ssl/sslgathr.c - chromium/src/net/third_party/nss - Git at Google

 /*
  * Gather (Read) entire SSL2 records from socket into buffer.
  *
  * 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 "cert.h"
 #include "ssl.h"
 #include "sslimpl.h"
 #include "sslproto.h"

 /* Forward static declarations */
 static SECStatus ssl2_HandleV3HandshakeRecord(sslSocket *ss);

 /*
 ** Gather a single record of data from the receiving stream. This code
 ** first gathers the header (2 or 3 bytes long depending on the value of
 ** the most significant bit in the first byte) then gathers up the data
 ** for the record into gs->buf. This code handles non-blocking I/O
 ** and is to be called multiple times until ss->sec.recordLen != 0.
 ** This function decrypts the gathered record in place, in gs_buf.
  *
  * Caller must hold RecvBufLock.
  *
  * Returns +1 when it has gathered a complete SSLV2 record.
  * Returns  0 if it hits EOF.
  * Returns -1 (SECFailure)    on any error
  * Returns -2 (SECWouldBlock) when it gathers an SSL v3 client hello header.
 **
 ** The SSL2 Gather State machine has 4 states:
 ** GS_INIT   - Done reading in previous record.  Haven't begun to read in
 **             next record.  When ssl2_GatherData is called with the machine
 **             in this state, the machine will attempt to read the first 3
 **             bytes of the SSL2 record header, and will advance the state
 **             to GS_HEADER.
 **
 ** GS_HEADER - The machine is in this state while waiting for the completion
 **             of the first 3 bytes of the SSL2 record.  When complete, the
 **             machine will compute the remaining unread length of this record
 **             and will initiate a read of that many bytes.  The machine will
 **             advance to one of two states, depending on whether the record
 **             is encrypted (GS_MAC), or unencrypted (GS_DATA).
 **
 ** GS_MAC    - The machine is in this state while waiting for the remainder
 **             of the SSL2 record to be read in.  When the read is completed,
 **             the machine checks the record for valid length, decrypts it,
 **             and checks and discards the MAC, then advances to GS_INIT.
 **
 ** GS_DATA   - The machine is in this state while waiting for the remainder
 **             of the unencrypted SSL2 record to be read in.  Upon completion,
 **             the machine advances to the GS_INIT state and returns the data.
 */
 int
 ssl2_GatherData(sslSocket *ss, sslGather *gs, int flags)
 {
     unsigned char *bp;
     unsigned char *pBuf;
     int nb, err, rv;

     PORT_Assert(ss->opt.noLocks || ssl_HaveRecvBufLock(ss));

     if (gs->state == GS_INIT) {
         /* Initialize gathering engine */
         gs->state = GS_HEADER;
         gs->remainder = 3;
         gs->count = 3;
         gs->offset = 0;
         gs->recordLen = 0;
         gs->recordPadding = 0;
         gs->hdr[2] = 0;

         gs->writeOffset = 0;
         gs->readOffset = 0;
     }
     if (gs->encrypted) {
         PORT_Assert(ss->sec.hash != 0);
     }

     pBuf = gs->buf.buf;
     for (;;) {
         SSL_TRC(30, ("%d: SSL[%d]: gather state %d (need %d more)",
                      SSL_GETPID(), ss->fd, gs->state, gs->remainder));
         bp = ((gs->state != GS_HEADER) ? pBuf : gs->hdr) + gs->offset;
         nb = ssl_DefRecv(ss, bp, gs->remainder, flags);
         if (nb > 0) {
             PRINT_BUF(60, (ss, "raw gather data:", bp, nb));
         }
         if (nb == 0) {
             /* EOF */
             SSL_TRC(30, ("%d: SSL[%d]: EOF", SSL_GETPID(), ss->fd));
             rv = 0;
             break;
         }
         if (nb < 0) {
             SSL_DBG(("%d: SSL[%d]: recv error %d", SSL_GETPID(), ss->fd,
                      PR_GetError()));
             rv = SECFailure;
             break;
         }

         gs->offset += nb;
         gs->remainder -= nb;

         if (gs->remainder > 0) {
             continue;
         }

         /* Probably finished this piece */
         switch (gs->state) {
             case GS_HEADER:
                 if (!SSL3_ALL_VERSIONS_DISABLED(&ss->vrange) && !ss->firstHsDone) {

