1 files changed, 276 insertions, 0 deletions
diff --git a/security/nss/lib/ssl/tls13replay.c b/security/nss/lib/ssl/tls13replay.c
new file mode 100644
index 0000000000..b090f9bca7
--- /dev/null
+++ b/security/nss/lib/ssl/tls13replay.c
@@ -0,0 +1,276 @@
+/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * Anti-replay measures for TLS 1.3.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nss.h"      /* for NSS_RegisterShutdown */
+#include "nssilock.h" /* for PZMonitor */
+#include "pk11pub.h"
+#include "prinit.h" /* for PR_CallOnce */
+#include "prmon.h"
+#include "prtime.h"
+#include "secerr.h"
+#include "ssl.h"
+#include "sslbloom.h"
+#include "sslimpl.h"
+#include "tls13hkdf.h"
+
+static struct {
+    /* Used to ensure that we only initialize the cleanup function once. */
+    PRCallOnceType init;
+    /* Used to serialize access to the filters. */
+    PZMonitor *lock;
+    /* The filters, use of which alternates. */
+    sslBloomFilter filters[2];
+    /* Which of the two filters is active (0 or 1). */
+    PRUint8 current;
+    /* The time that we will next update. */
+    PRTime nextUpdate;
+    /* The width of the window; i.e., the period of updates. */
+    PRTime window;
+    /* This key ensures that the bloom filter index is unpredictable. */
+    PK11SymKey *key;
+} ssl_anti_replay;
+
+/* Clear the current state and free any resources we allocated. The signature
+ * here is odd to allow this to be called during shutdown. */
+static SECStatus
+tls13_AntiReplayReset(void *appData, void *nssData)
+{
+    if (ssl_anti_replay.key) {
+        PK11_FreeSymKey(ssl_anti_replay.key);
+        ssl_anti_replay.key = NULL;
+    }
+    if (ssl_anti_replay.lock) {
+        PZ_DestroyMonitor(ssl_anti_replay.lock);
+        ssl_anti_replay.lock = NULL;
+    }
+    sslBloom_Destroy(&ssl_anti_replay.filters[0]);
+    sslBloom_Destroy(&ssl_anti_replay.filters[1]);
+    return SECSuccess;
+}
+
+static PRStatus
+tls13_AntiReplayInit(void)
+{
+    SECStatus rv = NSS_RegisterShutdown(tls13_AntiReplayReset, NULL);
+    if (rv != SECSuccess) {
+        return PR_FAILURE;
+    }
+    return PR_SUCCESS;
+}
+
+static SECStatus
+tls13_AntiReplayKeyGen()
+{
+    PRUint8 buf[32];
+    SECItem keyItem = { siBuffer, buf, sizeof(buf) };
+    PK11SlotInfo *slot;
+    SECStatus rv;
+
+    slot = PK11_GetInternalSlot();
+    if (!slot) {
+        PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);
+        return SECFailure;
+    }
+    rv = PK11_GenerateRandomOnSlot(slot, buf, sizeof(buf));
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    ssl_anti_replay.key = PK11_ImportSymKey(slot, CKM_NSS_HKDF_SHA256,
+                                            PK11_OriginUnwrap, CKA_DERIVE,
+                                            &keyItem, NULL);
+    if (!ssl_anti_replay.key) {
+        goto loser;
+    }
+
+    PK11_FreeSlot(slot);
+    return SECSuccess;
+
+loser:
+    PK11_FreeSlot(slot);
+    return SECFailure;
+}
+
+/* Set a limit on the combination of number of hashes and bits in each hash. */
+#define SSL_MAX_BLOOM_FILTER_SIZE 64
+
+/*
+ * The structures created by this function can be called concurrently on
+ * multiple threads if the server is multi-threaded.  A monitor is used to
+ * ensure that only one thread can access the structures that change over time,
+ * but no such guarantee is provided for configuration data.
+ *
+ * Functions that read from static configuration data depend on there being a
+ * memory barrier between the setup and use of this function.
