msg/async/ProtocolV2: avoid AES-GCM nonce reuse vulnerabilities

The secure mode uses AES-128-GCM with 96-bit nonces consisting of a
32-bit counter followed by a 64-bit salt.  The counter is incremented
after processing each frame, the salt is fixed for the duration of
the session.  Both are initialized from the session key generated
during session negotiation, so the counter starts with essentially
a random value.  It is allowed to wrap, and, after 2**32 frames, it
repeats, resulting in nonce reuse (the actual sequence numbers that
the messenger works with are 64-bit, so the session continues on).

Because of how GCM works, this completely breaks both confidentiality
and integrity aspects of the secure mode.  A single nonce reuse reveals
the XOR of two plaintexts and almost completely reveals the subkey
used for producing authentication tags.  After a few nonces get used
twice, all confidentiality and integrity goes out the window and the
attacker can potentially encrypt-authenticate plaintext of their
choice.

We can't easily change the nonce format to extend the counter to
64 bits (and possibly XOR it with a longer salt).  Instead, just
remember the initial nonce and cut the session before it repeats,
forcing renegotiation.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Radoslaw Zarzynski <rzarzyns@redhat.com>
Reviewed-by: Sage Weil <sage@redhat.com>
Conflicts:
	src/msg/async/ProtocolV2.h [ context: commit ed3ec4c01d17
	  ("msg: Build target 'common' without using namespace in
	  headers") not in octopus ]

diff --git a/src/msg/async/ProtocolV2.cc b/src/msg/async/ProtocolV2.cc
index 8fc02db6e559a24616dbe49afe0daaca23a95306..c69f2ccf79ad26cca248f6ed1dd9c7ce2ae351a4 100644 (file)
--- a/src/msg/async/ProtocolV2.cc
+++ b/src/msg/async/ProtocolV2.cc
@@ -533,7 +533,10 @@ ssize_t ProtocolV2::write_message(Message *m, bool more) {
                             m->get_payload(),
                             m->get_middle(),
                             m->get_data());
-  connection->outgoing_bl.append(message.get_buffer(session_stream_handlers));
+  if (!append_frame(message)) {
+    m->put();
+    return -EILSEQ;
+  }
 
   ldout(cct, 5) << __func__ << " sending message m=" << m
                 << " seq=" << m->get_seq() << " " << *m << dendl;
@@ -566,15 +569,17 @@ ssize_t ProtocolV2::write_message(Message *m, bool more) {
   return rc;
 }
 
-void ProtocolV2::append_keepalive() {
-  ldout(cct, 10) << __func__ << dendl;
-  auto keepalive_frame = KeepAliveFrame::Encode();
-  connection->outgoing_bl.append(keepalive_frame.get_buffer(session_stream_handlers));
-}
-
-void ProtocolV2::append_keepalive_ack(utime_t &timestamp) {
-  auto keepalive_ack_frame = KeepAliveFrameAck::Encode(timestamp);
-  connection->outgoing_bl.append(keepalive_ack_frame.get_buffer(session_stream_handlers));
+template <class F>
+bool ProtocolV2::append_frame(F& frame) {
+  ceph::bufferlist bl;
+  try {
+    bl = frame.get_buffer(session_stream_handlers);
+  } catch (ceph::crypto::onwire::TxHandlerError &e) {
+    ldout(cct, 1) << __func__ << " " << e.what() << dendl;
+    return false;
+  }
+  connection->outgoing_bl.append(bl);
+  return true;
 }
 
 void ProtocolV2::handle_message_ack(uint64_t seq) {
@@ -612,7 +617,15 @@ void ProtocolV2::write_event() {
   connection->write_lock.lock();
   if (can_write) {
     if (keepalive) {
-      append_keepalive();
+      ldout(cct, 10) << __func__ << " appending keepalive" << dendl;
+      auto keepalive_frame = KeepAliveFrame::Encode();
+      if (!append_frame(keepalive_frame)) {
+        connection->write_lock.unlock();
+        connection->lock.lock();
+        fault();
+        connection->lock.unlock();
+        return;
+      }
       keepalive = false;
     }
 
@@ -663,13 +676,16 @@ void ProtocolV2::write_event() {
     if (r == 0) {
       uint64_t left = ack_left;
       if (left) {
-        auto ack = AckFrame::Encode(in_seq);
-        connection->outgoing_bl.append(ack.get_buffer(session_stream_handlers));
         ldout(cct, 10) << __func__ << " try send msg ack, acked " << left
                        << " messages" << dendl;
-        ack_left -= left;
-        left = ack_left;
-        r = connection->_try_send(left);
+        auto ack_frame = AckFrame::Encode(in_seq);
+        if (append_frame(ack_frame)) {
+          ack_left -= left;
+          left = ack_left;
+          r = connection->_try_send(left);
+        } else {
+          r = -EILSEQ;
+        }
       } else if (is_queued()) {
         r = connection->_try_send();
       }
@@ -769,7 +785,13 @@ template <class F>
 CtPtr ProtocolV2::write(const std::string &desc,
                         CONTINUATION_TYPE<ProtocolV2> &next,
                         F &frame) {
-  ceph::bufferlist bl = frame.get_buffer(session_stream_handlers);
+  ceph::bufferlist bl;
+  try {
+    bl = frame.get_buffer(session_stream_handlers);
+  } catch (ceph::crypto::onwire::TxHandlerError &e) {
+    ldout(cct, 1) << __func__ << " " << e.what() << dendl;
+    return _fault();
+  }
   return write(desc, next, bl);
 }
 