                     PORT_Assert(ss->opt.noLocks || ssl_Have1stHandshakeLock(ss));

                     /* If this looks like an SSL3 handshake record,
                     ** and we're expecting an SSL2 Hello message from our peer,
                     ** handle it here.
                     */
                     if (gs->hdr[0] == content_handshake) {
                         if ((ss->nextHandshake == ssl2_HandleClientHelloMessage) ||
                             (ss->nextHandshake == ssl2_HandleServerHelloMessage)) {
                             rv = ssl2_HandleV3HandshakeRecord(ss);
                             if (rv == SECFailure) {
                                 return SECFailure;
                             }
                         }
                         /* XXX_1    The call stack to here is:
                          * ssl_Do1stHandshake -> ssl_GatherRecord1stHandshake ->
                          *          ssl2_GatherRecord -> here.
                          * We want to return all the way out to ssl_Do1stHandshake,
                          * and have it call ssl_GatherRecord1stHandshake again.
                          * ssl_GatherRecord1stHandshake will call
                          * ssl3_GatherCompleteHandshake when it is called again.
                          *
                          * Returning SECWouldBlock here causes
                          * ssl_GatherRecord1stHandshake to return without clearing
                          * ss->handshake, ensuring that ssl_Do1stHandshake will
                          * call it again immediately.
                          *
                          * If we return 1 here, ssl_GatherRecord1stHandshake will
                          * clear ss->handshake before returning, and thus will not
                          * be called again by ssl_Do1stHandshake.
                          */
                         return SECWouldBlock;
                     } else if (gs->hdr[0] == content_alert) {
                         if (ss->nextHandshake == ssl2_HandleServerHelloMessage) {
                             /* XXX This is a hack.  We're assuming that any failure
                              * XXX on the client hello is a failure to match
                              * XXX ciphers.
                              */
                             PORT_SetError(SSL_ERROR_NO_CYPHER_OVERLAP);
                             return SECFailure;
                         }
                     }
                 }

                 /* we've got the first 3 bytes.  The header may be two or three. */
                 if (gs->hdr[0] & 0x80) {
                     /* This record has a 2-byte header, and no padding */
                     gs->count = ((gs->hdr[0] & 0x7f) << 8) | gs->hdr[1];
                     gs->recordPadding = 0;
                 } else {
                     /* This record has a 3-byte header that is all read in now. */
                     gs->count = ((gs->hdr[0] & 0x3f) << 8) | gs->hdr[1];
                     /*  is_escape =  (gs->hdr[0] & 0x40) != 0; */
                     gs->recordPadding = gs->hdr[2];
                 }
                 if (!gs->count) {
                     PORT_SetError(SSL_ERROR_RX_RECORD_TOO_LONG);
                     goto cleanup;
                 }

                 if (gs->count > gs->buf.space) {
                     err = sslBuffer_Grow(&gs->buf, gs->count);
                     if (err) {
                         return err;
                     }
                     pBuf = gs->buf.buf;
                 }

                 if (gs->hdr[0] & 0x80) {
                     /* we've already read in the first byte of the body.
                     ** Put it into the buffer.
                     */
                     pBuf[0] = gs->hdr[2];
                     gs->offset = 1;
                     gs->remainder = gs->count - 1;
                 } else {
                     gs->offset = 0;
                     gs->remainder = gs->count;
                 }

                 if (gs->encrypted) {
                     gs->state = GS_MAC;
                     gs->recordLen = gs->count - gs->recordPadding -
                                     ss->sec.hash->length;
                 } else {
                     gs->state = GS_DATA;
                     gs->recordLen = gs->count;
                 }

                 break;

             case GS_MAC:
                 /* Have read in entire rest of the ciphertext.
                 ** Check for valid length.
                 ** Decrypt it.
                 ** Check the MAC.
                 */
                 PORT_Assert(gs->encrypted);

