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      1 /*
      2  * Dropbear - a SSH2 server
      3  *
      4  * Copyright (c) 2002-2004 Matt Johnston
      5  * All rights reserved.
      6  *
      7  * Permission is hereby granted, free of charge, to any person obtaining a copy
      8  * of this software and associated documentation files (the "Software"), to deal
      9  * in the Software without restriction, including without limitation the rights
     10  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     11  * copies of the Software, and to permit persons to whom the Software is
     12  * furnished to do so, subject to the following conditions:
     13  *
     14  * The above copyright notice and this permission notice shall be included in
     15  * all copies or substantial portions of the Software.
     16  *
     17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     18  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     19  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
     20  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     21  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
     22  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
     23  * SOFTWARE. */
     24 
     25 #include "includes.h"
     26 #include "packet.h"
     27 #include "session.h"
     28 #include "dbutil.h"
     29 #include "ssh.h"
     30 #include "algo.h"
     31 #include "buffer.h"
     32 #include "kex.h"
     33 #include "random.h"
     34 #include "service.h"
     35 #include "auth.h"
     36 #include "channel.h"
     37 
     38 #define MAX_UNAUTH_PACKET_TYPE SSH_MSG_USERAUTH_PK_OK
     39 
     40 static void recv_unimplemented();
     41 
     42 /* process a decrypted packet, call the appropriate handler */
     43 void process_packet() {
     44 
     45 	unsigned char type;
     46 	unsigned int i;
     47 
     48 	TRACE(("enter process_packet"))
     49 
     50 	type = buf_getbyte(ses.payload);
     51 	TRACE(("process_packet: packet type = %d", type))
     52 
     53 	ses.lastpacket = type;
     54 
     55 	/* These packets we can receive at any time */
     56 	switch(type) {
     57 
     58 		case SSH_MSG_IGNORE:
     59 		case SSH_MSG_DEBUG:
     60 			TRACE(("received SSH_MSG_IGNORE or SSH_MSG_DEBUG"))
     61 			goto out;
     62 
     63 		case SSH_MSG_UNIMPLEMENTED:
     64 			/* debugging XXX */
     65 			TRACE(("SSH_MSG_UNIMPLEMENTED"))
     66 			dropbear_exit("received SSH_MSG_UNIMPLEMENTED");
     67 
     68 		case SSH_MSG_DISCONNECT:
     69 			/* TODO cleanup? */
     70 			dropbear_close("Disconnect received");
     71 	}
     72 
     73 
     74 	/* This applies for KEX, where the spec says the next packet MUST be
     75 	 * NEWKEYS */
     76 	if (ses.requirenext != 0) {
     77 		if (ses.requirenext != type) {
     78 			/* TODO send disconnect? */
     79 			dropbear_exit("unexpected packet type %d, expected %d", type,
     80 					ses.requirenext);
     81 		} else {
     82 			/* Got what we expected */
     83 			ses.requirenext = 0;
     84 		}
     85 	}
     86 
     87 	/* Check if we should ignore this packet. Used currently only for
     88 	 * KEX code, with first_kex_packet_follows */
     89 	if (ses.ignorenext) {
     90 		TRACE(("Ignoring packet, type = %d", type))
     91 		ses.ignorenext = 0;
     92 		goto out;
     93 	}
     94 
     95 
     96 	/* Kindly the protocol authors gave all the preauth packets type values
     97 	 * less-than-or-equal-to 60 ( == MAX_UNAUTH_PACKET_TYPE ).
     98 	 * NOTE: if the protocol changes and new types are added, revisit this
     99 	 * assumption */
    100 	if ( !ses.authstate.authdone && type > MAX_UNAUTH_PACKET_TYPE ) {
    101 		dropbear_exit("received message %d before userauth", type);
    102 	}
    103 
    104 	for (i = 0; ; i++) {
    105 		if (ses.packettypes[i].type == 0) {
    106 			/* end of list */
    107 			break;
    108 		}
    109 
    110 		if (ses.packettypes[i].type == type) {
    111 			ses.packettypes[i].handler();
    112 			goto out;
    113 		}
    114 	}
    115 
    116 
    117 	/* TODO do something more here? */
    118 	TRACE(("preauth unknown packet"))
    119 	recv_unimplemented();
    120 
    121 out:
    122 	buf_free(ses.payload);
    123 	ses.payload = NULL;
    124 
    125 	TRACE(("leave process_packet"))
    126 }
    127 
    128 
    129 
    130 /* This must be called directly after receiving the unimplemented packet.
    131  * Isn't the most clean implementation, it relies on packet processing
    132  * occurring directly after decryption (direct use of ses.recvseq).
    133  * This is reasonably valid, since there is only a single decryption buffer */
    134 static void recv_unimplemented() {
    135 
    136 	CHECKCLEARTOWRITE();
    137 
    138 	buf_putbyte(ses.writepayload, SSH_MSG_UNIMPLEMENTED);
    139 	/* the decryption routine increments the sequence number, we must
    140 	 * decrement */
    141 	buf_putint(ses.writepayload, ses.recvseq - 1);
    142 
    143 	encrypt_packet();
    144 }
    145