Add a buffer reader/writer for NTLM.

net/http/ntlm_buffer_reader.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_BASE_NTLM_BUFFER_READER_H_
+#define NET_BASE_NTLM_BUFFER_READER_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <string>
+
+#include "base/strings/string_piece.h"
+#include "net/base/net_export.h"
+#include "net/http/ntlm.h"
+
+namespace net {
+
+// Supports various bounds-checked low level buffer operations required by an
+// NTLM implementation.
+//
+// The class supports sequential read of a provided buffer. All reads perform
+// bounds checking to ensure enough space is remaining in the buffer.
+//
+// Read* methods read from the buffer at the current cursor position and
+// perform any necessary type conversion and provide the data in out params.
+// After a successful read the cursor position is advanced past the read
+// field.
+//
+// Failed reads leave the internal cursor at the same position as before the
+// call.
+//
+// Read*Payload methods first reads a security buffer (see
+// |ReadSecurityBuffer|), then reads the requested payload from the offset
+// and length stated in the security buffer.
+//
+// If the length and offset in the security buffer would cause a read outside
+// the message buffer the payload will not be read and the function will
+// return false.
+//
+// Based on [MS-NLMP]: NT LAN Manager (NTLM) Authentication Protocol
+// Specification version 28.0 [1]
+//
+// [1] https://msdn.microsoft.com/en-us/library/cc236621.aspx
+class NET_EXPORT_PRIVATE NtlmBufferReader {
+ public:
+  explicit NtlmBufferReader(base::StringPiece buffer);
+
+  // This class does not take ownership of |ptr| so the caller must ensure
+  // that the buffer outlives the |NtlmBufferReader|.
+  NtlmBufferReader(const uint8_t* ptr, size_t len);
+  ~NtlmBufferReader();
+
+  size_t GetLength() const { return buffer_.length(); }
+  size_t GetCursor() const { return cursor_; }
+  bool IsEndOfBuffer() const { return cursor_ >= GetLength(); }
+
+  // Returns true if there are |len| more bytes between the current cursor
+  // position and the end of the buffer.
+  bool CanRead(size_t len) const;
+
+  // Returns true if there are |len| more bytes between |offset| and the end
+  // of the buffer. The cursor position is not used or modified.
+  bool CanReadFrom(size_t offset, size_t len) const;
+
+  // Returns true if it would be possible to read the payload described by the
+  // security buffer.
+  bool CanReadFrom(ntlm::SecurityBuffer sec_buf) const {
+    return CanReadFrom(sec_buf.offset, sec_buf.length);
+  }
+
+  // Reads a 16 bit value (little endian) as a uint16_t. If there are not 16
+  // more bits available it returns false.
+  bool ReadUInt16(uint16_t* value);

[asanka, 2017/06/16 03:21:29]

To be pedantic, the Read*s, Skip*s, and Write*s should be annotated with
WARN_UNUSED_RESULT.

[zentaro, 2017/06/21 00:38:47]

Done.

+
+  // Reads a 32 bit value (little endian) as a uint32_t. If there are not 32
+  // more bits available it returns false.
+  bool ReadUInt32(uint32_t* value);
+
+  // Reads a 64 bit value (little endian) as a uint64_t. If there are not 64
+  // more bits available it returns false.
+  bool ReadUInt64(uint64_t* value);
+
+  // Calls |ReadUInt32| and returns it cast as |NegotiateFlags|. No
+  // validation of the value takes place.
+  bool ReadFlags(ntlm::NegotiateFlags* flags);
+
+  // Reads |len| bytes and copies them into |buffer|.
+  bool ReadBytes(uint8_t* buffer, size_t len);
+
+  // A security buffer is an 8 byte structure that defines the offset and
+  // length of a payload (string, struct or byte array) that appears after the
+  // fixed part of the message.
+  //
+  // The structure is (little endian fields):
+  //     uint16 - |length| Length of payload
+  //     uint16 - Allocation (this is always ignored and not returned)
+  //     uint32 - |offset| Offset from start of message
+  bool ReadSecurityBuffer(ntlm::SecurityBuffer* sec_buf);
+
+  // Reads |len| bytes into the std::string value. Technically these are
+  // actually in the OEM character set. In practice the implementation
+  // just treats any of these strings as an opaque byte sequence.
+  bool ReadUtf8String(std::string* value, size_t len);
+
+  // Reads |len| bytes as a UTF-16 string with little-endian byte order.
+  bool ReadUtf16String(base::string16* value, size_t len);
+
+  // There are 3 message types Negotiate (sent by client), Challenge (sent by
+  // server), and Authenticate (sent by client).
+  //
+  // This reads the message type from the header and will return false if the
+  // value is invalid.
+  bool ReadMessageType(ntlm::MessageType* message_type);
+
+  // First reads a security buffer (see |ReadSecurityBuffer|), then verifies
+  // that the offset and length it states are within the message, then
+  // reads those bytes from the payload part of the message into a
+  // std::string.
+  //
+  // If the security buffer can't be read or the values in the security buffer
+  // are outside the bounds of the message then false will be returned.
+  //
+  // In the case of failure the cursor will remain as if it never read the
+  // security buffer. In the case of success the cursor will point after the
+  // security buffer.
+  //
+  // NOTE: Technically in NTLM 8-bit strings are in the OEM character set,
+  // however we never try to interpret these strings as anything other than
+  // a sequence of bytes, so the actual encoding is not relevant.
+  bool ReadUtf8Payload(std::string* value);

[asanka, 2017/06/16 03:21:29]

Yeah, I was only referring to the Write* cases when I recommended always
sticking with UTF 8. The Read* case is different in that we shouldn't do
anything that relies on the buffer being valid UTF-8. Apologies if there was a
miscommunication.