                 {
                     unsigned int macLen;
                     int nout;
                     unsigned char mac[SSL_MAX_MAC_BYTES];

                     ssl_GetSpecReadLock(ss); /**********************************/

                     /* If this is a stream cipher, blockSize will be 1,
                      * and this test will always be false.
                      * If this is a block cipher, this will detect records
                      * that are not a multiple of the blocksize in length.
                      */
                     if (gs->count & (ss->sec.blockSize - 1)) {
                         /* This is an error. Sender is misbehaving */
                         SSL_DBG(("%d: SSL[%d]: sender, count=%d blockSize=%d",
                                  SSL_GETPID(), ss->fd, gs->count,
                                  ss->sec.blockSize));
                         PORT_SetError(SSL_ERROR_BAD_BLOCK_PADDING);
                         rv = SECFailure;
                         goto spec_locked_done;
                     }
                     PORT_Assert(gs->count == gs->offset);

                     if (gs->offset == 0) {
                         rv = 0; /* means EOF. */
                         goto spec_locked_done;
                     }

                     /* Decrypt the portion of data that we just received.
                     ** Decrypt it in place.
                     */
                     rv = (*ss->sec.dec)(ss->sec.readcx, pBuf, &nout, gs->offset,
                                         pBuf, gs->offset);
                     if (rv != SECSuccess) {
                         goto spec_locked_done;
                     }

                     /* Have read in all the MAC portion of record
                     **
                     ** Prepare MAC by resetting it and feeding it the shared secret
                     */
                     macLen = ss->sec.hash->length;
                     if (gs->offset >= macLen) {
                         PRUint32 sequenceNumber = ss->sec.rcvSequence++;
                         unsigned char seq[4];

                         seq[0] = (unsigned char)(sequenceNumber >> 24);
                         seq[1] = (unsigned char)(sequenceNumber >> 16);
                         seq[2] = (unsigned char)(sequenceNumber >> 8);
                         seq[3] = (unsigned char)(sequenceNumber);

                         (*ss->sec.hash->begin)(ss->sec.hashcx);
                         (*ss->sec.hash->update)(ss->sec.hashcx, ss->sec.rcvSecret.data,
                                                 ss->sec.rcvSecret.len);
                         (*ss->sec.hash->update)(ss->sec.hashcx, pBuf + macLen,
                                                 gs->offset - macLen);
                         (*ss->sec.hash->update)(ss->sec.hashcx, seq, 4);
                         (*ss->sec.hash->end)(ss->sec.hashcx, mac, &macLen, macLen);

                         PORT_Assert(macLen == ss->sec.hash->length);

                         ssl_ReleaseSpecReadLock(ss); /******************************/

                         if (NSS_SecureMemcmp(mac, pBuf, macLen) != 0) {
                             /* MAC's didn't match... */
                             SSL_DBG(("%d: SSL[%d]: mac check failed, seq=%d",
                                      SSL_GETPID(), ss->fd, ss->sec.rcvSequence));
                             PRINT_BUF(1, (ss, "computed mac:", mac, macLen));
                             PRINT_BUF(1, (ss, "received mac:", pBuf, macLen));
                             PORT_SetError(SSL_ERROR_BAD_MAC_READ);
                             rv = SECFailure;
                             goto cleanup;
                         }
                     } else {
                         ssl_ReleaseSpecReadLock(ss); /******************************/
                     }

                     if (gs->recordPadding + macLen <= gs->offset) {
                         gs->recordOffset = macLen;
                         gs->readOffset = macLen;
                         gs->writeOffset = gs->offset - gs->recordPadding;
                         rv = 1;
                     } else {
                         PORT_SetError(SSL_ERROR_BAD_BLOCK_PADDING);
                     cleanup:
                         /* nothing in the buffer any more. */
                         gs->recordOffset = 0;
                         gs->readOffset = 0;
                         gs->writeOffset = 0;
                         rv = SECFailure;
                     }

