- Rename common-packet.c to packet.c

- buf_burn the unencrypted read/write payload buffers after use to avoid
  sensitive contents sitting in memory for too long

1 files changed, 609 insertions, 0 deletions

diff --git a/packet.c b/packet.c
new file mode 100644
index 0000000..886fe67
--- /dev/null
+++ b/packet.c
@@ -0,0 +1,609 @@
+/*
+ * 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;
+	
+	TRACE(("enter write_packet"));
+	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;
+	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) {
+		session_remoteclosed();
+	}
+
+	if (written == len) {
+		/* We've finished with the packet, free it */
+		dequeue(&ses.writequeue);
+		buf_free(writebuf);
+	} 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) */
+	assert(ses.readbuf != NULL);
+	maxlen = ses.readbuf->len - ses.readbuf->pos;
+	len = read(ses.sock, buf_getptr(ses.readbuf, maxlen), maxlen);
+
+	if (len == 0) {
+		session_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);
+		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) {
+		session_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),
+					&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");
+	}
+
+	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),
+						&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 char macsize;
+	hmac_state hmac;
+	unsigned char tempbuf[MAX_MAC_LEN];
+	unsigned long hashsize;
+	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");
+	}
+
+	hashsize = sizeof(tempbuf);
+	if (hmac_done(&hmac, tempbuf, &hashsize) != 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),
+						&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()"));
+}
+
+
+/* Create the packet mac, and append H(seqno|clearbuf) to the output */
+static void writemac(buffer * outputbuffer, buffer * clearwritebuf) {
+
+	int macsize;
+	unsigned char seqbuf[4];
+	unsigned long hashsize;
+	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");
+		}
+	
+		hashsize = macsize;
+		if (hmac_done(&hmac, buf_getwriteptr(outputbuffer, macsize), &hashsize) 
+				!= CRYPT_OK) {
+			dropbear_exit("HMAC error");
+		}
+		buf_incrwritepos(outputbuffer, 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;
+		}
+
+		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