.h>
+
+/* Linux */
+#include <sys/ptrace.h>
+#include <syscall.h>
+#include <arpa/inet.h>
+
+#include <iostream>
+
+#include "inspect_utils.h"
+
+// Arbitrary domain name resolution
+const std::string kArbitraryDomainNameResolution = "Arbitrary domain name resolution";
+
+// Global constant for one file descriptor about of a DNS socket
+int kFdDns = 0;
+
+#define DNS_HEADER_LEN 12
+
+
+void inspect_for_arbitrary_dns_connect(pid_t pid, const user_regs_struct &regs) {
+  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;
+    }
+  }
+}
+
+struct DnsHeader {
+  uint16_t tx_id;
+  uint16_t flags;
+  uint16_t questions;
+  uint16_t answers;
+  uint16_t nameservers;
+  uint16_t additional;
+};
+
+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;
+}
+
+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;
+}
+
+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;
+};
+
+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;
+}
+
+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";
+}
+
+void inspect_for_arbitrary_dns_pkt(std::vector<std::byte> data) {
+  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;
+  }
+
+  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);
+    log_dns_request(req, data);
+  }
+}
+
+void inspect_for_arbitrary_dns_fdbuffer(pid_t pid, const user_regs_struct &regs) {
+  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);
+    }
+  }
+}
+
+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);
+    }
+  }
+}
+
+void inspect_for_arbitrary_dns_sendmsg(pid_t pid, const user_regs_struct &regs) {
+  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);
+      }
+    }
+  }
+}
+
+void inspect_for_arbitrary_dns_sendmmsg(pid_t pid, const user_regs_struct &regs) {
+  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);
+      }
+    }
+  }
+}
+
+void inspect_dns_syscalls(pid_t pid, const user_regs_struct &regs) {
+  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);
+  }
+}

infra/experimental/SystemSan/inspect_dns.h

@@ -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. */
+
+
+/* POSIX */
+#include <unistd.h>
+
+/* Linux */
+#include <sys/ptrace.h>
+
+
+void inspect_dns_syscalls(pid_t pid, const user_regs_struct &regs);