                     gs->recordLen = gs->writeOffset - gs->readOffset;
                     gs->recordPadding = 0; /* forget we did any padding. */
                     gs->state = GS_INIT;

                     if (rv > 0) {
                         PRINT_BUF(50, (ss, "recv clear record:",
                                        pBuf + gs->recordOffset, gs->recordLen));
                     }
                     return rv;

                 spec_locked_done:
                     ssl_ReleaseSpecReadLock(ss);
                     return rv;
                 }

             case GS_DATA:
                 /* Have read in all the DATA portion of record */

                 gs->recordOffset = 0;
                 gs->readOffset = 0;
                 gs->writeOffset = gs->offset;
                 PORT_Assert(gs->recordLen == gs->writeOffset - gs->readOffset);
                 gs->recordLen = gs->offset;
                 gs->recordPadding = 0;
                 gs->state = GS_INIT;

                 ++ss->sec.rcvSequence;

                 PRINT_BUF(50, (ss, "recv clear record:",
                                pBuf + gs->recordOffset, gs->recordLen));
                 return 1;

         } /* end switch gs->state */
     }     /* end gather loop. */
     return rv;
 }

 /*
 ** Gather a single record of data from the receiving stream. This code
 ** first gathers the header (2 or 3 bytes long depending on the value of
 ** the most significant bit in the first byte) then gathers up the data
 ** for the record into the readBuf. This code handles non-blocking I/O
 ** and is to be called multiple times until ss->sec.recordLen != 0.
  *
  * Returns +1 when it has gathered a complete SSLV2 record.
  * Returns  0 if it hits EOF.
  * Returns -1 (SECFailure)    on any error
  * Returns -2 (SECWouldBlock)
  *
  * Called by ssl_GatherRecord1stHandshake in sslcon.c,
  * and by DoRecv in sslsecur.c
  * Caller must hold RecvBufLock.
  */
 int
 ssl2_GatherRecord(sslSocket *ss, int flags)
 {
     return ssl2_GatherData(ss, &ss->gs, flags);
 }

 /* Caller should hold RecvBufLock. */
 SECStatus
 ssl_InitGather(sslGather *gs)
 {
     SECStatus status;

     gs->state = GS_INIT;
     gs->writeOffset = 0;
     gs->readOffset = 0;
     gs->dtlsPacketOffset = 0;
     gs->dtlsPacket.len = 0;
     status = sslBuffer_Grow(&gs->buf, 4096);
     return status;
 }

 /* Caller must hold RecvBufLock. */
 void
 ssl_DestroyGather(sslGather *gs)
 {
     if (gs) { /* the PORT_*Free functions check for NULL pointers. */
         PORT_ZFree(gs->buf.buf, gs->buf.space);
         PORT_Free(gs->inbuf.buf);
         PORT_Free(gs->dtlsPacket.buf);
     }
 }

 /* Caller must hold RecvBufLock. */
 static SECStatus
 ssl2_HandleV3HandshakeRecord(sslSocket *ss)
 {
     SECStatus rv;

     PORT_Assert(ss->opt.noLocks || ssl_HaveRecvBufLock(ss));
     PORT_Assert(ss->opt.noLocks || ssl_Have1stHandshakeLock(ss));

     /* We've read in 3 bytes, there are 2 more to go in an ssl3 header. */
     ss->gs.remainder = 2;
     ss->gs.count = 0;

     /* Clearing these handshake pointers ensures that
      * ssl_Do1stHandshake won't call ssl2_HandleMessage when we return.
      */
     ss->nextHandshake = 0;
     ss->securityHandshake = 0;

