X-Git-Url: https://git.librecmc.org/?a=blobdiff_plain;f=networking%2Ftelnetd.c;h=f06e9583e4f8900ece4f388d11f51f3316b98607;hb=179e88bec91cfe58096900dc5509a080ff37b083;hp=549488507127e2c1cb04858729df8444c6f04fd5;hpb=75f8d080a28f2a9076a5f60afeba41ac876a78a4;p=oweals%2Fbusybox.git diff --git a/networking/telnetd.c b/networking/telnetd.c index 549488507..f06e9583e 100644 --- a/networking/telnetd.c +++ b/networking/telnetd.c @@ -3,7 +3,7 @@ * Simple telnet server * Bjorn Wesen, Axis Communications AB (bjornw@axis.com) * - * Licensed under GPLv2 or later, see file LICENSE in this tarball for details. + * Licensed under GPLv2 or later, see file LICENSE in this source tree. * * --------------------------------------------------------------------------- * (C) Copyright 2000, Axis Communications AB, LUND, SWEDEN @@ -11,311 +11,548 @@ * * The telnetd manpage says it all: * - * Telnetd operates by allocating a pseudo-terminal device (see pty(4)) for - * a client, then creating a login process which has the slave side of the - * pseudo-terminal as stdin, stdout, and stderr. Telnetd manipulates the - * master side of the pseudo-terminal, implementing the telnet protocol and - * passing characters between the remote client and the login process. + * Telnetd operates by allocating a pseudo-terminal device (see pty(4)) for + * a client, then creating a login process which has the slave side of the + * pseudo-terminal as stdin, stdout, and stderr. Telnetd manipulates the + * master side of the pseudo-terminal, implementing the telnet protocol and + * passing characters between the remote client and the login process. * * Vladimir Oleynik 2001 - * Set process group corrections, initial busybox port + * Set process group corrections, initial busybox port */ +//config:config TELNETD +//config: bool "telnetd" +//config: default y +//config: select FEATURE_SYSLOG +//config: help +//config: A daemon for the TELNET protocol, allowing you to log onto the host +//config: running the daemon. Please keep in mind that the TELNET protocol +//config: sends passwords in plain text. If you can't afford the space for an +//config: SSH daemon and you trust your network, you may say 'y' here. As a +//config: more secure alternative, you should seriously consider installing the +//config: very small Dropbear SSH daemon instead: +//config: http://matt.ucc.asn.au/dropbear/dropbear.html +//config: +//config: Note that for busybox telnetd to work you need several things: +//config: First of all, your kernel needs: +//config: CONFIG_UNIX98_PTYS=y +//config: +//config: Next, you need a /dev/pts directory on your root filesystem: +//config: +//config: $ ls -ld /dev/pts +//config: drwxr-xr-x 2 root root 0 Sep 23 13:21 /dev/pts/ +//config: +//config: Next you need the pseudo terminal master multiplexer /dev/ptmx: +//config: +//config: $ ls -la /dev/ptmx +//config: crw-rw-rw- 1 root tty 5, 2 Sep 23 13:55 /dev/ptmx +//config: +//config: Any /dev/ttyp[0-9]* files you may have can be removed. +//config: Next, you need to mount the devpts filesystem on /dev/pts using: +//config: +//config: mount -t devpts devpts /dev/pts +//config: +//config: You need to be sure that busybox has LOGIN and +//config: FEATURE_SUID enabled. And finally, you should make +//config: certain that Busybox has been installed setuid root: +//config: +//config: chown root.root /bin/busybox +//config: chmod 