For the Read* cases, it should be evident from the callsite that we are reading
an octet stream of unknown encoding. I don't think even the UTF-16 version is
safe in that it could still be invalid UTF-16.

I think we can get away with not interpreting these strings, right? If so, let's
stick to the ReadBytes*() and SkipBytes*() stuff and not introduce a dangerous
API.

[zentaro, 2017/06/21 00:38:47]

Read*String and Read*StringPayload methods were only actually used by tests to
validate the content of messages we generated. So I removed them all since the
actual implementation never needs to interpret these payloads. In the next CL I
just added helpers to the test code to simplify the validation.

+
+  // Reads a security buffer (see |ReadSecurityBuffer|), then verifies
+  // that the offset and length it states are within the message, then
+  // reads those bytes from the payload part of the message into a
+  // base::string16. The 16 bit characters within the string are read
+  // little endian.
+  //
+  // If the security buffer can't be read or the values in the security buffer
+  // are outside the bounds of the message then false will be returned.
+  //
+  // In the case of failure the cursor will remain as if it never read the
+  // security buffer. In the case of success the cursor will point after the
+  // security buffer.
+  bool ReadUtf16Payload(base::string16* value);
+
+  // First reads a security buffer (see |ReadSecurityBuffer|), then verifies
+  // that the offset and length it states are within the message, then
+  // reads those bytes from the payload and copies them into the provided
+  // |buffer|.
+  //
+  // If the security buffer can't be read or the values in the security buffer
+  // are outside the bounds of the message or |buffer_len| is less than the
+  // size of the payload then false will be returned.
+  //
+  // In the case of failure the cursor will remain as if it never read the
+  // security buffer. In the case of success the cursor will point after the
+  // security buffer.
+  bool ReadBytesPayload(uint8_t* buffer, size_t buffer_len);
+
+  // Skips over a security buffer field without reading the fields. This is
+  // the equivalent of advancing the cursor 8 bytes. Returns false if there
+  // are less than 8 bytes left in the buffer.
+  bool SkipSecurityBuffer();
+
+  // Skips over the security buffer without returning the values, but fails if
+  // the values would cause a read outside the buffer if the payload was
+  // actually read.
+  bool SkipSecurityBufferWithValidation();
+
+  // Skips over |count| bytes in the buffer. Returns false if there is not
+  // |count| bytes left in the buffer.
+  bool SkipBytes(size_t count);
+
+  // Reads and returns true if the next 8 bytes matches the signature in an
+  // NTLM message "NTLMSSP\0". The cursor advances if the the signature
+  // is matched.
+  bool MatchSignature();
+
+  // Performs |ReadMessageType| and returns true if the value is
+  // |message_type|. If the read fails or the message type does not match
+  // the cursor does not move.
+  bool MatchMessageType(ntlm::MessageType message_type);
+
+  // Performs |MatchSignature| then |MatchMessageType|.
+  bool MatchMessageHeader(ntlm::MessageType message_type);
+
+  // Performs |ReadBytes(count)| and returns true if the contents is all
+  // zero.
+  bool MatchZeros(size_t count);
+
+  // Reads and returns true if the next 8 bytes contain an empty ie. all zero
+  // security buffer. If the read fails or the message type does not match
+  // the cursor does not move.
+  bool MatchEmptySecurityBuffer();
+
+ private:
+  // Reads |sizeof(T)| bytes of an integer type from a little-endian buffer.
+  template <typename T>
+  bool ReadUInt(T* value);
+
+  // Sets the cursor position. This is used when reading payloads to move the
+  // cursor to the start of the payload indicated by the security buffer.
+  // The caller should use |GetLength|, |CanRead|, or |CanReadFrom| to verify
+  // the bounds before calling this method.
+  void SetCursor(size_t cursor);
+
+  // Advances the cursor by |count| bytes. The caller should use|GetLength|,
+  // |CanRead|, or |CanReadFrom| to verify the bounds before calling this
+  // method.
+  void AdvanceCursor(size_t count) { SetCursor(GetCursor() + count); }
+
+  // Returns a constant pointer to the start of the buffer.
+  const uint8_t* GetBufferPtr() const {
+    return reinterpret_cast<const uint8_t*>(buffer_.data());
+  }
+
+  // Returns a pointer to the underlying buffer at the current cursor
+  // position.
+  const uint8_t* GetBufferAtCursor() const { return GetBufferPtr() + cursor_; }
+
+  // Returns the byte at the current cursor position.
+  uint8_t GetByteAtCursor() const {
+    DCHECK(!IsEndOfBuffer());
+    return *(GetBufferAtCursor());
+  }
+
+  const base::StringPiece buffer_;
+  size_t cursor_;
+
+  DISALLOW_COPY_AND_ASSIGN(NtlmBufferReader);
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_NTLM_BUFFER_READER_H_