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Diffstat (limited to 'packet.c')
| -rw-r--r-- | packet.c | 613 |
1 files changed, 613 insertions, 0 deletions
diff --git a/packet.c b/packet.c new file mode 100644 index 0000000..b2c6174 --- /dev/null +++ b/packet.c @@ -0,0 +1,613 @@ +/* + * Dropbear - a SSH2 server + * + * Copyright (c) 2002,2003 Matt Johnston + * All rights reserved. + * + * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to deal + * in the Software without restriction, including without limitation the rights + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + * copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE + * SOFTWARE. */ + +#include "includes.h" +#include "packet.h" +#include "session.h" +#include "dbutil.h" +#include "ssh.h" +#include "algo.h" +#include "buffer.h" +#include "kex.h" +#include "random.h" +#include "service.h" +#include "auth.h" +#include "channel.h" + +static void read_packet_init(); +static void writemac(buffer * outputbuffer, buffer * clearwritebuf); +static int checkmac(buffer* hashbuf, buffer* readbuf); + +#define ZLIB_COMPRESS_INCR 20 /* this is 12 bytes + 0.1% of 8000 bytes */ +#define ZLIB_DECOMPRESS_INCR 100 +#ifndef DISABLE_ZLIB +static buffer* buf_decompress(buffer* buf, unsigned int len); +static void buf_compress(buffer * dest, buffer * src, unsigned int len); +#endif + +/* non-blocking function writing out a current encrypted packet */ +void write_packet() { + + int len, written; + buffer * writebuf = NULL; + + TRACE(("enter write_packet")) + dropbear_assert(!isempty(&ses.writequeue)); + + /* Get the next buffer in the queue of encrypted packets to write*/ + writebuf = (buffer*)examine(&ses.writequeue); + + len = writebuf->len - writebuf->pos; + dropbear_assert(len > 0); + /* Try to write as much as possible */ + written = write(ses.sock, buf_getptr(writebuf, len), len); + + if (written < 0) { + if (errno == EINTR) { + TRACE(("leave writepacket: EINTR")) + return; + } else { + dropbear_exit("error writing"); + } + } + + if (written == 0) { + ses.remoteclosed(); + } + + if (written == len) { + /* We've finished with the packet, free it */ + dequeue(&ses.writequeue); + buf_free(writebuf); + writebuf = NULL; + } else { + /* More packet left to write, leave it in the queue for later */ + buf_incrpos(writebuf, written); + } + + TRACE(("leave write_packet")) +} + +/* Non-blocking function reading available portion of a packet into the + * ses's buffer, decrypting the length if encrypted, decrypting the + * full portion if possible */ +void read_packet() { + + int len; + unsigned int maxlen; + unsigned char blocksize; + + TRACE(("enter read_packet")) + blocksize = ses.keys->recv_algo_crypt->blocksize; + + if (ses.readbuf == NULL || ses.readbuf->len < blocksize) { + /* In the first blocksize of a packet */ + + /* Read the first blocksize of the packet, so we can decrypt it and + * find the length of the whole packet */ + read_packet_init(); + + /* If we don't have the length of decryptreadbuf, we didn't read + * a whole blocksize and should exit */ + if (ses.decryptreadbuf->len == 0) { + TRACE(("leave read_packet: packetinit done")) + return; + } + } + + /* Attempt to read the remainder of the packet, note that there + * mightn't be any available (EAGAIN) */ + dropbear_assert(ses.readbuf != NULL); + maxlen = ses.readbuf->len - ses.readbuf->pos; + len = read(ses.sock, buf_getptr(ses.readbuf, maxlen), maxlen); + + if (len == 0) { + ses.remoteclosed(); + } + + if (len < 0) { + if (errno == EINTR || errno == EAGAIN) { + TRACE(("leave read_packet: EINTR or EAGAIN")) + return; + } else { + dropbear_exit("error reading: %s", strerror(errno)); + } + } + + buf_incrpos(ses.readbuf, len); + + if ((unsigned int)len == maxlen) { + /* The whole packet has been read */ + decrypt_packet(); + /* The main select() loop process_packet() to + * handle the packet contents... */ + } + TRACE(("leave read_packet")) +} + +/* Function used to read the initial portion of a packet, and determine the + * length. Only called during the first BLOCKSIZE of a packet. */ +static void read_packet_init() { + + unsigned int maxlen; + int len; + unsigned char blocksize; + unsigned char macsize; + + + blocksize = ses.keys->recv_algo_crypt->blocksize; + macsize = ses.keys->recv_algo_mac->hashsize; + + if (ses.readbuf == NULL) { + /* start of a new packet */ + ses.readbuf = buf_new(INIT_READBUF); + dropbear_assert(ses.decryptreadbuf == NULL); + ses.decryptreadbuf = buf_new(blocksize); + } + + maxlen = blocksize - ses.readbuf->pos; + + /* read the rest of the packet if possible */ + len = read(ses.sock, buf_getwriteptr(ses.readbuf, maxlen), + maxlen); + if (len == 0) { + ses.remoteclosed(); + } + if (len < 0) { + if (errno == EINTR) { + TRACE(("leave read_packet_init: EINTR")) + return; + } + dropbear_exit("error reading: %s", strerror(errno)); + } + + buf_incrwritepos(ses.readbuf, len); + + if ((unsigned int)len != maxlen) { + /* don't have enough bytes to determine length, get next time */ + return; + } + + /* now we have the first block, need to get packet length, so we decrypt + * the first block (only need first 4 bytes) */ + buf_setpos(ses.readbuf, 0); + if (ses.keys->recv_algo_crypt->cipherdesc == NULL) { + /* copy it */ + memcpy(buf_getwriteptr(ses.decryptreadbuf, blocksize), + buf_getptr(ses.readbuf, blocksize), + blocksize); + } else { + /* decrypt it */ + if (cbc_decrypt(buf_getptr(ses.readbuf, blocksize), + buf_getwriteptr(ses.decryptreadbuf,blocksize), + blocksize, + &ses.keys->recv_symmetric_struct) != CRYPT_OK) { + dropbear_exit("error decrypting"); + } + } + buf_setlen(ses.decryptreadbuf, blocksize); + len = buf_getint(ses.decryptreadbuf) + 4 + macsize; + + buf_setpos(ses.readbuf, blocksize); + + /* check packet length */ + if ((len > MAX_PACKET_LEN) || + (len < MIN_PACKET_LEN + macsize) || + ((len - macsize) % blocksize != 0)) { + dropbear_exit("bad packet size %d", len); + } + + buf_resize(ses.readbuf, len); + buf_setlen(ses.readbuf, len); + +} + +/* handle the received packet */ +void decrypt_packet() { + + unsigned char blocksize; + unsigned char macsize; + unsigned int padlen; + unsigned int len; + + TRACE(("enter decrypt_packet")) + blocksize = ses.keys->recv_algo_crypt->blocksize; + macsize = ses.keys->recv_algo_mac->hashsize; + + ses.kexstate.datarecv += ses.readbuf->len; + + /* we've already decrypted the first blocksize in read_packet_init */ + buf_setpos(ses.readbuf, blocksize); + + buf_resize(ses.decryptreadbuf, ses.readbuf->len - macsize); + buf_setlen(ses.decryptreadbuf, ses.decryptreadbuf->size); + buf_setpos(ses.decryptreadbuf, blocksize); + + /* decrypt if encryption is set, memcpy otherwise */ + if (ses.keys->recv_algo_crypt->cipherdesc == NULL) { + /* copy it */ + len = ses.readbuf->len - macsize - blocksize; + memcpy(buf_getwriteptr(ses.decryptreadbuf, len), + buf_getptr(ses.readbuf, len), len); + } else { + /* decrypt */ + while (ses.readbuf->pos < ses.readbuf->len - macsize) { + if (cbc_decrypt(buf_getptr(ses.readbuf, blocksize), + buf_getwriteptr(ses.decryptreadbuf, blocksize), + blocksize, + &ses.keys->recv_symmetric_struct) != CRYPT_OK) { + dropbear_exit("error decrypting"); + } + buf_incrpos(ses.readbuf, blocksize); + buf_incrwritepos(ses.decryptreadbuf, blocksize); + } + } + + /* check the hmac */ + buf_setpos(ses.readbuf, ses.readbuf->len - macsize); + if (checkmac(ses.readbuf, ses.decryptreadbuf) != DROPBEAR_SUCCESS) { + dropbear_exit("Integrity error"); + } + + /* readbuf no longer required */ + buf_free(ses.readbuf); + ses.readbuf = NULL; + + /* get padding length */ + buf_setpos(ses.decryptreadbuf, PACKET_PADDING_OFF); + padlen = buf_getbyte(ses.decryptreadbuf); + + /* payload length */ + /* - 4 - 1 is for LEN and PADLEN values */ + len = ses.decryptreadbuf->len - padlen - 4 - 1; + if ((len > MAX_PAYLOAD_LEN) || (len < 1)) { + dropbear_exit("bad packet size"); + } + + buf_setpos(ses.decryptreadbuf, PACKET_PAYLOAD_OFF); + +#ifndef DISABLE_ZLIB + if (ses.keys->recv_algo_comp == DROPBEAR_COMP_ZLIB) { + /* decompress */ + ses.payload = buf_decompress(ses.decryptreadbuf, len); + + } else +#endif + { + /* copy payload */ + ses.payload = buf_new(len); + memcpy(ses.payload->data, buf_getptr(ses.decryptreadbuf, len), len); + buf_incrlen(ses.payload, len); + } + + buf_free(ses.decryptreadbuf); + ses.decryptreadbuf = NULL; + buf_setpos(ses.payload, 0); + + ses.recvseq++; + + TRACE(("leave decrypt_packet")) +} + +/* Checks the mac in hashbuf, for the data in readbuf. + * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */ +static int checkmac(buffer* macbuf, buffer* sourcebuf) { + + unsigned int macsize; + hmac_state hmac; + unsigned char tempbuf[MAX_MAC_LEN]; + unsigned long bufsize; + unsigned int len; + + macsize = ses.keys->recv_algo_mac->hashsize; + if (macsize == 0) { + return DROPBEAR_SUCCESS; + } + + /* calculate the mac */ + if (hmac_init(&hmac, + find_hash(ses.keys->recv_algo_mac->hashdesc->name), + ses.keys->recvmackey, + ses.keys->recv_algo_mac->keysize) + != CRYPT_OK) { + dropbear_exit("HMAC error"); + } + + /* sequence number */ + STORE32H(ses.recvseq, tempbuf); + if (hmac_process(&hmac, tempbuf, 4) != CRYPT_OK) { + dropbear_exit("HMAC error"); + } + + buf_setpos(sourcebuf, 0); + len = sourcebuf->len; + if (hmac_process(&hmac, buf_getptr(sourcebuf, len), len) != CRYPT_OK) { + dropbear_exit("HMAC error"); + } + + bufsize = sizeof(tempbuf); + if (hmac_done(&hmac, tempbuf, &bufsize) != CRYPT_OK) { + dropbear_exit("HMAC error"); + } + + /* compare the hash */ + if (memcmp(tempbuf, buf_getptr(macbuf, macsize), macsize) != 0) { + return DROPBEAR_FAILURE; + } else { + return DROPBEAR_SUCCESS; + } +} + +#ifndef DISABLE_ZLIB +/* returns a pointer to a newly created buffer */ +static buffer* buf_decompress(buffer* buf, unsigned int len) { + + int result; + buffer * ret; + z_streamp zstream; + + zstream = ses.keys->recv_zstream; + ret = buf_new(len); + + zstream->avail_in = len; + zstream->next_in = buf_getptr(buf, len); + + /* decompress the payload, incrementally resizing the output buffer */ + while (1) { + + zstream->avail_out = ret->size - ret->pos; + zstream->next_out = buf_getwriteptr(ret, zstream->avail_out); + + result = inflate(zstream, Z_SYNC_FLUSH); + + buf_setlen(ret, ret->size - zstream->avail_out); + buf_setpos(ret, ret->len); + + if (result != Z_BUF_ERROR && result != Z_OK) { + dropbear_exit("zlib error"); + } + + if (zstream->avail_in == 0 && + (zstream->avail_out != 0 || result == Z_BUF_ERROR)) { + /* we can only exit if avail_out hasn't all been used, + * and there's no remaining input */ + return ret; + } + + if (zstream->avail_out == 0) { + buf_resize(ret, ret->size + ZLIB_DECOMPRESS_INCR); + } + } +} +#endif + + + + +/* encrypt the writepayload, putting into writebuf, ready for write_packet() + * to put on the wire */ +void encrypt_packet() { + + unsigned char padlen; + unsigned char blocksize, macsize; + buffer * writebuf; /* the packet which will go on the wire */ + buffer * clearwritebuf; /* unencrypted, possibly compressed */ + + TRACE(("enter encrypt_packet()")) + TRACE(("encrypt_packet type is %d", ses.writepayload->data[0])) + blocksize = ses.keys->trans_algo_crypt->blocksize; + macsize = ses.keys->trans_algo_mac->hashsize; + + /* Encrypted packet len is payload+5, then worst case is if we are 3 away + * from a blocksize multiple. In which case we need to pad to the + * multiple, then add another blocksize (or MIN_PACKET_LEN) */ + clearwritebuf = buf_new((ses.writepayload->len+4+1) + MIN_PACKET_LEN + 3 +#ifndef DISABLE_ZLIB + + ZLIB_COMPRESS_INCR /* bit of a kludge, but we can't know len*/ +#endif + ); + buf_setlen(clearwritebuf, PACKET_PAYLOAD_OFF); + buf_setpos(clearwritebuf, PACKET_PAYLOAD_OFF); + + buf_setpos(ses.writepayload, 0); + +#ifndef DISABLE_ZLIB + /* compression */ + if (ses.keys->trans_algo_comp == DROPBEAR_COMP_ZLIB) { + buf_compress(clearwritebuf, ses.writepayload, ses.writepayload->len); + } else +#endif + { + memcpy(buf_getwriteptr(clearwritebuf, ses.writepayload->len), + buf_getptr(ses.writepayload, ses.writepayload->len), + ses.writepayload->len); + buf_incrwritepos(clearwritebuf, ses.writepayload->len); + } + + /* finished with payload */ + buf_burn(ses.writepayload); /* XXX This is probably a good idea, and isn't + _that_ likely to hurt performance too badly. + Buffers can have cleartext passwords etc, or + other sensitive data */ + buf_setpos(ses.writepayload, 0); + buf_setlen(ses.writepayload, 0); + + /* length of padding - packet length must be a multiple of blocksize, + * with a minimum of 4 bytes of padding */ + padlen = blocksize - (clearwritebuf->len) % blocksize; + if (padlen < 4) { + padlen += blocksize; + } + /* check for min packet length */ + if (clearwritebuf->len + padlen < MIN_PACKET_LEN) { + padlen += blocksize; + } + + buf_setpos(clearwritebuf, 0); + /* packet length excluding the packetlength uint32 */ + buf_putint(clearwritebuf, clearwritebuf->len + padlen - 4); + + /* padding len */ + buf_putbyte(clearwritebuf, padlen); + /* actual padding */ + buf_setpos(clearwritebuf, clearwritebuf->len); + buf_incrlen(clearwritebuf, padlen); + genrandom(buf_getptr(clearwritebuf, padlen), padlen); + + /* do the actual encryption */ + buf_setpos(clearwritebuf, 0); + /* create a new writebuffer, this is freed when it has been put on the + * wire by writepacket() */ + writebuf = buf_new(clearwritebuf->len + macsize); + + if (ses.keys->trans_algo_crypt->cipherdesc == NULL) { + /* copy it */ + memcpy(buf_getwriteptr(writebuf, clearwritebuf->len), + buf_getptr(clearwritebuf, clearwritebuf->len), + clearwritebuf->len); + buf_incrwritepos(writebuf, clearwritebuf->len); + } else { + /* encrypt it */ + while (clearwritebuf->pos < clearwritebuf->len) { + if (cbc_encrypt(buf_getptr(clearwritebuf, blocksize), + buf_getwriteptr(writebuf, blocksize), + blocksize, + &ses.keys->trans_symmetric_struct) != CRYPT_OK) { + dropbear_exit("error encrypting"); + } + buf_incrpos(clearwritebuf, blocksize); + buf_incrwritepos(writebuf, blocksize); + } + } + + /* now add a hmac and we're done */ + writemac(writebuf, clearwritebuf); + + /* clearwritebuf is finished with */ + buf_free(clearwritebuf); + clearwritebuf = NULL; + + /* enqueue the packet for sending */ + buf_setpos(writebuf, 0); + enqueue(&ses.writequeue, (void*)writebuf); + + /* Update counts */ + ses.kexstate.datatrans += writebuf->len; + ses.transseq++; + + TRACE(("leave encrypt_packet()")) +} + + +/* Create the packet mac, and append H(seqno|clearbuf) to the output */ +static void writemac(buffer * outputbuffer, buffer * clearwritebuf) { + + unsigned int macsize; + unsigned char seqbuf[4]; + unsigned char tempbuf[MAX_MAC_LEN]; + unsigned long bufsize; + hmac_state hmac; + + TRACE(("enter writemac")) + + macsize = ses.keys->trans_algo_mac->hashsize; + if (macsize > 0) { + /* calculate the mac */ + if (hmac_init(&hmac, + find_hash(ses.keys->trans_algo_mac->hashdesc->name), + ses.keys->transmackey, + ses.keys->trans_algo_mac->keysize) != CRYPT_OK) { + dropbear_exit("HMAC error"); + } + + /* sequence number */ + STORE32H(ses.transseq, seqbuf); + if (hmac_process(&hmac, seqbuf, 4) != CRYPT_OK) { + dropbear_exit("HMAC error"); + } + + /* the actual contents */ + buf_setpos(clearwritebuf, 0); + if (hmac_process(&hmac, + buf_getptr(clearwritebuf, + clearwritebuf->len), + clearwritebuf->len) != CRYPT_OK) { + dropbear_exit("HMAC error"); + } + + bufsize = sizeof(tempbuf); + if (hmac_done(&hmac, tempbuf, &bufsize) + != CRYPT_OK) { + dropbear_exit("HMAC error"); + } + buf_putbytes(outputbuffer, tempbuf, macsize); + } + TRACE(("leave writemac")) +} + +#ifndef DISABLE_ZLIB +/* compresses len bytes from src, outputting to dest (starting from the + * respective current positions. */ +static void buf_compress(buffer * dest, buffer * src, unsigned int len) { + + unsigned int endpos = src->pos + len; + int result; + + TRACE(("enter buf_compress")) + + while (1) { + + ses.keys->trans_zstream->avail_in = endpos - src->pos; + ses.keys->trans_zstream->next_in = + buf_getptr(src, ses.keys->trans_zstream->avail_in); + + ses.keys->trans_zstream->avail_out = dest->size - dest->pos; + ses.keys->trans_zstream->next_out = + buf_getwriteptr(dest, ses.keys->trans_zstream->avail_out); + + result = deflate(ses.keys->trans_zstream, Z_SYNC_FLUSH); + + buf_setpos(src, endpos - ses.keys->trans_zstream->avail_in); + buf_setlen(dest, dest->size - ses.keys->trans_zstream->avail_out); + buf_setpos(dest, dest->len); + + if (result != Z_OK) { + dropbear_exit("zlib error"); + } + + if (ses.keys->trans_zstream->avail_in == 0) { + break; + } + + dropbear_assert(ses.keys->trans_zstream->avail_out == 0); + + /* the buffer has been filled, we must extend. This only happens in + * unusual circumstances where the data grows in size after deflate(), + * but it is possible */ + buf_resize(dest, dest->size + ZLIB_COMPRESS_INCR); + + } + TRACE(("leave buf_compress")) +} +#endif |