4755 /bin/busybox +//config: +//config: with all that done, telnetd _should_ work.... +//config: +//config:config FEATURE_TELNETD_STANDALONE +//config: bool "Support standalone telnetd (not inetd only)" +//config: default y +//config: depends on TELNETD +//config: help +//config: Selecting this will make telnetd able to run standalone. +//config: +//config:config FEATURE_TELNETD_INETD_WAIT +//config: bool "Support -w SEC option (inetd wait mode)" +//config: default y +//config: depends on FEATURE_TELNETD_STANDALONE +//config: help +//config: This option allows you to run telnetd in "inet wait" mode. +//config: Example inetd.conf line (note "wait", not usual "nowait"): +//config: +//config: telnet stream tcp wait root /bin/telnetd telnetd -w10 +//config: +//config: In this example, inetd passes _listening_ socket_ as fd 0 +//config: to telnetd when connection appears. +//config: telnetd will wait for connections until all existing +//config: connections are closed, and no new connections +//config: appear during 10 seconds. Then it exits, and inetd continues +//config: to listen for new connections. +//config: +//config: This option is rarely used. "tcp nowait" is much more usual +//config: way of running tcp services, including telnetd. +//config: You most probably want to say N here. + +//applet:IF_TELNETD(APPLET(telnetd, BB_DIR_USR_SBIN, BB_SUID_DROP)) + +//kbuild:lib-$(CONFIG_TELNETD) += telnetd.o + +//usage:#define telnetd_trivial_usage +//usage: "[OPTIONS]" +//usage:#define telnetd_full_usage "\n\n" +//usage: "Handle incoming telnet connections" +//usage: IF_NOT_FEATURE_TELNETD_STANDALONE(" via inetd") "\n" +//usage: "\n -l LOGIN Exec LOGIN on connect" +//usage: "\n -f ISSUE_FILE Display ISSUE_FILE instead of /etc/issue" +//usage: "\n -K Close connection as soon as login exits" +//usage: "\n (normally wait until all programs close slave pty)" +//usage: IF_FEATURE_TELNETD_STANDALONE( +//usage: "\n -p PORT Port to listen on" +//usage: "\n -b ADDR[:PORT] Address to bind to" +//usage: "\n -F Run in foreground" +//usage: "\n -i Inetd mode" +//usage: IF_FEATURE_TELNETD_INETD_WAIT( +//usage: "\n -w SEC Inetd 'wait' mode, linger time SEC" +//usage: "\n -S Log to syslog (implied by -i or without -F and -w)" +//usage: ) +//usage: ) -/*#define DEBUG 1 */ #define DEBUG 0 -#include "busybox.h" +#include "libbb.h" +#include "common_bufsiz.h" +#include #if DEBUG -#define TELCMDS -#define TELOPTS +# define TELCMDS +# define TELOPTS #endif #include -#include -#define BUFSIZE 4000 - -#if ENABLE_FEATURE_IPV6 -#define SOCKET_TYPE AF_INET6 -typedef struct sockaddr_in6 sockaddr_type; -#else -#define SOCKET_TYPE AF_INET -typedef struct sockaddr_in sockaddr_type; -#endif - -#if ENABLE_LOGIN -static const char *loginpath = "/bin/login"; -#else -static const char *loginpath = DEFAULT_SHELL; -#endif - -static const char *issuefile = "/etc/issue.net"; - -/* shell name and arguments */ - -static const char *argv_init[2]; - -/* structure that describes a session */ - struct tsession { struct tsession *next; - int sockfd_read, sockfd_write, ptyfd; - int shell_pid; + pid_t shell_pid; + int sockfd_read; + int sockfd_write; + int ptyfd; + smallint buffered_IAC_for_pty; + /* two circular buffers */ - char *buf1, *buf2; + /*char *buf1, *buf2;*/ +/*#define TS_BUF1(ts) ts->buf1*/ +/*#define TS_BUF2(ts) TS_BUF2(ts)*/ +#define TS_BUF1(ts) ((unsigned char*)(ts + 