/src/nss/lib/ssl/tls13replay.c

Source
/* -*- 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 "prmon.h"
#include "prtime.h"
#include "secerr.h"
#include "ssl.h"
#include "sslbloom.h"
#include "sslimpl.h"
#include "tls13hkdf.h"
#include "tls13psk.h"

struct SSLAntiReplayContextStr {
    /* The number of outstanding references to this context. */
    PRInt32 refCount;
    /* Used to serialize access. */
    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;
};

void
tls13_ReleaseAntiReplayContext(SSLAntiReplayContext *ctx)
{
    if (!ctx) {
        return;
    }
    if (PR_ATOMIC_DECREMENT(&ctx->refCount) >= 1) {
        return;
    }

    if (ctx->lock) {
        PZ_DestroyMonitor(ctx->lock);
        ctx->lock = NULL;
    }
    PK11_FreeSymKey(ctx->key);
    ctx->key = NULL;
    sslBloom_Destroy(&ctx->filters[0]);
    sslBloom_Destroy(&ctx->filters[1]);
    PORT_Free(ctx);
}

/* Clear the current state and free any resources we allocated. */
SECStatus
SSLExp_ReleaseAntiReplayContext(SSLAntiReplayContext *ctx)
{
    tls13_ReleaseAntiReplayContext(ctx);
    return SECSuccess;
}

SSLAntiReplayContext *
tls13_RefAntiReplayContext(SSLAntiReplayContext *ctx)
{
    PORT_Assert(ctx);
    PR_ATOMIC_INCREMENT(&ctx->refCount);
    return ctx;
}

static SECStatus
tls13_AntiReplayKeyGen(SSLAntiReplayContext *ctx)
{
    PK11SlotInfo *slot;

    PORT_Assert(ctx);

    slot = PK11_GetBestSlot(CKM_HKDF_DERIVE, NULL);
    if (!slot) {
        PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);
        return SECFailure;
    }

    ctx->key = PK11_KeyGen(slot, CKM_HKDF_KEY_GEN, NULL, 32, NULL);
    if (!ctx->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 context 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.
 */
SECStatus
SSLExp_CreateAntiReplayContext(PRTime now, PRTime window, unsigned int k,
                               unsigned int bits, SSLAntiReplayContext **pctx)
{
    SECStatus rv;

    if (window <= 0 || k == 0 || bits == 0 || pctx == NULL) {
        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;
    }

    SSLAntiReplayContext *ctx = PORT_ZNew(SSLAntiReplayContext);
    if (!ctx) {
        return SECFailure; /* Code already set. */
    }

    ctx->refCount = 1;
    ctx->lock = PZ_NewMonitor(nssILockSSL);
    if (!ctx->lock) {
        goto loser; /* Code already set. */
    }

    rv = tls13_AntiReplayKeyGen(ctx);
    if (rv != SECSuccess) {
        goto loser; /* Code already set. */
    }

    rv = sslBloom_Init(&ctx->filters[0], k, bits);
    if (rv != SECSuccess) {
        goto loser; /* Code already set. */
    }
    rv = sslBloom_Init(&ctx->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(&ctx->filters[1]);

    ctx->current = 0;
    ctx->nextUpdate = now + window;
    ctx->window = window;
    *pctx = ctx;
    return SECSuccess;

loser:
    tls13_ReleaseAntiReplayContext(ctx);
    return SECFailure;
}

SECStatus
SSLExp_SetAntiReplayContext(PRFileDesc *fd, SSLAntiReplayContext *ctx)
{
    sslSocket *ss = ssl_FindSocket(fd);
    if (!ss) {
        return SECFailure; /* Code already set. */
    }
    tls13_ReleaseAntiReplayContext(ss->antiReplay);
    if (ctx != NULL) {
        ss->antiReplay = tls13_RefAntiReplayContext(ctx);
    } else {
        ss->antiReplay = NULL;
    }
    return SECSuccess;
}

static void
tls13_AntiReplayUpdate(SSLAntiReplayContext *ctx, PRTime now)
{
    PR_ASSERT_CURRENT_THREAD_IN_MONITOR(ctx->lock);
    if (now >= ctx->nextUpdate) {
        ctx->current ^= 1;
        ctx->nextUpdate = now + ctx->window;
        sslBloom_Zero(ctx->filters + ctx->current);
    }
}

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_Time(ss) - 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.
     */
    PRInt32 allowance = ss->antiReplay->window / (PR_USEC_PER_MSEC * 2);
    SSL_TRC(10, ("%d: TLS13[%d]: replay check time delta=%d, allow=%d",
                 SSL_GETPID(), ss->fd, timeDelta, allowance));
    return PR_ABS(timeDelta) < allowance;
}

