/* put a byte, incrementing the length if required */
void buf_putbyte(buffer* buf, unsigned char val) {
if (buf->pos >= buf->len) {
buf_incrlen(buf, 1);
}
buf->data[buf->pos] = val;
buf->pos++;
}
/* Return a string as a newly allocated buffer */
buffer * buf_getstringbuf(buffer *buf) {
buffer *ret = NULL;
unsigned int len = buf_getint(buf);
if (len > MAX_STRING_LEN) {
dropbear_exit("String too long");
}
ret = buf_new(len);
memcpy(buf_getwriteptr(ret, len), buf_getptr(buf, len), len);
buf_incrpos(buf, len);
buf_incrlen(ret, len);
return ret;
}
/* 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_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),
&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);
/* 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()"));
}
/* 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),
&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"));
}
/* Reads data from the server's program/shell/etc, and puts it in a
* channel_data packet to send.
* chan is the remote channel, isextended is 0 if it is normal data, 1
* if it is extended data. if it is extended, then the type is in
* exttype */
static void send_msg_channel_data(struct Channel *channel, int isextended,
unsigned int exttype) {
buffer *buf;
int len;
unsigned int maxlen;
int fd;
TRACE(("enter send_msg_channel_data"));
TRACE(("extended = %d type = %d", isextended, exttype));
CHECKCLEARTOWRITE();
assert(!channel->sentclosed);
if (isextended) {
if (channel->erreof) {
TRACE(("leave send_msg_channel_data: erreof already set"));
return;
}
assert(exttype == SSH_EXTENDED_DATA_STDERR);
fd = channel->errfd;
} else {
if (channel->transeof) {
TRACE(("leave send_msg_channel_data: transeof already set"));
return;
}
fd = channel->outfd;
}
assert(fd >= 0);
maxlen = MIN(channel->transwindow, channel->transmaxpacket);
/* -(1+4+4) is SSH_MSG_CHANNEL_DATA, channel number, string length, and
* exttype if is extended */
maxlen = MIN(maxlen, ses.writepayload->size
- 1 - 4 - 4 - (isextended ? 4 : 0));
if (maxlen == 0) {
TRACE(("leave send_msg_channel_data: no window"));
return; /* the data will get written later */
}
/* read the data */
buf = buf_new(maxlen);
len = read(fd, buf_getwriteptr(buf, maxlen), maxlen);
if (len <= 0) {
/* on error etc, send eof */
if (errno != EINTR) {
if (isextended) {
channel->erreof = 1;
} else {
channel->transeof = 1;
}
if ((channel->erreof || channel->errfd == -1)
&& channel->transeof) {
send_msg_channel_eof(channel);
}
}
buf_free(buf);
TRACE(("leave send_msg_channel_data: len <= 0, erreof %d transeof %d",
channel->erreof, channel->transeof));
return;
}
buf_incrlen(buf, len);
buf_putbyte(ses.writepayload,
isextended ? SSH_MSG_CHANNEL_EXTENDED_DATA : SSH_MSG_CHANNEL_DATA);
buf_putint(ses.writepayload, channel->remotechan);
if (isextended) {
buf_putint(ses.writepayload, exttype);
}
buf_putstring(ses.writepayload, buf_getptr(buf, len), len);
buf_free(buf);
channel->transwindow -= len;
encrypt_packet();
TRACE(("leave send_msg_channel_data"));
}