1)) +#define TS_BUF2(ts) (((unsigned char*)(ts + 1)) + BUFSIZE) int rdidx1, wridx1, size1; int rdidx2, wridx2, size2; }; -/* - This is how the buffers are used. The arrows indicate the movement - of data. - - +-------+ wridx1++ +------+ rdidx1++ +----------+ - | | <-------------- | buf1 | <-------------- | | - | | size1-- +------+ size1++ | | - | pty | | socket | - | | rdidx2++ +------+ wridx2++ | | - | | --------------> | buf2 | --------------> | | - +-------+ size2++ +------+ size2-- +----------+ - - Each session has got two buffers. -*/ - -static int maxfd; - -static struct tsession *sessions; - - -/* - Remove all IAC's from the buffer pointed to by bf (received IACs are ignored - and must be removed so as to not be interpreted by the terminal). Make an - uninterrupted string of characters fit for the terminal. Do this by packing - all characters meant for the terminal sequentially towards the end of bf. - - Return a pointer to the beginning of the characters meant for the terminal. - and make *num_totty the number of characters that should be sent to - the terminal. - - Note - If an IAC (3 byte quantity) starts before (bf + len) but extends - past (bf + len) then that IAC will be left unprocessed and *processed will be - less than len. - - FIXME - if we mean to send 0xFF to the terminal then it will be escaped, - what is the escape character? We aren't handling that situation here. - - CR-LF ->'s CR mapping is also done here, for convenience +/* Two buffers are directly after tsession in malloced memory. + * Make whole thing fit in 4k */ +enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 }; + + +/* Globals */ +struct globals { + struct tsession *sessions; + const char *loginpath; + const char *issuefile; + int maxfd; +} FIX_ALIASING; +#define G (*(struct globals*)bb_common_bufsiz1) +#define INIT_G() do { \ + setup_common_bufsiz(); \ + G.loginpath = "/bin/login"; \ + G.issuefile = "/etc/issue.net"; \ +} while (0) + + +/* Write some buf1 data to pty, processing IACs. + * Update wridx1 and size1. Return < 0 on error. + * Buggy if IAC is present but incomplete: skips them. */ -static char * -remove_iacs(struct tsession *ts, int *pnum_totty) +static ssize_t +safe_write_to_pty_decode_iac(struct tsession *ts) { - unsigned char *ptr0 = (unsigned char *)ts->buf1 + ts->wridx1; - unsigned char *ptr = ptr0; - unsigned char *totty = ptr; - unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1); - int processed; - int num_totty; - - while (ptr < end) { - if (*ptr != IAC) { - int c = *ptr; - *totty++ = *ptr++; - /* We now map \r\n ==> \r for pragmatic reasons. - * Many client implementations send \r\n when - * the user hits the CarriageReturn key. - */ - if (c == '\r' && (*ptr == '\n' || *ptr == 0) && ptr < end) - ptr++; - } else { - /* - * TELOPT_NAWS support! - */ - if ((ptr+2) >= end) { - /* only the beginning of the IAC is in the - buffer we were asked to process, we can't - process this char. */ - break; - } + unsigned wr; + ssize_t rc; + unsigned char *buf; + unsigned char *found; + + buf = TS_BUF1(ts) + ts->wridx1; + wr = MIN(BUFSIZE - ts->wridx1, ts->size1); + /* wr is at least 1 here */ + + if (ts->buffered_IAC_for_pty) { + /* Last time we stopped on a "dangling" IAC byte. + * We removed it from the buffer back then. + * Now pretend it's still there, and jump to IAC processing. + */ + ts->buffered_IAC_for_pty = 