     /* Setting ss->version to an SSL 3.x value will cause
     ** ssl_GatherRecord1stHandshake to invoke ssl3_GatherCompleteHandshake()
     ** the next time it is called.
     **/
     rv = ssl3_NegotiateVersion(ss, SSL_LIBRARY_VERSION_MAX_SUPPORTED,
                                PR_TRUE);
     if (rv != SECSuccess) {
         return rv;
     }

     ss->sec.send = ssl3_SendApplicationData;

     return SECSuccess;
 }
	/*
	* Gather (Read) entire SSL2 records from socket into buffer.
	*
	* 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 "cert.h"
	#include "ssl.h"
	#include "sslimpl.h"
	#include "sslproto.h"

	/* Forward static declarations */
	static SECStatus ssl2_HandleV3HandshakeRecord(sslSocket *ss);

	/*
	** Gather a single record of data from the receiving stream. This code
	** first gathers the header (2 or 3 bytes long depending on the value of
	** the most significant bit in the first byte) then gathers up the data
	** for the record into gs->buf. This code handles non-blocking I/O
	** and is to be called multiple times until ss->sec.recordLen != 0.
	** This function decrypts the gathered record in place, in gs_buf.
	*
	* Caller must hold RecvBufLock.
	*
	* Returns +1 when it has gathered a complete SSLV2 record.
	* Returns 0 if it hits EOF.
	* Returns -1 (SECFailure) on any error
	* Returns -2 (SECWouldBlock) when it gathers an SSL v3 client hello header.
	**
	** The SSL2 Gather State machine has 4 states:
	** GS_INIT - Done reading in previous record. Haven't begun to read in
	** next record. When ssl2_GatherData is called with the machine
	** in this state, the machine will attempt to read the first 3
	** bytes of the SSL2 record header, and will advance the state
	** to GS_HEADER.
	**
	** GS_HEADER - The machine is in this state while waiting for the completion
	** of the first 3 bytes of the SSL2 record. When complete, the
	** machine will compute the remaining unread length of this record
	** and will initiate a read of that many bytes. The machine will
	** advance to one of two states, depending on whether the record
	** is encrypted (GS_MAC), or unencrypted (GS_DATA).
	**
	** GS_MAC - The machine is in this state while waiting for the remainder
	** of the SSL2 record to be read in. When the read is completed,
	** the machine checks the record for valid length, decrypts it,
	** and checks and discards the MAC, then advances to GS_INIT.
	**
	** GS_DATA - The machine is in this state while waiting for the remainder
	** of the unencrypted SSL2 record to be read in. Upon completion,
	** the machine advances to the GS_INIT state and returns the data.
	*/
	int
	ssl2_GatherData(sslSocket ss, sslGather gs, int flags)
	{
	unsigned char *bp;
	unsigned char *pBuf;
	int nb, err, rv;

	PORT_Assert(ss->opt.noLocks \|\| ssl_HaveRecvBufLock(ss));

	if (gs->state == GS_INIT) {
	/* Initialize gathering engine */
	gs->state = GS_HEADER;
	gs->remainder = 3;
	gs->count = 3;
	gs->offset = 0;
	gs->recordLen = 0;
	gs->recordPadding = 0;
	gs->hdr[2] = 0;

	gs->writeOffset = 0;
	gs->readOffset = 0;
	}
	if (gs->encrypted) {
	PORT_Assert(ss->sec.hash != 0);
	}

	pBuf = gs->buf.buf;
	for (;;) {
	SSL_TRC(30, ("%d: SSL[%d]: gather state %d (need %d more)",
	SSL_GETPID(), ss->fd, gs->state, gs->remainder));
	bp = ((gs->state != GS_HEADER) ? pBuf : gs->hdr) + gs->offset;
	nb = ssl_DefRecv(ss, bp, gs->remainder, flags);
	if (nb > 0) {
	PRINT_BUF(60, (ss, "raw gather data:", bp, nb));
	}
	if (nb == 0) {
	/* EOF */
	SSL_TRC(30, ("%d: SSL[%d]: EOF", SSL_GETPID(), ss->fd));
	rv = 0;
	break;
	}
	if (nb < 0) {
	SSL_DBG(("%d: SSL[%d]: recv error %d", SSL_GETPID(), ss->fd,
	PR_GetError()));
	rv = SECFailure;
	break;
	}

	gs->offset += nb;
	gs->remainder -= nb;

	if (gs->remainder > 0) {
	continue;
	}

	/* Probably finished this piece */
	switch (gs->state) {
	case GS_HEADER:
	if (!SSL3_ALL_VERSIONS_DISABLED(&ss->vrange) && !ss->firstHsDone) {

