Add syscall sandboxing (seccomp-bpf)

Author: practicalswift

ci/test/00_setup_env_i686_multiprocess.sh

@@ -14,4 +14,5 @@ export DEP_OPTS="DEBUG=1 MULTIPROCESS=1"
 export GOAL="install"
 export BITCOIN_CONFIG="--enable-debug CC='clang -m32' CXX='clang++ -m32' LDFLAGS='--rtlib=compiler-rt -lgcc_s'"
 export TEST_RUNNER_ENV="BITCOIND=bitcoin-node"
+export TEST_RUNNER_EXTRA="--nosandbox"
 export PIP_PACKAGES="lief"

configure.ac

@@ -71,6 +71,12 @@ case $host in
   ;;
 esac
 
+AC_ARG_WITH([seccomp],
+  [AS_HELP_STRING([--with-seccomp],
+  [enable experimental syscall sandbox feature (-sandbox), default is yes if seccomp-bpf is detected under Linux x86_64])],
+  [seccomp_found=$withval],
+  [seccomp_found=auto])
+
 dnl Require C++17 compiler (no GNU extensions)
 AX_CXX_COMPILE_STDCXX([17], [noext], [mandatory])
 
@@ -1443,6 +1449,36 @@ if test "x$use_external_signer" != xno; then
 fi
 AM_CONDITIONAL([ENABLE_EXTERNAL_SIGNER], [test "x$use_external_signer" = "xyes"])
 
+dnl Do not compile with syscall sandbox support when compiling under the sanitizers.
+dnl The sanitizers introduce use of syscalls that are not typically used in bitcoind
+dnl (such as execve when the sanitizers execute llvm-symbolizer).
+if test x$use_sanitizers != x; then
+  AC_MSG_WARN(Specifying --with-sanitizers forces --without-seccomp since the sanitizers introduce use of syscalls not allowed by the bitcoind syscall sandbox (-sandbox=<mode>).)
+  seccomp_found=no
+fi
+if test "x$seccomp_found" != "xno"; then
+  AC_MSG_CHECKING([for seccomp-bpf (Linux x86-64)])
+  AC_PREPROC_IFELSE([AC_LANG_PROGRAM([[
+      @%:@include <linux/seccomp.h>
+    ]], [[
+      #if !defined(__x86_64__)
+      #  error Syscall sandbox is an experimental feature currently available only under Linux x86-64.
+      #endif
+    ]])],[
+      AC_MSG_RESULT(yes)
+      seccomp_found="yes"
+      AC_DEFINE(USE_SYSCALL_SANDBOX, 1, [Define this symbol to build with syscall sandbox support.])
+    ],[
+      AC_MSG_RESULT(no)
+      seccomp_found="no"
+  ])
+fi
+dnl Currently only enable -sandbox=<mode> feature if seccomp is found.
+dnl In the future, sandboxing could be also be supported with other
+dnl sandboxing mechanisms besides seccomp.
+use_syscall_sandbox=$seccomp_found
+AM_CONDITIONAL([ENABLE_SYSCALL_SANDBOX], [test "x$use_syscall_sandbox" != "xno"])
+
 dnl Check for reduced exports
 if test x$use_reduce_exports = xyes; then
   AX_CHECK_COMPILE_FLAG([-fvisibility=hidden],[CXXFLAGS="$CXXFLAGS -fvisibility=hidden"],
@@ -1933,6 +1969,7 @@ echo
 echo "Options used to compile and link:"
 echo "  external signer = $use_external_signer"
 echo "  multiprocess    = $build_multiprocess"
+echo "  with experimental syscall sandbox support = $use_syscall_sandbox"
 echo "  with libs       = $build_bitcoin_libs"
 echo "  with wallet     = $enable_wallet"
 if test "x$enable_wallet" != "xno"; then

src/Makefile.am

@@ -261,6 +261,7 @@ BITCOIN_CORE_H = \
   util/sock.h \
   util/spanparsing.h \
   util/string.h \
+  util/syscall_sandbox.h \
   util/system.h \
   util/thread.h \
   util/threadnames.h \
@@ -611,6 +612,7 @@ libbitcoin_util_a_SOURCES = \
   util/spanparsing.cpp \
   util/strencodings.cpp \
   util/string.cpp \
+  util/syscall_sandbox.cpp \
   util/time.cpp \
   util/tokenpipe.cpp \
   $(BITCOIN_CORE_H)

src/bitcoind.cpp

@@ -19,6 +19,7 @@
 #include <shutdown.h>
 #include <util/check.h>
 #include <util/strencodings.h>
+#include <util/syscall_sandbox.h>
 #include <util/system.h>
 #include <util/threadnames.h>
 #include <util/tokenpipe.h>
@@ -238,6 +239,7 @@ static bool AppInit(NodeContext& node, int argc, char* argv[])
         daemon_ep.Close();
     }
 #endif
+    SetSyscallSandboxPolicy(SyscallSandboxPolicy::SHUTOFF);
     if (fRet) {
         WaitForShutdown();
     }

src/checkqueue.h

@@ -7,6 +7,7 @@
 
 #include <sync.h>
 #include <tinyformat.h>
+#include <util/syscall_sandbox.h>
 #include <util/threadnames.h>
 