0; + wr++; + ts->size1++; + buf--; /* Yes, this can point before the buffer. It's ok */ + ts->wridx1--; + goto handle_iac; + } - /* - * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE - */ - else if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) { - struct winsize ws; - if ((ptr+8) >= end) - break; /* incomplete, can't process */ - ws.ws_col = (ptr[3] << 8) | ptr[4]; - ws.ws_row = (ptr[5] << 8) | ptr[6]; - ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws); - ptr += 9; - } else { - /* skip 3-byte IAC non-SB cmd */ -#if DEBUG - fprintf(stderr, "Ignoring IAC %s,%s\n", - TELCMD(ptr[1]), TELOPT(ptr[2])); -#endif - ptr += 3; - } + found = memchr(buf, IAC, wr); + if (found != buf) { + /* There is a "prefix" of non-IAC chars. + * Write only them, and return. + */ + if (found) + wr = found - buf; + + /* We map \r\n ==> \r for pragmatic reasons: + * many client implementations send \r\n when + * the user hits the CarriageReturn key. + * See RFC 1123 3.3.1 Telnet End-of-Line Convention. + */ + rc = wr; + found = memchr(buf, '\r', wr); + if (found) + rc = found - buf + 1; + rc = safe_write(ts->ptyfd, buf, rc); + if (rc <= 0) + return rc; + if (rc < wr /* don't look past available data */ + && buf[rc-1] == '\r' /* need this: imagine that write was _short_ */ + && (buf[rc] == '\n' || buf[rc] == '\0') + ) { + rc++; } + goto update_and_return; } - processed = ptr - ptr0; - num_totty = totty - ptr0; - /* the difference between processed and num_to tty - is all the iacs we removed from the stream. - Adjust buf1 accordingly. */ - ts->wridx1 += processed - num_totty; - ts->size1 -= processed - num_totty; - *pnum_totty = num_totty; - /* move the chars meant for the terminal towards the end of the - buffer. */ - return memmove(ptr - num_totty, ptr0, num_totty); -} - + /* buf starts with IAC char. Process that sequence. + * Example: we get this from our own (bbox) telnet client: + * read(5, "\377\374\1""\377\373\37""\377\372\37\0\262\0@\377\360""\377\375\1""\377\375\3"): + * IAC WONT ECHO, IAC WILL NAWS, IAC SB NAWS IAC SE, IAC DO SGA + * Another example (telnet-0.17 from old-netkit): + * read(4, "\377\375\3""\377\373\30""\377\373\37""\377\373 ""\377\373!""\377\373\"""\377\373'" + * "\377\375\5""\377\373#""\377\374\1""\377\372\37\0\257\0I\377\360""\377\375\1"): + * IAC DO SGA, IAC WILL TTYPE, IAC WILL NAWS, IAC WILL TSPEED, IAC WILL LFLOW, IAC WILL LINEMODE, IAC WILL NEW_ENVIRON, + * IAC DO STATUS, IAC WILL XDISPLOC, IAC WONT ECHO, IAC SB NAWS IAC SE, IAC DO ECHO + */ + if (wr <= 1) { + /* Only the single IAC byte is in the buffer, eat it + * and set a flag "process the rest of the sequence + * next time we are here". + */ + //bb_error_msg("dangling IAC!"); + ts->buffered_IAC_for_pty = 1; + rc = 1; + goto update_and_return; + } -static int -getpty(char *line, int size) -{ - int p; -#if ENABLE_FEATURE_DEVPTS - p = open("/dev/ptmx", O_RDWR); - if (p > 0) { - const char *name; - grantpt(p); - unlockpt(p); - name = ptsname(p); - if (!name) { - bb_perror_msg("ptsname error (is /dev/pts mounted?)"); - return -1; - } - safe_strncpy(line, name, size); - return p; + handle_iac: + /* 2-byte commands (240..250 and 255): + * IAC IAC (255) Literal 255. Supported. + * IAC SE (240) End of subnegotiation. Treated as NOP. + * IAC NOP (241) NOP. Supported. + * IAC BRK (243) Break. Like serial line break. TODO via tcsendbreak()? + * IAC AYT (246) Are you there. Send