networking/tftp.c

/* vi: set sw=4 ts=4: */
/* -------------------------------------------------------------------------
 * tftp.c
 *
 * A simple tftp client/server for busybox.
 * Tries to follow RFC1350.
 * Only "octet" mode supported.
 * Optional blocksize negotiation (RFC2347 + RFC2348)
 *
 * Copyright (C) 2001 Magnus Damm <damm@opensource.se>
 *
 * Parts of the code based on:
 *
 * atftp:  Copyright (C) 2000 Jean-Pierre Lefebvre <helix@step.polymtl.ca>
 *                        and Remi Lefebvre <remi@debian.org>
 *
 * utftp:  Copyright (C) 1999 Uwe Ohse <uwe@ohse.de>
 *
 * tftpd added by Denys Vlasenko
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 * ------------------------------------------------------------------------- */

#include "libbb.h"

#if ENABLE_FEATURE_TFTP_GET || ENABLE_FEATURE_TFTP_PUT

#define TFTP_BLOCKSIZE_DEFAULT 512      /* according to RFC 1350, don't change */
#define TFTP_TIMEOUT_MS         50
#define TFTP_MAXTIMEOUT_MS    2000
#define TFTP_NUM_RETRIES        12      /* number of backed-off retries */

/* opcodes we support */
#define TFTP_RRQ   1
#define TFTP_WRQ   2
#define TFTP_DATA  3
#define TFTP_ACK   4
#define TFTP_ERROR 5
#define TFTP_OACK  6

#if ENABLE_FEATURE_TFTP_GET && !ENABLE_FEATURE_TFTP_PUT
#define USE_GETPUT(...)
#define CMD_GET(cmd) 1
#define CMD_PUT(cmd) 0
#elif !ENABLE_FEATURE_TFTP_GET && ENABLE_FEATURE_TFTP_PUT
#define USE_GETPUT(...)
#define CMD_GET(cmd) 0
#define CMD_PUT(cmd) 1
#else
#define USE_GETPUT(...) __VA_ARGS__
/* masks coming from getopt32 */
#define CMD_GET(cmd) ((cmd) & 1)
#define CMD_PUT(cmd) ((cmd) & 2)
#endif
/* NB: in the code below
 * CMD_GET(cmd) and CMD_PUT(cmd) are mutually exclusive
 */


#if ENABLE_FEATURE_TFTP_BLOCKSIZE

static int tftp_blocksize_check(int blocksize, int bufsize)
{
	/* Check if the blocksize is valid:
	 * RFC2348 says between 8 and 65464,
	 * but our implementation makes it impossible
	 * to use blocksizes smaller than 22 octets.
	 */
	if ((bufsize && (blocksize > bufsize))
	 || (blocksize < 24) || (blocksize > 65564)
	) {
		bb_error_msg("bad blocksize");
		return 0;
	}
	return blocksize;
}

static char *tftp_option_get(char *buf, int len, const char *option)
{
	int opt_val = 0;
	int opt_found = 0;
	int k;

	/* buf points to:
	 * "opt_name<NUL>opt_val<NUL>opt_name2<NUL>opt_val2<NUL>..." */

	while (len > 0) {
		/* Make sure options are terminated correctly */
		for (k = 0; k < len; k++) {
			if (buf[k] == '\0') {
				goto nul_found;
			}
		}
		return NULL;
 nul_found:
		if (opt_val == 0) { /* it's "name" part */
			if (strcasecmp(buf, option) == 0) {
				opt_found = 1;
			}
		} else if (opt_found) {
			return buf;
		}

		k++;
		buf += k;
		len -= k;
		opt_val ^= 1;
	}

	return NULL;
}

#endif

static int tftp_protocol(
		USE_GETPUT(int cmd,)
		len_and_sockaddr *our_lsa,
		len_and_sockaddr *peer_lsa,
		USE_TFTP(const char *remote_file,)
		int local_fd,
		int blocksize)
{
#if !ENABLE_TFTP
#define remote_file NULL
#endif
	struct pollfd pfd[1];
#define socket_fd (pfd[0].fd)
	int len;
	int send_len;
	USE_FEATURE_TFTP_BLOCKSIZE(smallint want_option_ack = 0;)
	smallint finished = 0;
	uint16_t opcode;
	uint16_t block_nr;
	uint16_t recv_blk;
	int retries, waittime_ms;
	int tftp_bufsize = blocksize + 4;
	char *cp;
	/* Can't use RESERVE_CONFIG_BUFFER here since the allocation
	 * size varies meaning BUFFERS_GO_ON_STACK would fail */
	/* We must keep the transmit and receive buffers seperate */
	/* In case we rcv a garbage pkt and we need to rexmit the last pkt */
	char *xbuf = xmalloc(tftp_bufsize);
	char *rbuf = xmalloc(tftp_bufsize);

