src: reset SIGSEGV handler before crashing

Without this, we would re-enter the signal handler immediately
after re-raising the signal, leading to an infinite loop.

PR-URL: https://github.com/nodejs/node/pull/27775
Refs: https://github.com/nodejs/node/pull/27246
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

src/node.cc

@@ -487,6 +487,12 @@ void TrapWebAssemblyOrContinue(int signo, siginfo_t* info, void* ucontext) {
     if (prev != nullptr) {
       prev(signo, info, ucontext);
     } else {
+      // Reset to the default signal handler, i.e. cause a hard crash.
+      struct sigaction sa;
+      memset(&sa, 0, sizeof(sa));
+      sa.sa_handler = SIG_DFL;
+      CHECK_EQ(sigaction(signo, &sa, nullptr), 0);
+
       ResetStdio();
       raise(signo);
     }

src/node_process_methods.cc

@@ -63,6 +63,12 @@ static void Abort(const FunctionCallbackInfo<Value>& args) {
   Abort();
 }
 
+// For internal testing only, not exposed to userland.
+static void CauseSegfault(const FunctionCallbackInfo<Value>& args) {
+  // This should crash hard all platforms.
+  *static_cast<void**>(nullptr) = nullptr;
+}
+
 static void Chdir(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
   CHECK(env->owns_process_state());
@@ -405,6 +411,7 @@ static void InitializeProcessMethods(Local<Object> target,
     env->SetMethod(target, "_debugProcess", DebugProcess);
     env->SetMethod(target, "_debugEnd", DebugEnd);
     env->SetMethod(target, "abort", Abort);
+    env->SetMethod(target, "causeSegfault", CauseSegfault);
     env->SetMethod(target, "chdir", Chdir);
   }
 

test/abort/test-signal-handler.js

@@ -0,0 +1,23 @@
+'use strict';
+const common = require('../common');
+if (common.isWindows)
+  common.skip('No signals on Window');
+
+const assert = require('assert');
+const { spawnSync } = require('child_process');
+
+// Test that a hard crash does not cause an endless loop.
+
+if (process.argv[2] === 'child') {
+  const { internalBinding } = require('internal/test/binding');
+  const { causeSegfault } = internalBinding('process_methods');
+
+  causeSegfault();
+} else {
+  const child = spawnSync(process.execPath,
+                          ['--expose-internals', __filename, 'child'],
+                          { stdio: 'inherit' });
+  // FreeBSD and macOS use SIGILL for the kind of crash we're causing here.
+  assert(child.signal === 'SIGSEGV' || child.signal === 'SIGILL',
+         `child.signal = ${child.signal}`);
+}