back evidence that AYT was seen. TODO (send NOP back)? + * These don't look useful: + * IAC DM (242) Data mark. What is this? + * IAC IP (244) Suspend, interrupt or abort the process. (Ancient cousin of ^C). + * IAC AO (245) Abort output. "You can continue running, but do not send me the output". + * IAC EC (247) Erase character. The receiver should delete the last received char. + * IAC EL (248) Erase line. The receiver should delete everything up tp last newline. + * IAC GA (249) Go ahead. For half-duplex lines: "now you talk". + * Implemented only as part of NAWS: + * IAC SB (250) Subnegotiation of an option follows. + */ + if (buf[1] == IAC) { + /* Literal 255 (emacs M-DEL) */ + //bb_error_msg("255!"); + rc = safe_write(ts->ptyfd, &buf[1], 1); + /* + * If we went through buffered_IAC_for_pty==1 path, + * bailing out on error like below messes up the buffer. + * EAGAIN is highly unlikely here, other errors will be + * repeated on next write, let's just skip error check. + */ +#if 0 + if (rc <= 0) + return rc; +#endif + rc = 2; + goto update_and_return; + } + if (buf[1] >= 240 && buf[1] <= 249) { + /* NOP (241). Ignore (putty keepalive, etc) */ + /* All other 2-byte commands also treated as NOPs here */ + rc = 2; + goto update_and_return; } -#else - struct stat stb; - int i; - int j; - strcpy(line, "/dev/ptyXX"); + if (wr <= 2) { +/* BUG: only 2 bytes of the IAC is in the buffer, we just eat them. + * This is not a practical problem since >2 byte IACs are seen only + * in initial negotiation, when buffer is empty + */ + rc = 2; + goto update_and_return; + } - for (i = 0; i < 16; i++) { - line[8] = "pqrstuvwxyzabcde"[i]; - line[9] = '0'; - if (stat(line, &stb) < 0) { - continue; - } - for (j = 0; j < 16; j++) { - line[9] = j < 10 ? j + '0' : j - 10 + 'a'; - if (DEBUG) - fprintf(stderr, "Trying to open device: %s\n", line); - p = open(line, O_RDWR | O_NOCTTY); - if (p >= 0) { - line[5] = 't'; - return p; + if (buf[1] == SB) { + if (buf[2] == TELOPT_NAWS) { + /* IAC SB, TELOPT_NAWS, 4-byte, IAC SE */ + struct winsize ws; + if (wr <= 6) { +/* BUG: incomplete, can't process */ + rc = wr; + goto update_and_return; } + memset(&ws, 0, sizeof(ws)); /* pixel sizes are set to 0 */ + ws.ws_col = (buf[3] << 8) | buf[4]; + ws.ws_row = (buf[5] << 8) | buf[6]; + ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws); + rc = 7; + /* trailing IAC SE will be eaten separately, as 2-byte NOP */ + goto update_and_return; } + /* else: other subnegs not supported yet */ } -#endif /* FEATURE_DEVPTS */ - return -1; -} + /* Assume it is a 3-byte WILL/WONT/DO/DONT 251..254 command and skip it */ +#if DEBUG + fprintf(stderr, "Ignoring IAC %s,%s\n", + TELCMD(buf[1]), TELOPT(buf[2])); +#endif + rc = 3; + + update_and_return: + ts->wridx1 += rc; + if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */ + ts->wridx1 = 0; + ts->size1 -= rc; + /* + * Hack. We cannot process IACs which wrap around buffer's end. + * Since properly fixing it requires writing bigger code, + * we rely instead on this code making it virtually impossible + * to have wrapped IAC (people don't type at 2k/second). + * It also allows for bigger reads in common case. + */ + if (ts->size1 == 0) { /* very typical */ + //bb_error_msg("zero size1"); + ts->rdidx1 = 0; + ts->wridx1 = 0; + return rc; + } + wr = ts->wridx1; + if (wr != 0 && wr < ts->rdidx1) { + /* Buffer is not wrapped