	socket_fd = xsocket(peer_lsa->u.sa.sa_family, SOCK_DGRAM, 0);
	setsockopt_reuseaddr(socket_fd);

	if (!ENABLE_TFTP || our_lsa) {
		/* tftpd */
		block_nr = 0;

		/* Create a socket which is:
		 * 1. bound to IP:port peer sent 1st datagram to,
		 * 2. connected to peer's IP:port
		 * This way we will answer from the IP:port peer
		 * expects, will not get any other packets on
		 * the socket, and also plain read/write will work. */
		xbind(socket_fd, &our_lsa->u.sa, our_lsa->len);
		xconnect(socket_fd, &peer_lsa->u.sa, peer_lsa->len);

#if ENABLE_FEATURE_TFTP_BLOCKSIZE
		if (blocksize != TFTP_BLOCKSIZE_DEFAULT) {
			/* Create and send OACK packet */
			opcode = TFTP_OACK;
			cp = xbuf + 2;
			goto add_blksize_opt;
		}
		/* else: just fall into while (1) loop below */
#endif
	} else {
		/* tftp */
		block_nr = 1;

		/* We can't (and don't really need to) bind the socket:
		 * we don't know from which local IP datagrams will be sent,
		 * but kernel will pick the same IP every time (unless routing
		 * table is changed), thus peer will see dgrams consistently
		 * coming from the same IP.
		 * We would like to connect the socket, but since peer's
		 * UDP code can be less perfect than ours, _peer's_ IP:port
		 * in replies may differ from IP:port we used to send
		 * our first packet. We can connect() only when we get
		 * first reply. */

		/* build opcode */
		opcode = TFTP_WRQ;
		if (CMD_GET(cmd)) {
			opcode = TFTP_RRQ;
		}
		cp = xbuf + 2;
		/* add filename and mode */
		/* fill in packet if the filename fits into xbuf */
		len = strlen(remote_file) + 1;
		if (2 + len + sizeof("octet") >= tftp_bufsize) {
			bb_error_msg("remote filename is too long");
			goto ret;
		}
		strcpy(cp, remote_file);
		cp += len;
		/* add "mode" part of the package */
		strcpy(cp, "octet");
		cp += sizeof("octet");

#if ENABLE_FEATURE_TFTP_BLOCKSIZE
		if (blocksize != TFTP_BLOCKSIZE_DEFAULT) {
			/* rfc2348 says that 65464 is a max allowed value */
			if ((&xbuf[tftp_bufsize - 1] - cp) < sizeof("blksize NNNNN")) {
				bb_error_msg("remote filename is too long");
				goto ret;
			}
			want_option_ack = 1;
 add_blksize_opt:
			/* add "blksize", <nul>, blocksize, <nul> */
			strcpy(cp, "blksize");
			cp += sizeof("blksize");
			cp += snprintf(cp, 6, "%d", blocksize) + 1;
		}
#endif
		/* First packet is built, so skip packet generation */
		goto send_pkt;
	}

	/* Using mostly goto's - continue/break will be less clear
	 * in where we actually jump to */
	while (1) {
		/* Build ACK or DATA */
		cp = xbuf + 2;
		*((uint16_t*)cp) = htons(block_nr);
		cp += 2;
		block_nr++;
		opcode = TFTP_ACK;
		if (CMD_PUT(cmd)) {
			opcode = TFTP_DATA;
			len = full_read(local_fd, cp, tftp_bufsize - 4);
			if (len < 0) {
				bb_perror_msg(bb_msg_read_error);
				goto ret;
			}
			if (len != (tftp_bufsize - 4)) {
				finished = 1;
			}
			cp += len;
		}
 send_pkt:
		/* Send packet */
		*((uint16_t*)xbuf) = htons(opcode); /* fill in opcode part */
		send_len = cp - xbuf;
		/* NB: send_len value is preserved in code below
		 * for potential resend */