+ */
+SECStatus
+SSLExp_SetupAntiReplay(PRTime window, unsigned int k, unsigned int bits)
+{
+    SECStatus rv;
+
+    if (k == 0 || bits == 0) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+    if ((k * (bits + 7) / 8) > SSL_MAX_BLOOM_FILTER_SIZE) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    if (PR_SUCCESS != PR_CallOnce(&ssl_anti_replay.init,
+                                  tls13_AntiReplayInit)) {
+        PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);
+        return SECFailure;
+    }
+
+    (void)tls13_AntiReplayReset(NULL, NULL);
+
+    ssl_anti_replay.lock = PZ_NewMonitor(nssILockSSL);
+    if (!ssl_anti_replay.lock) {
+        goto loser; /* Code already set. */
+    }
+
+    rv = tls13_AntiReplayKeyGen();
+    if (rv != SECSuccess) {
+        goto loser; /* Code already set. */
+    }
+
+    rv = sslBloom_Init(&ssl_anti_replay.filters[0], k, bits);
+    if (rv != SECSuccess) {
+        goto loser; /* Code already set. */
+    }
+    rv = sslBloom_Init(&ssl_anti_replay.filters[1], k, bits);
+    if (rv != SECSuccess) {
+        goto loser; /* Code already set. */
+    }
+    /* When starting out, ensure that 0-RTT is not accepted until the window is
+     * updated.  A ClientHello might have been accepted prior to a restart. */
+    sslBloom_Fill(&ssl_anti_replay.filters[1]);
+
+    ssl_anti_replay.current = 0;
+    ssl_anti_replay.nextUpdate = ssl_TimeUsec() + window;
+    ssl_anti_replay.window = window;
+    return SECSuccess;
+
+loser:
+    (void)tls13_AntiReplayReset(NULL, NULL);
+    return SECFailure;
+}
+
+/* This is exposed to tests.  Though it could, this doesn't take the lock on the
+ * basis that those tests use thread confinement. */
+void
+tls13_AntiReplayRollover(PRTime now)
+{
+    ssl_anti_replay.current ^= 1;
+    ssl_anti_replay.nextUpdate = now + ssl_anti_replay.window;
+    sslBloom_Zero(ssl_anti_replay.filters + ssl_anti_replay.current);
+}
+
+static void
+tls13_AntiReplayUpdate()
+{
+    PRTime now;
+
+    PR_ASSERT_CURRENT_THREAD_IN_MONITOR(ssl_anti_replay.lock);
+
+    now = ssl_TimeUsec();
+    if (now < ssl_anti_replay.nextUpdate) {
+        return;
+    }
+
+    tls13_AntiReplayRollover(now);
+}
+
+PRBool
+tls13_InWindow(const sslSocket *ss, const sslSessionID *sid)
+{
+    PRInt32 timeDelta;
+
+    /* Calculate the difference between the client's view of the age of the
+     * ticket (in |ss->xtnData.ticketAge|) and the server's view, which we now
+     * calculate.  The result should be close to zero.  timeDelta is signed to
+     * make the comparisons below easier. */
+    timeDelta = ss->xtnData.ticketAge -
+                ((ssl_TimeUsec() - sid->creationTime) / PR_USEC_PER_MSEC);
+
+    /* Only allow the time delta to be at most half of our window.  This is
+     * symmetrical, though it doesn't need to be; this assumes that clock errors
+     * on server and client will tend to cancel each other out.
+     *
+     * There are two anti-replay filters that roll over each window.  In the
+     * worst case, immediately after a rollover of the filters, we only have a
+     * single window worth of recorded 0-RTT attempts.  Thus, the period in
+     * which we can accept 0-RTT is at most one window wide.  This uses PR_ABS()
+     * and half the window so that the first attempt can be up to half a window
+     * early and then replays will be caught until the attempts are half a
+     * window late.
+     *
+     * For example, a 0-RTT attempt arrives early, but near the end of window 1.
+     * The attempt is then recorded in window 1.  Rollover to window 2 could
+     * occur immediately afterwards.  Window 1 is still checked for new 0-RTT
+     * attempts for the remainder of window 2.  Therefore, attempts to replay
+     * are detected because the value is recorded in window 1.  When rollover
+     * occurs again, window 1 is erased and window 3 instated.  If we allowed an
+     * attempt to be late by more than half a window, then this check would not
+     * prevent the same 0-RTT attempt from being accepted during window 1 and
+     * later window 3.
+     */
+    return PR_ABS(timeDelta) < (ssl_anti_replay.window / 2);
+}
+
+/* Checks for a duplicate in the two filters we have.  Performs maintenance on
+ * the filters as a side-effect. This only detects a probable replay, it's
+ * possible that this will return true when the 0-RTT attempt is not genuinely a
+ * replay.  In that case, we reject 0-RTT unnecessarily, but that's OK because
+ * no client expects 0-RTT to work every time. */
+PRBool
+tls13_IsReplay(const sslSocket *ss, const sslSessionID *sid)
+{
+    PRBool replay;
+    unsigned int size;
+    PRUint8 index;
+    SECStatus rv;
+    static const char *label = "tls13 anti-replay";
+    PRUint8 buf[SSL_MAX_BLOOM_FILTER_SIZE];
+
+    /* If SSL_SetupAntiReplay hasn't been called, then treat all attempts at
+     * 0-RTT as a replay. */
+    if (!ssl_anti_replay.init.initialized) {
+        return PR_TRUE;
+    }
+
+    if (!tls13_InWindow(ss, sid)) {
+        return PR_TRUE;
+    }
+
+    size = ssl_anti_replay.filters[0].k *
+           (ssl_anti_replay.filters[0].bits + 7) / 8;
+    PORT_Assert(size <= SSL_MAX_BLOOM_FILTER_SIZE);
+    rv = tls13_HkdfExpandLabelRaw(ssl_anti_replay.key, ssl_hash_sha256,
+                                  ss->xtnData.pskBinder.data,
+                                  ss->xtnData.pskBinder.len,
+                                  label, strlen(label),
+                                  buf, size);
+    if (rv != SECSuccess) {
+        return PR_TRUE;
+    }
+
+    PZ_EnterMonitor(ssl_anti_replay.lock);
+    tls13_AntiReplayUpdate();
+
+    index = ssl_anti_replay.current;
+    replay = sslBloom_Add(&ssl_anti_replay.filters[index], buf);
+    if (!replay) {
+        replay = sslBloom_Check(&ssl_anti_replay.filters[index ^ 1],
+                                buf);
+    }
+
+    PZ_ExitMonitor(ssl_anti_replay.lock);
+    return replay;
+}