@@ -1672,7 +1694,11 @@ CtPtr ProtocolV2::handle_keepalive2(ceph::bufferlist &payload)
   ldout(cct, 30) << __func__ << " got KEEPALIVE2 tag ..." << dendl;
 
   connection->write_lock.lock();
-  append_keepalive_ack(keepalive_frame.timestamp());
+  auto keepalive_ack_frame = KeepAliveFrameAck::Encode(keepalive_frame.timestamp());
+  if (!append_frame(keepalive_ack_frame)) {
+    connection->write_lock.unlock();
+    return _fault();
+  }
   connection->write_lock.unlock();
 
   ldout(cct, 20) << __func__ << " got KEEPALIVE2 "

diff --git a/src/msg/async/ProtocolV2.h b/src/msg/async/ProtocolV2.h
index 2dbe647ae546f5c50b60f7a5c19d969eedd28977..9897d18cf23334d9d81a349c3a085462b1348302 100644 (file)
--- a/src/msg/async/ProtocolV2.h
+++ b/src/msg/async/ProtocolV2.h
@@ -129,6 +129,9 @@ private:
                         CONTINUATION_TYPE<ProtocolV2> &next,
                         bufferlist &buffer);
 
+  template <class F>
+  bool append_frame(F& frame);
+
   void requeue_sent();
   uint64_t discard_requeued_up_to(uint64_t out_seq, uint64_t seq);
   void reset_recv_state();
@@ -140,8 +143,6 @@ private:
   void prepare_send_message(uint64_t features, Message *m);
   out_queue_entry_t _get_next_outgoing();
   ssize_t write_message(Message *m, bool more);
-  void append_keepalive();
-  void append_keepalive_ack(utime_t &timestamp);
   void handle_message_ack(uint64_t seq);
 
   CONTINUATION_DECL(ProtocolV2, _wait_for_peer_banner);

diff --git a/src/msg/async/crypto_onwire.cc b/src/msg/async/crypto_onwire.cc
index acf3f66689e14cbd816911945660cfc75b2c0d0f..07e7fe6553c2bda047518e959650dd9f257cd3a0 100644 (file)
--- a/src/msg/async/crypto_onwire.cc
+++ b/src/msg/async/crypto_onwire.cc
@@ -22,6 +22,10 @@ static constexpr const std::size_t AESGCM_BLOCK_LEN{16};
 struct nonce_t {
   std::uint32_t random_seq;
   std::uint64_t random_rest;
+
+  bool operator==(const nonce_t& rhs) const {
+    return !memcmp(this, &rhs, sizeof(*this));
+  }
 } __attribute__((packed));
 static_assert(sizeof(nonce_t) == AESGCM_IV_LEN);
 
@@ -35,7 +39,8 @@ class AES128GCM_OnWireTxHandler : public ceph::crypto::onwire::TxHandler {
   CephContext* const cct;
   std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)> ectx;
   ceph::bufferlist buffer;
-  nonce_t nonce;
+  nonce_t nonce, initial_nonce;
+  bool used_initial_nonce;
   static_assert(sizeof(nonce) == AESGCM_IV_LEN);
 
 public:
@@ -44,7 +49,7 @@ public:
                            const nonce_t& nonce)
     : cct(cct),
       ectx(EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free),
-      nonce(nonce) {
+      nonce(nonce), initial_nonce(nonce), used_initial_nonce(false) {
     ceph_assert_always(ectx);
     ceph_assert_always(key.size() * CHAR_BIT == 128);
 
@@ -61,6 +66,7 @@ public:
 
   ~AES128GCM_OnWireTxHandler() override {
     ::ceph::crypto::zeroize_for_security(&nonce, sizeof(nonce));
+    ::ceph::crypto::zeroize_for_security(&initial_nonce, sizeof(initial_nonce));
   }
 
   std::uint32_t calculate_segment_size(std::uint32_t size) override
@@ -78,6 +84,13 @@ public:
 void AES128GCM_OnWireTxHandler::reset_tx_handler(
   std::initializer_list<std::uint32_t> update_size_sequence)
 {
+  if (nonce == initial_nonce) {
+    if (used_initial_nonce) {
+      throw ceph::crypto::onwire::TxHandlerError("out of nonces");
+    }
+    used_initial_nonce = true;
+  }
+
   if(1 != EVP_EncryptInit_ex(ectx.get(), nullptr, nullptr, nullptr,
       reinterpret_cast<const unsigned char*>(&nonce))) {
     throw std::runtime_error("EVP_EncryptInit_ex failed");

diff --git a/src/msg/async/crypto_onwire.h b/src/msg/async/crypto_onwire.h
index bd682e8c71cde49220c0bc3fae2941e7f549adb9..0c544f205aca468144315dddc9f3695b67fc5364 100644 (file)
--- a/src/msg/async/crypto_onwire.h
+++ b/src/msg/async/crypto_onwire.h
@@ -45,6 +45,11 @@ struct MsgAuthError : public std::runtime_error {
   }
 };
 
+struct TxHandlerError : public std::runtime_error {
+  TxHandlerError(const char* what)
+    : std::runtime_error(std::string("tx handler error: ") + what) {}
+};
+
 struct TxHandler {
   virtual ~TxHandler() = default;