		retries = TFTP_NUM_RETRIES;	/* re-initialize */
		waittime_ms = TFTP_TIMEOUT_MS;

 send_again:
#if ENABLE_DEBUG_TFTP
		fprintf(stderr, "sending %u bytes\n", send_len);
		for (cp = xbuf; cp < &xbuf[send_len]; cp++)
			fprintf(stderr, "%02x ", (unsigned char) *cp);
		fprintf(stderr, "\n");
#endif
		xsendto(socket_fd, xbuf, send_len, &peer_lsa->u.sa, peer_lsa->len);
		/* Was it final ACK? then exit */
		if (finished && (opcode == TFTP_ACK))
			goto ret;

 recv_again:
		/* Receive packet */
		/*pfd[0].fd = socket_fd;*/
		pfd[0].events = POLLIN;
		switch (safe_poll(pfd, 1, waittime_ms)) {
		case 1:
			if (!our_lsa) {
				/* tftp (not tftpd!) receiving 1st packet */
				our_lsa = ((void*)(ptrdiff_t)-1); /* not NULL */
				len = recvfrom(socket_fd, rbuf, tftp_bufsize, 0,
						&peer_lsa->u.sa, &peer_lsa->len);
				/* Our first dgram went to port 69
				 * but reply may come from different one.
				 * Remember and use this new port (and IP) */
				if (len >= 0)
					xconnect(socket_fd, &peer_lsa->u.sa, peer_lsa->len);
			} else {
				/* tftpd, or not the very first packet:
				 * socket is connect()ed, can just read from it. */
				len = safe_read(socket_fd, rbuf, tftp_bufsize);
			}
			if (len < 0) {
				bb_perror_msg("read");
				goto ret;
			}
			goto process_pkt;
		case 0:
			retries--;
			if (retries == 0) {
				bb_error_msg("timeout");
				goto ret;
			}

			/* exponential backoff with limit */
			waittime_ms += waittime_ms/2;
			if (waittime_ms > TFTP_MAXTIMEOUT_MS) {
				waittime_ms = TFTP_MAXTIMEOUT_MS;
			}

			goto send_again; /* resend last sent pkt */
		default:
			/*bb_perror_msg("poll"); - done in safe_poll */
			goto ret;
		}
 process_pkt:
		/* Process recv'ed packet */
		opcode = ntohs( ((uint16_t*)rbuf)[0] );
		recv_blk = ntohs( ((uint16_t*)rbuf)[1] );

#if ENABLE_DEBUG_TFTP
		fprintf(stderr, "received %d bytes: %04x %04x\n", len, opcode, recv_blk);
#endif

		if (opcode == TFTP_ERROR) {
			static const char *const errcode_str[] = {
				"",
				"file not found",
				"access violation",
				"disk full",
				"illegal TFTP operation",
				"unknown transfer id",
				"file already exists",
				"no such user",
				"bad option"
			};

			const char *msg = "";

			if (rbuf[4] != '\0') {
				msg = &rbuf[4];
				rbuf[tftp_bufsize - 1] = '\0';
			} else if (recv_blk < ARRAY_SIZE(errcode_str)) {
				msg = errcode_str[recv_blk];
			}
			bb_error_msg("server error: (%u) %s", recv_blk, msg);
			goto ret;
		}

#if ENABLE_FEATURE_TFTP_BLOCKSIZE
		if (want_option_ack) {
			want_option_ack = 0;

			if (opcode == TFTP_OACK) {
				/* server seems to support options */
				char *res;

				res = tftp_option_get(&rbuf[2], len - 2, "blksize");
				if (res) {
					int blksize = xatoi_u(res);
					if (!tftp_blocksize_check(blksize, tftp_bufsize - 4)) {
						/* send ERROR 8 to server... */
						/* htons can be impossible to use in const initializer: */
						/*static const uint16_t error_8[2] = { htons(TFTP_ERROR), htons(8) };*/
						/* thus we open-code big-endian layout */
						static const uint8_t error_8[4] = { 0,TFTP_ERROR, 0,8 };
						xsendto(socket_fd, error_8, 4, &peer_lsa->u.sa, peer_lsa->len);
						bb_error_msg("server proposes bad blksize %d, exiting", blksize);
						goto ret;
					}
#if ENABLE_DEBUG_TFTP
					fprintf(stderr, "using blksize %u\n",
							blksize);
#endif
					tftp_bufsize = blksize + 4;
					/* Send ACK for OACK ("block" no: 0) */
					block_nr = 0;
					continue;
				}
				/* rfc2347:
				 * "An option not acknowledged by the server
				 *  must be ignored by the client and server
				 *  as if it were never requested." */
			}