yet. + * We can easily move it to the beginning. + */ + //bb_error_msg("moved %d", wr); + memmove(TS_BUF1(ts), TS_BUF1(ts) + wr, ts->size1); + ts->rdidx1 -= wr; + ts->wridx1 = 0; + } + return rc; +} -static void -send_iac(struct tsession *ts, unsigned char command, int option) +/* + * Converting single IAC into double on output + */ +static size_t safe_write_double_iac(int fd, const char *buf, size_t count) { - /* We rely on that there is space in the buffer for now. */ - char *b = ts->buf2 + ts->rdidx2; - *b++ = IAC; - *b++ = command; - *b++ = option; - ts->rdidx2 += 3; - ts->size2 += 3; + const char *IACptr; + size_t wr, rc, total; + + total = 0; + while (1) { + if (count == 0) + return total; + if (*buf == (char)IAC) { + static const char IACIAC[] ALIGN1 = { IAC, IAC }; + rc = safe_write(fd, IACIAC, 2); +/* BUG: if partial write was only 1 byte long, we end up emitting just one IAC */ + if (rc != 2) + break; + buf++; + total++; + count--; + continue; + } + /* count != 0, *buf != IAC */ + IACptr = memchr(buf, IAC, count); + wr = count; + if (IACptr) + wr = IACptr - buf; + rc = safe_write(fd, buf, wr); + if (rc != wr) + break; + buf += rc; + total += rc; + count -= rc; + } + /* here: rc - result of last short write */ + if ((ssize_t)rc < 0) { /* error? */ + if (total == 0) + return rc; + rc = 0; + } + return total + rc; } +/* Must match getopt32 string */ +enum { + OPT_WATCHCHILD = (1 << 2), /* -K */ + OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */ + OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p PORT */ + OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */ + OPT_SYSLOG = (1 << 7) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -S */ + OPT_WAIT = (1 << 8) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -w SEC */ +}; static struct tsession * make_new_session( - USE_FEATURE_TELNETD_STANDALONE(int sock_r, int sock_w) - SKIP_FEATURE_TELNETD_STANDALONE(void) + IF_FEATURE_TELNETD_STANDALONE(int sock) + IF_NOT_FEATURE_TELNETD_STANDALONE(void) ) { +#if !ENABLE_FEATURE_TELNETD_STANDALONE + enum { sock = 0 }; +#endif + const char *login_argv[2]; struct termios termbuf; int fd, pid; - char tty_name[32]; + char tty_name[GETPTY_BUFSIZE]; struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2); - ts->buf1 = (char *)(&ts[1]); - ts->buf2 = ts->buf1 + BUFSIZE; + /*ts->buf1 = (char *)(ts + 1);*/ + /*ts->buf2 = ts->buf1 + BUFSIZE;*/ - /* Got a new connection, set up a tty. */ - fd = getpty(tty_name, 32); - if (fd < 0) { - bb_error_msg("all terminals in use"); - return NULL; - } - if (fd > maxfd) maxfd = fd; - ndelay_on(ts->ptyfd = fd); + /* Got a new connection, set up a tty */ + fd = xgetpty(tty_name); + if (fd > G.maxfd) + G.maxfd = fd; + ts->ptyfd = fd; + ndelay_on(fd); + close_on_exec_on(fd); + + /* SO_KEEPALIVE by popular demand */ + setsockopt_keepalive(sock); #if ENABLE_FEATURE_TELNETD_STANDALONE - if (sock_w > maxfd) maxfd = sock_w; - if (sock_r > maxfd) maxfd = sock_r; - ndelay_on(ts->sockfd_write = sock_w); - ndelay_on(ts->sockfd_read = sock_r); + ts->sockfd_read = sock; + ndelay_on(sock); + if (sock == 0) { /* We are called with fd 0 - we are in inetd mode */ + sock++; /* so use fd 1 for output */ + ndelay_on(sock); + } + ts->sockfd_write = sock; + if (sock > G.maxfd) + G.maxfd = sock; #else + /* ts->sockfd_read = 0; - done by xzalloc */ ts->sockfd_write = 1; - /* xzalloc: ts->sockfd_read = 0; */ ndelay_on(0); ndelay_on(1); #endif + /* Make the telnet client understand we will echo characters so it * should not do it locally. We don't tell the client to run linemode, * because we want to handle line editing and tab completion and other * stuff that requires char-by-char support. */ - send_iac(ts, DO, TELOPT_ECHO); - send_iac(ts, DO, TELOPT_NAWS); - send_iac(ts, DO, TELOPT_LFLOW); - send_iac(ts, WILL, TELOPT_ECHO); - send_iac(ts, WILL, TELOPT_SGA); + { + static const char iacs_to_send[] ALIGN1 = { + IAC, DO, TELOPT_ECHO, + IAC, DO, TELOPT_NAWS, + /* This requires telnetd.ctrlSQ.patch (incomplete) */ + /*IAC, DO, TELOPT_LFLOW,*/ + IAC, WILL, TELOPT_ECHO, + IAC, WILL, TELOPT_SGA + }; + /* This confuses safe_write_double_iac(), it will try to duplicate + * each IAC... */ + //memcpy(TS_BUF2(ts), iacs_to_send, sizeof(iacs_to_send)); + //ts->rdidx2 = sizeof(iacs_to_send); + //ts->size2 = sizeof(iacs_to_send); + /* So just stuff it into TCP stream! (no error check...) */ +#if ENABLE_FEATURE_TELNETD_STANDALONE + safe_write(sock, iacs_to_send, sizeof(iacs_to_send)); +#else + safe_write(1, iacs_to_send, sizeof(iacs_to_send)); +#endif + /*ts->rdidx2 = 0; - xzalloc did it */ + /*ts->size2 = 0;*/ + } - pid = fork(); + fflush_all(); + pid = vfork(); /* NOMMU-friendly */ if (pid < 0) { free(ts); close(fd); - bb_perror_msg("fork"); + /* sock will be closed by caller */ + bb_perror_msg("vfork"); return NULL; } if (pid > 0) { - /* parent */ + /* Parent */ ts->shell_pid = pid; return ts; } - - /* child */ - - /* open the child's side of the tty. */ - fd = xopen(tty_name, O_RDWR /*| O_NOCTTY*/); - dup2(fd, 0); - dup2(fd, 1); - dup2(fd, 2); - while (fd > 2) close(fd--); - /* make new process group */ + + /* Child */ + /* Careful - we are after vfork! */ + + /* Restore default signal handling ASAP */ + bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL); + + pid = getpid(); + + if (ENABLE_FEATURE_UTMP) { + len_and_sockaddr *lsa = get_peer_lsa(sock); + char *hostname = NULL; + if (lsa) { + hostname = xmalloc_sockaddr2dotted(&lsa->u.sa); + free(lsa); + } + write_new_utmp(pid, LOGIN_PROCESS, tty_name, /*username:*/ "LOGIN", hostname); + free(hostname); + } + + /* Make new session and process group */ setsid(); - tcsetpgrp(0, getpid()); - /* The pseudo-terminal allocated to the client is configured to operate in - * cooked mode, and with XTABS CRMOD enabled (see tty(4)). */ + /* Open the child's side of the tty */ + /* NB: setsid() disconnects from any previous ctty's. Therefore + * we must open child's side of the tty AFTER setsid! */ + close(0); + xopen(tty_name, O_RDWR); /* becomes our ctty */ + xdup2(0, 1); + xdup2(0, 2); + tcsetpgrp(0, pid); /* switch this tty's process group to us */ + + /* The pseudo-terminal allocated to the client is configured to operate + * in cooked mode, and with XTABS CRMOD enabled (see tty(4)) */ tcgetattr(0, &termbuf); termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */ - termbuf.c_oflag |= ONLCR|XTABS; + termbuf.c_oflag |= ONLCR | XTABS; termbuf.c_iflag |= ICRNL; termbuf.c_iflag &= ~IXOFF; /*termbuf.c_lflag &= ~ICANON;*/ - tcsetattr(0, TCSANOW, &termbuf); - - print_login_issue(issuefile, NULL); - - /* exec shell, with correct argv and env */ - execv(loginpath, (char *const *)argv_init); - bb_perror_msg_and_die("execv"); + tcsetattr_stdin_TCSANOW(&termbuf); + + /* Uses FILE-based I/O to stdout, but does