security: replace unsafe /X+$/ idiom with rtrim

Problem:
replace(/X+$/, '') is vulnerable to REDOS

Solution:
Replace all instances I could find with a custom rtrim

Author: davisjam

lib/marked.js

@@ -4,6 +4,38 @@
  * https://github.com/markedjs/marked
  */
 
+// Return str with all trailing {c | all but c} removed
+// allButC: Default false
+function rtrim(str, c, allButC) {
+  if (typeof allButC === 'undefined') {
+    allButC = false;
+  } else {
+    allButC = true;
+  }
+  var mustMatchC = !allButC;
+
+  if (str.length === 0) {
+    return '';
+  }
+
+  // ix+1 of leftmost that fits description
+  // i.e. the length of the string we should return
+  var curr = str.length;
+
+  while (curr > 0) {
+    var currChar = str.charAt(curr - 1);
+    if (mustMatchC && currChar === c) {
+      curr--;
+    } else if (!mustMatchC && currChar !== c) {
+      curr--;
+    } else {
+      break;
+    }
+  }
+
+  return str.substr(0, curr);
+}
+
 ;(function(root) {
 'use strict';
 
@@ -216,7 +248,7 @@ Lexer.prototype.token = function(src, top) {
       this.tokens.push({
         type: 'code',
         text: !this.options.pedantic
-          ? cap.replace(/\n+$/, '')
+          ? rtrim(cap, '\n')
           : cap
       });
       continue;
@@ -238,15 +270,11 @@ Lexer.prototype.token = function(src, top) {
       src = src.substring(cap[0].length);
       // cap[2] might be ' HEADING # '
       item = (cap[2] || '').trim();
-      if (item.slice(-1) === '#') {
-        // NB replace(/#+$/) is quadratic on mismatch because it's unanchored,
-        // so we protect with if-check to ensure it won't mismatch.
-        if (this.options.pedantic) {
-          item = item.replace(/#+$/, '');
-        } else {
-          // CM requires a space before additional #s
-          item = item.replace(/(\s|^)#+$/, '');
-        }
+      if (this.options.pedantic) {
+        item = rtrim(item, '#');
+      } else {
+        // CM requires a space before additional #s
+        item = item.replace(/(\s|^)#+$/, '');
       }
       item = item.trim();
       this.tokens.push({
@@ -1288,7 +1316,7 @@ function resolveUrl(base, href) {
     if (/^[^:]+:\/*[^/]*$/.test(base)) {
       baseUrls[' ' + base] = base + '/';
     } else {
-      baseUrls[' ' + base] = base.replace(/[^/]*$/, '');
+      baseUrls[' ' + base] = rtrim(base, '/', true);
     }
   }
   base = baseUrls[' ' + base];