	PORT_Assert(ss->opt.noLocks \|\| ssl_Have1stHandshakeLock(ss));

	/* If this looks like an SSL3 handshake record,
	** and we're expecting an SSL2 Hello message from our peer,
	** handle it here.
	*/
	if (gs->hdr[0] == content_handshake) {
	if ((ss->nextHandshake == ssl2_HandleClientHelloMessage) \|\|
	(ss->nextHandshake == ssl2_HandleServerHelloMessage)) {
	rv = ssl2_HandleV3HandshakeRecord(ss);
	if (rv == SECFailure) {
	return SECFailure;
	}
	}
	/* XXX_1 The call stack to here is:
	* ssl_Do1stHandshake -> ssl_GatherRecord1stHandshake ->
	* ssl2_GatherRecord -> here.
	* We want to return all the way out to ssl_Do1stHandshake,
	* and have it call ssl_GatherRecord1stHandshake again.
	* ssl_GatherRecord1stHandshake will call
	* ssl3_GatherCompleteHandshake when it is called again.
	*
	* Returning SECWouldBlock here causes
	* ssl_GatherRecord1stHandshake to return without clearing
	* ss->handshake, ensuring that ssl_Do1stHandshake will
	* call it again immediately.
	*
	* If we return 1 here, ssl_GatherRecord1stHandshake will
	* clear ss->handshake before returning, and thus will not
	* be called again by ssl_Do1stHandshake.
	*/
	return SECWouldBlock;
	} else if (gs->hdr[0] == content_alert) {
	if (ss->nextHandshake == ssl2_HandleServerHelloMessage) {
	/* XXX This is a hack. We're assuming that any failure
	* XXX on the client hello is a failure to match
	* XXX ciphers.
	*/
	PORT_SetError(SSL_ERROR_NO_CYPHER_OVERLAP);
	return SECFailure;
	}
	}
	}

	/* we've got the first 3 bytes. The header may be two or three. */
	if (gs->hdr[0] & 0x80) {
	/* This record has a 2-byte header, and no padding */
	gs->count = ((gs->hdr[0] & 0x7f) << 8) \| gs->hdr[1];
	gs->recordPadding = 0;
	} else {
	/* This record has a 3-byte header that is all read in now. */
	gs->count = ((gs->hdr[0] & 0x3f) << 8) \| gs->hdr[1];
	/* is_escape = (gs->hdr[0] & 0x40) != 0; */
	gs->recordPadding = gs->hdr[2];
	}
	if (!gs->count) {
	PORT_SetError(SSL_ERROR_RX_RECORD_TOO_LONG);
	goto cleanup;
	}

	if (gs->count > gs->buf.space) {
	err = sslBuffer_Grow(&gs->buf, gs->count);
	if (err) {
	return err;
	}
	pBuf = gs->buf.buf;
	}

	if (gs->hdr[0] & 0x80) {
	/* we've already read in the first byte of the body.
	** Put it into the buffer.
	*/
	pBuf[0] = gs->hdr[2];
	gs->offset = 1;
	gs->remainder = gs->count - 1;
	} else {
	gs->offset = 0;
	gs->remainder = gs->count;
	}

	if (gs->encrypted) {
	gs->state = GS_MAC;
	gs->recordLen = gs->count - gs->recordPadding -
	ss->sec.hash->length;
	} else {
	gs->state = GS_DATA;
	gs->recordLen = gs->count;
	}

	break;

	case GS_MAC:
	/* Have read in entire rest of the ciphertext.
	** Check for valid length.
	** Decrypt it.
	** Check the MAC.
	*/
	PORT_Assert(gs->encrypted);

