buffer: fix lastIndexOf crash for overlong needle

Return -1 in `Buffer.lastIndexOf` if the needle is longer than the
haystack. The previous check only tested the corresponding
condition for forward searches.

This applies only to Node.js v6, as `lastIndexOf` was added in it.

Fixes: nodejs#6510

Author: addaleax

src/node_buffer.cc

@@ -1011,7 +1011,8 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
   }
   size_t offset = static_cast<size_t>(opt_offset);
   CHECK_LT(offset, haystack_length);
-  if (is_forward && needle_length + offset > haystack_length) {
+  if ((is_forward && needle_length + offset > haystack_length) ||
+      needle_length > haystack_length) {
     return args.GetReturnValue().Set(-1);
   }
 
@@ -1113,7 +1114,8 @@ void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
   }
   size_t offset = static_cast<size_t>(opt_offset);
   CHECK_LT(offset, haystack_length);
-  if (is_forward && needle_length + offset > haystack_length) {
+  if ((is_forward && needle_length + offset > haystack_length) ||
+      needle_length > haystack_length) {
     return args.GetReturnValue().Set(-1);
   }
 

test/parallel/test-buffer-indexof.js

@@ -354,12 +354,35 @@ assert.equal(b.lastIndexOf('b', {}), 1);
 assert.equal(b.lastIndexOf('b', []), -1);
 assert.equal(b.lastIndexOf('b', [2]), 1);
 
+// Test needles longer than the haystack.
+assert.strictEqual(b.lastIndexOf('aaaaaaaaaaaaaaa', 'ucs2'), -1);
+assert.strictEqual(b.lastIndexOf('aaaaaaaaaaaaaaa', 'utf8'), -1);
+assert.strictEqual(b.lastIndexOf('aaaaaaaaaaaaaaa', 'binary'), -1);
+assert.strictEqual(b.lastIndexOf(Buffer.from('aaaaaaaaaaaaaaa')), -1);
+assert.strictEqual(b.lastIndexOf('aaaaaaaaaaaaaaa', 2, 'ucs2'), -1);
+assert.strictEqual(b.lastIndexOf('aaaaaaaaaaaaaaa', 3, 'utf8'), -1);
+assert.strictEqual(b.lastIndexOf('aaaaaaaaaaaaaaa', 5, 'binary'), -1);
+assert.strictEqual(b.lastIndexOf(Buffer.from('aaaaaaaaaaaaaaa'), 7), -1);
+
+// 你好 expands to a total of 6 bytes using UTF-8 and 4 bytes using UTF-16
+assert.strictEqual(buf_bc.lastIndexOf('你好', 'ucs2'), -1);
+assert.strictEqual(buf_bc.lastIndexOf('你好', 'utf8'), -1);
+assert.strictEqual(buf_bc.lastIndexOf('你好', 'binary'), -1);
+assert.strictEqual(buf_bc.lastIndexOf(Buffer.from('你好')), -1);
+assert.strictEqual(buf_bc.lastIndexOf('你好', 2, 'ucs2'), -1);
+assert.strictEqual(buf_bc.lastIndexOf('你好', 3, 'utf8'), -1);
+assert.strictEqual(buf_bc.lastIndexOf('你好', 5, 'binary'), -1);
+assert.strictEqual(buf_bc.lastIndexOf(Buffer.from('你好'), 7), -1);
+
 // Test lastIndexOf on a longer buffer:
 var bufferString = new Buffer('a man a plan a canal panama');
 assert.equal(15, bufferString.lastIndexOf('canal'));
 assert.equal(21, bufferString.lastIndexOf('panama'));
 assert.equal(0, bufferString.lastIndexOf('a man a plan a canal panama'));
 assert.equal(-1, bufferString.lastIndexOf('a man a plan a canal mexico'));
+assert.equal(-1, bufferString.lastIndexOf('a man a plan a canal mexico city'));
+assert.equal(-1, bufferString.lastIndexOf(Buffer.from('a'.repeat(1000))));
+assert.equal(0, bufferString.lastIndexOf('a man a plan', 4));
 assert.equal(13, bufferString.lastIndexOf('a '));
 assert.equal(13, bufferString.lastIndexOf('a ', 13));
 assert.equal(6, bufferString.lastIndexOf('a ', 12));