 #include <algorithm>
@@ -151,6 +152,7 @@ class CCheckQueue
         for (int n = 0; n < threads_num; ++n) {
             m_worker_threads.emplace_back([this, n]() {
                 util::ThreadRename(strprintf("scriptch.%i", n));
+                SetSyscallSandboxPolicy(SyscallSandboxPolicy::VALIDATION_SCRIPT_CHECK);
                 Loop(false /* worker thread */);
             });
         }

src/httpserver.cpp

@@ -12,6 +12,7 @@
 #include <shutdown.h>
 #include <sync.h>
 #include <util/strencodings.h>
+#include <util/syscall_sandbox.h>
 #include <util/system.h>
 #include <util/threadnames.h>
 #include <util/translation.h>
@@ -279,6 +280,7 @@ static void http_reject_request_cb(struct evhttp_request* req, void*)
 static bool ThreadHTTP(struct event_base* base)
 {
     util::ThreadRename("http");
+    SetSyscallSandboxPolicy(SyscallSandboxPolicy::NET_HTTP_SERVER);
     LogPrint(BCLog::HTTP, "Entering http event loop\n");
     event_base_dispatch(base);
     // Event loop will be interrupted by InterruptHTTPServer()
@@ -332,6 +334,7 @@ static bool HTTPBindAddresses(struct evhttp* http)
 static void HTTPWorkQueueRun(WorkQueue<HTTPClosure>* queue, int worker_num)
 {
     util::ThreadRename(strprintf("httpworker.%i", worker_num));
+    SetSyscallSandboxPolicy(SyscallSandboxPolicy::NET_HTTP_SERVER_WORKER);
     queue->Run();
 }
 

src/index/base.cpp

@@ -8,6 +8,7 @@
 #include <node/ui_interface.h>
 #include <shutdown.h>
 #include <tinyformat.h>
+#include <util/syscall_sandbox.h>
 #include <util/thread.h>
 #include <util/translation.h>
 #include <validation.h> // For g_chainman
@@ -123,6 +124,7 @@ static const CBlockIndex* NextSyncBlock(const CBlockIndex* pindex_prev, CChain&
 
 void BaseIndex::ThreadSync()
 {
+    SetSyscallSandboxPolicy(SyscallSandboxPolicy::TX_INDEX);
     const CBlockIndex* pindex = m_best_block_index.load();
     if (!m_synced) {
         auto& consensus_params = Params().GetConsensus();

src/init.cpp

@@ -60,6 +60,7 @@
 #include <util/check.h>
 #include <util/moneystr.h>
 #include <util/string.h>
+#include <util/syscall_sandbox.h>
 #include <util/system.h>
 #include <util/thread.h>
 #include <util/threadnames.h>
@@ -562,6 +563,10 @@ void SetupServerArgs(ArgsManager& argsman)
     hidden_args.emplace_back("-daemonwait");
 #endif
 
+#if defined(USE_SYSCALL_SANDBOX)
+    argsman.AddArg("-sandbox=<mode>", "Use the experimental syscall sandbox in the specified mode (-sandbox=log-and-abort or -sandbox=abort). Allow only expected syscalls to be used by bitcoind. Note that this is an experimental new feature that may cause bitcoind to exit or crash unexpectedly: use with caution. In the \"log-and-abort\" mode the invocation of an unexpected syscall results in a debug handler being invoked which will log the incident and terminate the program (without executing the unexpected syscall). In the \"abort\" mode the invocation of an unexpected syscall results in the entire process being killed immediately by the kernel without executing the unexpected syscall.", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
+#endif // USE_SYSCALL_SANDBOX
+
     // Add the hidden options
     argsman.AddHiddenArgs(hidden_args);
 }
@@ -1018,6 +1023,37 @@ bool AppInitParameterInteraction(const ArgsManager& args)
         return InitError(_("No proxy server specified. Use -proxy=<ip> or -proxy=<ip:port>."));
     }
 
+#if defined(USE_SYSCALL_SANDBOX)
+    if (args.IsArgSet("-sandbox") && !args.IsArgNegated("-sandbox")) {
+        const std::string sandbox_arg{args.GetArg("-sandbox", "")};
+        bool log_syscall_violation_before_terminating{false};
+        if (sandbox_arg == "log-and-abort") {
+            log_syscall_violation_before_terminating = true;
+        } else if (sandbox_arg == "abort") {
+            // log_syscall_violation_before_terminating is false by default.
+        } else {
+            return InitError(Untranslated("Unknown syscall sandbox mode (-sandbox=<mode>). Available modes are \"log-and-abort\" and \"abort\"."));
+        }
+        // execve(...) is not allowed by the syscall sandbox.
+        const std::vector<std::string> features_using_execve{
+            "-alertnotify",
+            "-blocknotify",
+            "-signer",
+            "-startupnotify",
+            "-walletnotify",
+        };
+        for (const std::string& feature_using_execve : features_using_execve) {
+            if (!args.GetArg(feature_using_execve, "").empty()) {
+                return InitError(Untranslated(strprintf("The experimental syscall sandbox feature (-sandbox=<mode>) is incompatible with %s (which uses execve).", feature_using_execve)));
+            }
+        }
+        if (!SetupSyscallSandbox(log_syscall_violation_before_terminating)) {
+            return InitError(Untranslated("Installation of the syscall sandbox failed."));
+        }
+        LogPrintf("Experimental syscall sandbox enabled (-sandbox=%s): bitcoind will terminate if an unexpected (not allowlisted) syscall is invoked.\n", sandbox_arg);
+    }
+#endif // USE_SYSCALL_SANDBOX
+
     return true;
 }
 

src/logging.cpp

@@ -160,6 +160,7 @@ const CLogCategoryDesc LogCategories[] =
     {BCLog::I2P, "i2p"},
     {BCLog::IPC, "ipc"},
     {BCLog::LOCK, "lock"},
+    {BCLog::UTIL, "util"},
     {BCLog::ALL, "1"},
     {BCLog::ALL, "all"},
 };

src/logging.h

@@ -60,6 +60,7 @@ namespace BCLog {
         I2P         = (1 << 22),
         IPC         = (1 << 23),
         LOCK        = (1 << 24),
+        UTIL        = (1 << 25),
         ALL         = ~(uint32_t)0,
     };