	{
	unsigned int macLen;
	int nout;
	unsigned char mac[SSL_MAX_MAC_BYTES];

	ssl_GetSpecReadLock(ss); /**********************************/

	/* If this is a stream cipher, blockSize will be 1,
	* and this test will always be false.
	* If this is a block cipher, this will detect records
	* that are not a multiple of the blocksize in length.
	*/
	if (gs->count & (ss->sec.blockSize - 1)) {
	/* This is an error. Sender is misbehaving */
	SSL_DBG(("%d: SSL[%d]: sender, count=%d blockSize=%d",
	SSL_GETPID(), ss->fd, gs->count,
	ss->sec.blockSize));
	PORT_SetError(SSL_ERROR_BAD_BLOCK_PADDING);
	rv = SECFailure;
	goto spec_locked_done;
	}
	PORT_Assert(gs->count == gs->offset);

	if (gs->offset == 0) {
	rv = 0; /* means EOF. */
	goto spec_locked_done;
	}

	/* Decrypt the portion of data that we just received.
	** Decrypt it in place.
	*/
	rv = (*ss->sec.dec)(ss->sec.readcx, pBuf, &nout, gs->offset,
	pBuf, gs->offset);
	if (rv != SECSuccess) {
	goto spec_locked_done;
	}

	/* Have read in all the MAC portion of record
	**
	** Prepare MAC by resetting it and feeding it the shared secret
	*/
	macLen = ss->sec.hash->length;
	if (gs->offset >= macLen) {
	PRUint32 sequenceNumber = ss->sec.rcvSequence++;
	unsigned char seq[4];

	seq[0] = (unsigned char)(sequenceNumber >> 24);
	seq[1] = (unsigned char)(sequenceNumber >> 16);
	seq[2] = (unsigned char)(sequenceNumber >> 8);
	seq[3] = (unsigned char)(sequenceNumber);

	(*ss->sec.hash->begin)(ss->sec.hashcx);
	(*ss->sec.hash->update)(ss->sec.hashcx, ss->sec.rcvSecret.data,
	ss->sec.rcvSecret.len);
	(*ss->sec.hash->update)(ss->sec.hashcx, pBuf + macLen,
	gs->offset - macLen);
	(*ss->sec.hash->update)(ss->sec.hashcx, seq, 4);
	(*ss->sec.hash->end)(ss->sec.hashcx, mac, &macLen, macLen);

	PORT_Assert(macLen == ss->sec.hash->length);

	ssl_ReleaseSpecReadLock(ss); /******************************/

	if (NSS_SecureMemcmp(mac, pBuf, macLen) != 0) {
	/* MAC's didn't match... */
	SSL_DBG(("%d: SSL[%d]: mac check failed, seq=%d",
	SSL_GETPID(), ss->fd, ss->sec.rcvSequence));
	PRINT_BUF(1, (ss, "computed mac:", mac, macLen));
	PRINT_BUF(1, (ss, "received mac:", pBuf, macLen));
	PORT_SetError(SSL_ERROR_BAD_MAC_READ);
	rv = SECFailure;
	goto cleanup;
	}
	} else {
	ssl_ReleaseSpecReadLock(ss); /******************************/
	}

	if (gs->recordPadding + macLen <= gs->offset) {
	gs->recordOffset = macLen;
	gs->readOffset = macLen;
	gs->writeOffset = gs->offset - gs->recordPadding;
	rv = 1;
	} else {
	PORT_SetError(SSL_ERROR_BAD_BLOCK_PADDING);
	cleanup:
	/* nothing in the buffer any more. */
	gs->recordOffset = 0;
	gs->readOffset = 0;
	gs->writeOffset = 0;
	rv = SECFailure;
	}

