fix(jsbn): prevent modInverse hang for zero input

Author: Kr0emer

lib/jsbn.js

@@ -1122,6 +1122,7 @@ function bnpModInt(n) {
 
 // (public) 1/this % m (HAC 14.61)
 function bnModInverse(m) {
+  if(this.signum() == 0) return BigInteger.ZERO;
   var ac = m.isEven();
   if((this.isEven() && ac) || m.signum() == 0) return BigInteger.ZERO;
   var u = m.clone(), v = this.clone();

tests/unit/index.js

@@ -1,4 +1,5 @@
 require('./forge');
+require('./jsbn');
 require('./util');
 require('./md5');
 require('./sha1');

tests/unit/jsbn.js

@@ -0,0 +1,45 @@
+var ASSERT = require('assert');
+
+(function() {
+  if(typeof process === 'undefined' ||
+    !process.versions || !process.versions.node) {
+    return;
+  }
+
+  var moduleRequire = module.require ? module.require.bind(module) : require;
+  var PATH = moduleRequire('path');
+  var spawnSync = moduleRequire('child_process').spawnSync;
+
+  describe('jsbn', function() {
+    it('should return 0 for BigInteger(0).modInverse(3) without hanging', function() {
+      var script = [
+        'var JSBN = require("./lib/jsbn");',
+        'var BigInteger = JSBN.BigInteger;',
+        'var zero = new BigInteger("0", 10);',
+        'var mod = new BigInteger("3", 10);',
+        'var inv = zero.modInverse(mod);',
+        'process.stdout.write(inv.toString());'
+      ].join('\n');
+
+      var result = spawnSync(process.execPath, ['-e', script], {
+        cwd: PATH.join(__dirname, '../..'),
+        encoding: 'utf8',
+        timeout: 2000
+      });
+
+      if(result.error) {
+        if(result.error.code === 'EPERM') {
+          this.skip();
+          return;
+        }
+        if(result.error.code === 'ETIMEDOUT') {
+          ASSERT.fail('BigInteger(0).modInverse(3) timed out.');
+        }
+        throw result.error;
+      }
+
+      ASSERT.equal(result.status, 0, result.stderr);
+      ASSERT.equal(result.stdout, '0');
+    });
+  });
+})();