/* 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 = "anti-replay";
    PRUint8 buf[SSL_MAX_BLOOM_FILTER_SIZE];
    SSLAntiReplayContext *ctx = ss->antiReplay;

    /* If SSL_SetAntiReplayContext hasn't been called with a valid context, then
     * treat all attempts at 0-RTT as a replay. */
    if (ctx == NULL) {
        return PR_TRUE;
    }

    if (!sid) {
        PORT_Assert(ss->xtnData.selectedPsk->type == ssl_psk_external);
    } else if (!tls13_InWindow(ss, sid)) {
        return PR_TRUE;
    }

    size = ctx->filters[0].k * (ctx->filters[0].bits + 7) / 8;
    PORT_Assert(size <= SSL_MAX_BLOOM_FILTER_SIZE);
    rv = tls13_HkdfExpandLabelRaw(ctx->key, ssl_hash_sha256,
                                  ss->xtnData.pskBinder.data,
                                  ss->xtnData.pskBinder.len,
                                  label, strlen(label),
                                  ss->protocolVariant, buf, size);
    if (rv != SECSuccess) {
        return PR_TRUE;
    }

    PZ_EnterMonitor(ctx->lock);
    tls13_AntiReplayUpdate(ctx, ssl_Time(ss));

    index = ctx->current;
    replay = sslBloom_Add(&ctx->filters[index], buf);
    SSL_TRC(10, ("%d: TLS13[%d]: replay check current window: %s",
                 SSL_GETPID(), ss->fd, replay ? "replay" : "ok"));
    if (!replay) {
        replay = sslBloom_Check(&ctx->filters[index ^ 1], buf);
        SSL_TRC(10, ("%d: TLS13[%d]: replay check previous window: %s",
                     SSL_GETPID(), ss->fd, replay ? "replay" : "ok"));
    }