			bb_error_msg("blksize is not supported by server"
						" - reverting to 512");
			tftp_bufsize = TFTP_BLOCKSIZE_DEFAULT + 4;
		}
#endif
		/* block_nr is already advanced to next block# we expect
		 * to get / block# we are about to send next time */

		if (CMD_GET(cmd) && (opcode == TFTP_DATA)) {
			if (recv_blk == block_nr) {
				len = full_write(local_fd, &rbuf[4], len - 4);
				if (len < 0) {
					bb_perror_msg(bb_msg_write_error);
					goto ret;
				}
				if (len != (tftp_bufsize - 4)) {
					finished = 1;
				}
				continue; /* send ACK */
			}
			if (recv_blk == (block_nr - 1)) {
				/* Server lost our TFTP_ACK.  Resend it */
				block_nr = recv_blk;
				continue;
			}
		}

		if (CMD_PUT(cmd) && (opcode == TFTP_ACK)) {
			/* did peer ACK our last DATA pkt? */
			if (recv_blk == (uint16_t) (block_nr - 1)) {
				if (finished)
					goto ret;
				continue; /* send next block */
			}
		}
		/* Awww... recv'd packet is not recognized! */
		goto recv_again;
		/* why recv_again? - rfc1123 says:
		 * "The sender (i.e., the side originating the DATA packets)
		 *  must never resend the current DATA packet on receipt
		 *  of a duplicate ACK".
		 * DATA pkts are resent ONLY on timeout.
		 * Thus "goto send_again" will ba a bad mistake above.
		 * See:
		 * http://en.wikipedia.org/wiki/Sorcerer's_Apprentice_Syndrome
		 */
	} /* end of "while (1)" */
 ret:
	if (ENABLE_FEATURE_CLEAN_UP) {
		close(socket_fd);
		free(xbuf);
		free(rbuf);
	}
	return finished == 0; /* returns 1 on failure */
}

#if ENABLE_TFTP

int tftp_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int tftp_main(int argc ATTRIBUTE_UNUSED, char **argv)
{
	len_and_sockaddr *peer_lsa;
	const char *local_file = NULL;
	const char *remote_file = NULL;
	int port;
	USE_GETPUT(int cmd;)
	int local_fd;
	int flags = 0;
	int result;
	int blocksize = TFTP_BLOCKSIZE_DEFAULT;

	/* -p or -g is mandatory, and they are mutually exclusive */
	opt_complementary = "" USE_FEATURE_TFTP_GET("g:") USE_FEATURE_TFTP_PUT("p:")
			USE_GETPUT("g--p:p--g:")
			USE_FEATURE_TFTP_BLOCKSIZE("b+");

	USE_GETPUT(cmd =) getopt32(argv,
			USE_FEATURE_TFTP_GET("g") USE_FEATURE_TFTP_PUT("p")
				"l:r:" USE_FEATURE_TFTP_BLOCKSIZE("b:"),
			&local_file, &remote_file
			USE_FEATURE_TFTP_BLOCKSIZE(, &blocksize));
	argv += optind;

	flags = O_RDONLY;
	if (CMD_GET(cmd))
		flags = O_WRONLY | O_CREAT | O_TRUNC;

#if ENABLE_FEATURE_TFTP_BLOCKSIZE
	if (!tftp_blocksize_check(blocksize, 0))
		return EXIT_FAILURE;
#endif

	if (!local_file)
		local_file = remote_file;
	if (!remote_file)
		remote_file = local_file;
	/* Error if filename or host is not known */
	if (!remote_file || !argv[0])
		bb_show_usage();

	local_fd = CMD_GET(cmd) ? STDOUT_FILENO : STDIN_FILENO;
	if (!LONE_DASH(local_file)) {
		local_fd = xopen(local_file, flags);
	}

	port = bb_lookup_port(argv[1], "udp", 69);
	peer_lsa = xhost2sockaddr(argv[0], port);