	gs->recordLen = gs->writeOffset - gs->readOffset;
	gs->recordPadding = 0; /* forget we did any padding. */
	gs->state = GS_INIT;

	if (rv > 0) {
	PRINT_BUF(50, (ss, "recv clear record:",
	pBuf + gs->recordOffset, gs->recordLen));
	}
	return rv;

	spec_locked_done:
	ssl_ReleaseSpecReadLock(ss);
	return rv;
	}

	case GS_DATA:
	/* Have read in all the DATA portion of record */

	gs->recordOffset = 0;
	gs->readOffset = 0;
	gs->writeOffset = gs->offset;
	PORT_Assert(gs->recordLen == gs->writeOffset - gs->readOffset);
	gs->recordLen = gs->offset;
	gs->recordPadding = 0;
	gs->state = GS_INIT;

	++ss->sec.rcvSequence;

	PRINT_BUF(50, (ss, "recv clear record:",
	pBuf + gs->recordOffset, gs->recordLen));
	return 1;

	} /* end switch gs->state */
	} /* end gather loop. */
	return rv;
	}

	/*
	** Gather a single record of data from the receiving stream. This code
	** first gathers the header (2 or 3 bytes long depending on the value of
	** the most significant bit in the first byte) then gathers up the data
	** for the record into the readBuf. This code handles non-blocking I/O
	** and is to be called multiple times until ss->sec.recordLen != 0.
	*
	* Returns +1 when it has gathered a complete SSLV2 record.
	* Returns 0 if it hits EOF.
	* Returns -1 (SECFailure) on any error
	* Returns -2 (SECWouldBlock)
	*
	* Called by ssl_GatherRecord1stHandshake in sslcon.c,
	* and by DoRecv in sslsecur.c
	* Caller must hold RecvBufLock.
	*/
	int
	ssl2_GatherRecord(sslSocket *ss, int flags)
	{
	return ssl2_GatherData(ss, &ss->gs, flags);
	}

	/* Caller should hold RecvBufLock. */
	SECStatus
	ssl_InitGather(sslGather *gs)
	{
	SECStatus status;

	gs->state = GS_INIT;
	gs->writeOffset = 0;
	gs->readOffset = 0;
	gs->dtlsPacketOffset = 0;
	gs->dtlsPacket.len = 0;
	status = sslBuffer_Grow(&gs->buf, 4096);
	return status;
	}

	/* Caller must hold RecvBufLock. */
	void
	ssl_DestroyGather(sslGather *gs)
	{
	if (gs) { /* the PORT_Free functions check for NULL pointers. /
	PORT_ZFree(gs->buf.buf, gs->buf.space);
	PORT_Free(gs->inbuf.buf);
	PORT_Free(gs->dtlsPacket.buf);
	}
	}

	/* Caller must hold RecvBufLock. */
	static SECStatus
	ssl2_HandleV3HandshakeRecord(sslSocket *ss)
	{
	SECStatus rv;

	PORT_Assert(ss->opt.noLocks \|\| ssl_HaveRecvBufLock(ss));
	PORT_Assert(ss->opt.noLocks \|\| ssl_Have1stHandshakeLock(ss));

	/* We've read in 3 bytes, there are 2 more to go in an ssl3 header. */
	ss->gs.remainder = 2;
	ss->gs.count = 0;

	/* Clearing these handshake pointers ensures that
	* ssl_Do1stHandshake won't call ssl2_HandleMessage when we return.
	*/
	ss->nextHandshake = 0;
	ss->securityHandshake = 0;

	/* Setting ss->version to an SSL 3.x value will cause
	** ssl_GatherRecord1stHandshake to invoke ssl3_GatherCompleteHandshake()
	** the next time it is called.
	**/
	rv = ssl3_NegotiateVersion(ss, SSL_LIBRARY_VERSION_MAX_SUPPORTED,
	PR_TRUE);
	if (rv != SECSuccess) {
	return rv;
	}

	ss->sec.send = ssl3_SendApplicationData;

	return SECSuccess;
	}