    PZ_ExitMonitor(ctx->lock);
    return replay;
}

Coverage Report

Created: 2025-12-20 07:02

Line	Count	Source
1		/* -- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -- */
2		/*
3		* Anti-replay measures for TLS 1.3.
4		*
5		* This Source Code Form is subject to the terms of the Mozilla Public
6		* License, v. 2.0. If a copy of the MPL was not distributed with this
7		* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
8
9		#include "nss.h" /* for NSS_RegisterShutdown */
10		#include "nssilock.h" /* for PZMonitor */
11		#include "pk11pub.h"
12		#include "prmon.h"
13		#include "prtime.h"
14		#include "secerr.h"
15		#include "ssl.h"
16		#include "sslbloom.h"
17		#include "sslimpl.h"
18		#include "tls13hkdf.h"
19		#include "tls13psk.h"
20
21		struct SSLAntiReplayContextStr {
22		/* The number of outstanding references to this context. */
23		PRInt32 refCount;
24		/* Used to serialize access. */
25		PZMonitor *lock;
26		/* The filters, use of which alternates. */
27		sslBloomFilter filters[2];
28		/* Which of the two filters is active (0 or 1). */
29		PRUint8 current;
30		/* The time that we will next update. */
31		PRTime nextUpdate;
32		/* The width of the window; i.e., the period of updates. */
33		PRTime window;
34		/* This key ensures that the bloom filter index is unpredictable. */
35		PK11SymKey *key;
36		};
37
38		void
39		tls13_ReleaseAntiReplayContext(SSLAntiReplayContext *ctx)
40	66.4k	{
41	66.4k	if (!ctx) {
42	66.4k	return;
43	66.4k	}
44	0	if (PR_ATOMIC_DECREMENT(&ctx->refCount) >= 1) {
45	0	return;
46	0	}
47
48	0	if (ctx->lock) {
49	0	PZ_DestroyMonitor(ctx->lock);
50	0	ctx->lock = NULL;
51	0	}
52	0	PK11_FreeSymKey(ctx->key);
53	0	ctx->key = NULL;
54	0	sslBloom_Destroy(&ctx->filters[0]);
55	0	sslBloom_Destroy(&ctx->filters[1]);
56	0	PORT_Free(ctx);
57	0	}
58
59		/* Clear the current state and free any resources we allocated. */
60		SECStatus
61		SSLExp_ReleaseAntiReplayContext(SSLAntiReplayContext *ctx)
62	0	{
63	0	tls13_ReleaseAntiReplayContext(ctx);
64	0	return SECSuccess;
65	0	}
66
67		SSLAntiReplayContext *
68		tls13_RefAntiReplayContext(SSLAntiReplayContext *ctx)
69	0	{
70	0	PORT_Assert(ctx);
71	0	PR_ATOMIC_INCREMENT(&ctx->refCount);
72	0	return ctx;
73	0	}
74
75		static SECStatus
76		tls13_AntiReplayKeyGen(SSLAntiReplayContext *ctx)
77	0	{
78	0	PK11SlotInfo *slot;
79
80	0	PORT_Assert(ctx);
81
82	0	slot = PK11_GetBestSlot(CKM_HKDF_DERIVE, NULL);
83	0	if (!slot) {
84	0	PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);
85	0	return SECFailure;
86	0	}
87
88	0	ctx->key = PK11_KeyGen(slot, CKM_HKDF_KEY_GEN, NULL, 32, NULL);
89	0	if (!ctx->key) {
90	0	goto loser;
91	0	}
92
93	0	PK11_FreeSlot(slot);
94	0	return SECSuccess;
95
96	0	loser:
97	0	PK11_FreeSlot(slot);
98	0	return SECFailure;
99	0	}
100
101		/* Set a limit on the combination of number of hashes and bits in each hash. */
102	0	#define SSL_MAX_BLOOM_FILTER_SIZE 64
103
104		/*
105		* The context created by this function can be called concurrently on multiple
106		* threads if the server is multi-threaded. A monitor is used to ensure that
107		* only one thread can access the structures that change over time, but no such
108		* guarantee is provided for configuration data.
109		*/
110		SECStatus
111		SSLExp_CreateAntiReplayContext(PRTime now, PRTime window, unsigned int k,
112		unsigned int bits, SSLAntiReplayContext **pctx)
113	0	{
114	0	SECStatus rv;
115
116	0	if (window <= 0 \|\| k == 0 \|\| bits == 0 \|\| pctx == NULL) {
117	0	PORT_SetError(SEC_ERROR_INVALID_ARGS);
118	0	return SECFailure;
119	0	}
120	0	if ((k * (bits + 7) / 8) > SSL_MAX_BLOOM_FILTER_SIZE) {
121	0	PORT_SetError(SEC_ERROR_INVALID_ARGS);
122	0	return SECFailure;
123	0	}
124
125	0	SSLAntiReplayContext *ctx = PORT_ZNew(SSLAntiReplayContext);
126	0	if (!ctx) {
127	0	return SECFailure; /* Code already set. */
128	0	}
129
130	0	ctx->refCount = 1;
131	0	ctx->lock = PZ_NewMonitor(nssILockSSL);
132	0	if (!ctx->lock) {
133	0	goto loser; /* Code already set. */
134	0	}
135
136	0	rv = tls13_AntiReplayKeyGen(ctx);
137	0	if (rv != SECSuccess) {
138	0	goto loser; /* Code already set. */
139	0	}
140
141	0	rv = sslBloom_Init(&ctx->filters[0], k, bits);
142	0	if (rv != SECSuccess) {
143	0	goto loser; /* Code already set. */
144	0	}
145	0	rv = sslBloom_Init(&ctx->filters[1], k, bits);
146	0	if (rv != SECSuccess) {
147	0	goto loser; /* Code already set. */
148	0	}
149		/* When starting out, ensure that 0-RTT is not accepted until the window is
150		* updated. A ClientHello might have been accepted prior to a restart. */
151	0	sslBloom_Fill(&ctx->filters[1]);
152
153	0	ctx->current = 0;
154	0	ctx->nextUpdate = now + window;
155	0	ctx->window = window;
156	0	*pctx = ctx;
157	0	return SECSuccess;
158
159	0	loser:
160	0	tls13_ReleaseAntiReplayContext(ctx);
161	0	return SECFailure;
162	0	}
163
164		SECStatus