#if ENABLE_DEBUG_TFTP
	fprintf(stderr, "using server '%s', remote_file '%s', local_file '%s'\n",
			xmalloc_sockaddr2dotted(&peer_lsa->u.sa),
			remote_file, local_file);
#endif

	result = tftp_protocol(
			USE_GETPUT(cmd,)
			NULL /* our_lsa*/,
			peer_lsa,
			remote_file, local_fd, blocksize);

	if (ENABLE_FEATURE_CLEAN_UP)
		close(local_fd);
	if (result != EXIT_SUCCESS && !LONE_DASH(local_file) && CMD_GET(cmd)) {
		unlink(local_file);
	}
	return result;
}

#endif /* ENABLE_TFTP */

#if ENABLE_TFTPD

/* TODO: libbb candidate? */
static len_and_sockaddr *get_sock_lsa(int s)
{
	len_and_sockaddr *lsa;
	socklen_t len = 0;

	if (getsockname(s, NULL, &len) != 0)
		return NULL;
	lsa = xzalloc(LSA_LEN_SIZE + len);
	lsa->len = len;
	getsockname(s, &lsa->u.sa, &lsa->len);
	return lsa;
}

int tftpd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int tftpd_main(int argc ATTRIBUTE_UNUSED, char **argv ATTRIBUTE_UNUSED)
{
	struct stat statbuf;
	char block_buf[TFTP_BLOCKSIZE_DEFAULT];
	len_and_sockaddr *our_lsa;
	len_and_sockaddr *peer_lsa;
	char *filename, *mode, *opt_str;
	int result, opcode, cmd, req_modebits, open_mode, local_fd, blksize;

	our_lsa = get_sock_lsa(STDIN_FILENO);
	if (!our_lsa)
		bb_perror_msg_and_die("stdin is not a socket");
	peer_lsa = xzalloc(LSA_LEN_SIZE + our_lsa->len);
	peer_lsa->len = our_lsa->len;

	if (argv[1])
		xchdir(argv[1]);

	result = recv_from_to(STDIN_FILENO, block_buf, sizeof(block_buf),
			0 /* flags */,
			&peer_lsa->u.sa, &our_lsa->u.sa, our_lsa->len);

	opcode = ntohs(*(uint16_t*)block_buf);
	if (result < 4 || result >= sizeof(block_buf)
	 || block_buf[result-1] != '\0'
	 || (opcode != TFTP_RRQ && opcode != TFTP_WRQ)
	) {
		bb_error_msg_and_die("malformed packet");
	}
	filename = block_buf + 2;
	if (filename[0] == '.' || strstr(filename, "/.")) {
		bb_error_msg_and_die("dot in filename");
	}
	mode = filename + strlen(filename) + 1;
	if (mode >= block_buf + sizeof(block_buf)
	 || strcmp(mode, "octet") != 0
	) {
		bb_error_msg_and_die("malformed packet");
	}
	blksize = TFTP_BLOCKSIZE_DEFAULT;
#if ENABLE_FEATURE_TFTP_BLOCKSIZE
	opt_str = mode + 6;
	if (opt_str < block_buf + sizeof(block_buf)) {
		char *res = tftp_option_get(opt_str, block_buf + sizeof(block_buf) - opt_str, "blksize");
		if (res) {
			int sz = xatoi_u(res);
			if (tftp_blocksize_check(sz, 0))
				blksize = sz;
		}
	}
#endif
	xstat(filename, &statbuf);
	/* if opcode == TFTP_WRQ: */
	cmd = 1; /* CMD_GET: we will receive file's data */
	req_modebits = 0222; /* writable by anyone */
	open_mode = O_WRONLY | O_TRUNC;
	if (opcode == TFTP_RRQ) {
		cmd = 2; /* CMD_PUT */
		req_modebits = 0444; /* readable by anyone */
		open_mode = O_RDONLY;
	}
	if (!S_ISREG(statbuf.st_mode)
	 || (statbuf.st_mode & req_modebits) != req_modebits
	) {
		bb_error_msg_and_die("access to '%s' is denied", filename);
	}
	local_fd = xopen(filename, open_mode);

	close(STDIN_FILENO); /* close old, possibly wildcard socket */
	/* tftp_protocol() will create new one, bound to particular local IP */
	result = tftp_protocol(
		USE_GETPUT(cmd,)
		our_lsa, peer_lsa,
		USE_TFTP(NULL /*remote_file*/,)
		local_fd,
		blksize
	);

	return result;
}

#endif /* ENABLE_TFTPD */

#endif /* ENABLE_FEATURE_TFTP_GET || ENABLE_FEATURE_TFTP_PUT */