165		SSLExp_SetAntiReplayContext(PRFileDesc fd, SSLAntiReplayContext ctx)
166	0	{
167	0	sslSocket *ss = ssl_FindSocket(fd);
168	0	if (!ss) {
169	0	return SECFailure; /* Code already set. */
170	0	}
171	0	tls13_ReleaseAntiReplayContext(ss->antiReplay);
172	0	if (ctx != NULL) {
173	0	ss->antiReplay = tls13_RefAntiReplayContext(ctx);
174	0	} else {
175	0	ss->antiReplay = NULL;
176	0	}
177	0	return SECSuccess;
178	0	}
179
180		static void
181		tls13_AntiReplayUpdate(SSLAntiReplayContext *ctx, PRTime now)
182	0	{
183	0	PR_ASSERT_CURRENT_THREAD_IN_MONITOR(ctx->lock);
184	0	if (now >= ctx->nextUpdate) {
185	0	ctx->current ^= 1;
186	0	ctx->nextUpdate = now + ctx->window;
187	0	sslBloom_Zero(ctx->filters + ctx->current);
188	0	}
189	0	}
190
191		PRBool
192		tls13_InWindow(const sslSocket ss, const sslSessionID sid)
193	0	{
194	0	PRInt32 timeDelta;
195
196		/* Calculate the difference between the client's view of the age of the
197		* ticket (in \|ss->xtnData.ticketAge\|) and the server's view, which we now
198		* calculate. The result should be close to zero. timeDelta is signed to
199		* make the comparisons below easier. */
200	0	timeDelta = ss->xtnData.ticketAge -
201	0	((ssl_Time(ss) - sid->creationTime) / PR_USEC_PER_MSEC);
202
203		/* Only allow the time delta to be at most half of our window. This is
204		* symmetrical, though it doesn't need to be; this assumes that clock errors
205		* on server and client will tend to cancel each other out.
206		*
207		* There are two anti-replay filters that roll over each window. In the
208		* worst case, immediately after a rollover of the filters, we only have a
209		* single window worth of recorded 0-RTT attempts. Thus, the period in
210		* which we can accept 0-RTT is at most one window wide. This uses PR_ABS()
211		* and half the window so that the first attempt can be up to half a window
212		* early and then replays will be caught until the attempts are half a
213		* window late.
214		*
215		* For example, a 0-RTT attempt arrives early, but near the end of window 1.
216		* The attempt is then recorded in window 1. Rollover to window 2 could
217		* occur immediately afterwards. Window 1 is still checked for new 0-RTT
218		* attempts for the remainder of window 2. Therefore, attempts to replay
219		* are detected because the value is recorded in window 1. When rollover
220		* occurs again, window 1 is erased and window 3 instated. If we allowed an
221		* attempt to be late by more than half a window, then this check would not
222		* prevent the same 0-RTT attempt from being accepted during window 1 and
223		* later window 3.
224		*/
225	0	PRInt32 allowance = ss->antiReplay->window / (PR_USEC_PER_MSEC * 2);
226	0	SSL_TRC(10, ("%d: TLS13[%d]: replay check time delta=%d, allow=%d",
227	0	SSL_GETPID(), ss->fd, timeDelta, allowance));
228	0	return PR_ABS(timeDelta) < allowance;
229	0	}
230
231		/* Checks for a duplicate in the two filters we have. Performs maintenance on
232		* the filters as a side-effect. This only detects a probable replay, it's
233		* possible that this will return true when the 0-RTT attempt is not genuinely a
234		* replay. In that case, we reject 0-RTT unnecessarily, but that's OK because
235		* no client expects 0-RTT to work every time. */
236		PRBool
237		tls13_IsReplay(const sslSocket ss, const sslSessionID sid)
238	0	{
239	0	PRBool replay;
240	0	unsigned int size;
241	0	PRUint8 index;
242	0	SECStatus rv;
243	0	static const char *label = "anti-replay";
244	0	PRUint8 buf[SSL_MAX_BLOOM_FILTER_SIZE];
245	0	SSLAntiReplayContext *ctx = ss->antiReplay;
246
247		/* If SSL_SetAntiReplayContext hasn't been called with a valid context, then
248		* treat all attempts at 0-RTT as a replay. */
249	0	if (ctx == NULL) {
250	0	return PR_TRUE;
251	0	}
252
253	0	if (!sid) {
254	0	PORT_Assert(ss->xtnData.selectedPsk->type == ssl_psk_external);
255	0	} else if (!tls13_InWindow(ss, sid)) {
256	0	return PR_TRUE;
257	0	}
258
259	0	size = ctx->filters[0].k * (ctx->filters[0].bits + 7) / 8;
260	0	PORT_Assert(size <= SSL_MAX_BLOOM_FILTER_SIZE);
261	0	rv = tls13_HkdfExpandLabelRaw(ctx->key, ssl_hash_sha256,
262	0	ss->xtnData.pskBinder.data,
263	0	ss->xtnData.pskBinder.len,
264	0	label, strlen(label),
265	0	ss->protocolVariant, buf, size);
266	0	if (rv != SECSuccess) {
267	0	return PR_TRUE;
268	0	}
269
270	0	PZ_EnterMonitor(ctx->lock);
271	0	tls13_AntiReplayUpdate(ctx, ssl_Time(ss));
272
273	0	index = ctx->current;
274	0	replay = sslBloom_Add(&ctx->filters[index], buf);
275	0	SSL_TRC(10, ("%d: TLS13[%d]: replay check current window: %s",
276	0	SSL_GETPID(), ss->fd, replay ? "replay" : "ok"));
277	0	if (!replay) {
278	0	replay = sslBloom_Check(&ctx->filters[index ^ 1], buf);
279	0	SSL_TRC(10, ("%d: TLS13[%d]: replay check previous window: %s",
280	0	SSL_GETPID(), ss->fd, replay ? "replay" : "ok"));
281	0	}
282
283	0	PZ_ExitMonitor(ctx->lock);
284	0	return replay;
285	0	}