fflush_all(), + * so should be safe with vfork. + * I fear, though, that some users will have ridiculously big + * issue files, and they may block writing to fd 1, + * (parent is supposed to read it, but parent waits + * for vforked child to exec!) */ + print_login_issue(G.issuefile, tty_name); + + /* Exec shell / login / whatever */ + login_argv[0] = G.loginpath; + login_argv[1] = NULL; + /* exec busybox applet (if PREFER_APPLETS=y), if that fails, + * exec external program. + * NB: sock is either 0 or has CLOEXEC set on it. + * fd has CLOEXEC set on it too. These two fds will be closed here. + */ + BB_EXECVP(G.loginpath, (char **)login_argv); + /* _exit is safer with vfork, and we shouldn't send message + * to remote clients anyway */ + _exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", G.loginpath);*/ } #if ENABLE_FEATURE_TELNETD_STANDALONE @@ -323,288 +560,330 @@ make_new_session( static void free_session(struct tsession *ts) { - struct tsession *t = sessions; + struct tsession *t; - /* unlink this telnet session from the session list */ + if (option_mask32 & OPT_INETD) + exit(EXIT_SUCCESS); + + /* Unlink this telnet session from the session list */ + t = G.sessions; if (t == ts) - sessions = ts->next; + G.sessions = ts->next; else { while (t->next != ts) t = t->next; t->next = ts->next; } +#if 0 + /* It was said that "normal" telnetd just closes ptyfd, + * doesn't send SIGKILL. When we close ptyfd, + * kernel sends SIGHUP to processes having slave side opened. */ kill(ts->shell_pid, SIGKILL); - wait4(ts->shell_pid, NULL, 0, NULL); + waitpid(ts->shell_pid, NULL, 0); +#endif close(ts->ptyfd); close(ts->sockfd_read); - /* error if ts->sockfd_read == ts->sockfd_write. So what? ;) */ - close(ts->sockfd_write); + /* We do not need to close(ts->sockfd_write), it's the same + * as sockfd_read unless we are in inetd mode. But in inetd mode + * we do not reach this */ free(ts); - /* scan all sessions and find new maxfd */ - ts = sessions; - maxfd = 0; + /* Scan all sessions and find new maxfd */ + G.maxfd = 0; + ts = G.sessions; while (ts) { - if (maxfd < ts->ptyfd) - maxfd = ts->ptyfd; - if (maxfd < ts->sockfd_read) - maxfd = ts->sockfd_read; - if (maxfd < ts->sockfd_write) - maxfd = ts->sockfd_write; + if (G.maxfd < ts->ptyfd) + G.maxfd = ts->ptyfd; + if (G.maxfd < ts->sockfd_read) + G.maxfd = ts->sockfd_read; +#if 0 + /* Again, sockfd_write == sockfd_read here */ + if (G.maxfd < ts->sockfd_write) + G.maxfd = ts->sockfd_write; +#endif ts = ts->next; } } -static int -create_socket(int port, const char *opt_bindaddr) -{ - static const int on = 1; - int fd; - sockaddr_type sa; -#if !ENABLE_FEATURE_IPV6 - struct in_addr bind_addr = { .s_addr = 0x0 }; - - /* TODO: generic string -> sockaddr converter */ - if (opt_bindaddr && inet_aton(opt_bindaddr, &bind_addr) == 0) - bb_show_usage(); -#endif - fd = xsocket(SOCKET_TYPE, SOCK_STREAM, 0); - setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)); - memset((void *)&sa, 0, sizeof(sa)); -#if ENABLE_FEATURE_IPV6 - sa.sin6_family = AF_INET6; - sa.sin6_port = htons(port); - /* sa.sin6_addr = bind_addr6; */ -#else - sa.sin_family = AF_INET; - sa.sin_port = htons(port); - sa.sin_addr = bind_addr; -#endif - xbind(fd, (struct sockaddr *) &sa, sizeof(sa)); - xlisten(fd, 1); - return fd; -} - #else /* !FEATURE_TELNETD_STANDALONE */ -/* Never actually called */ -void free_session(struct tsession *ts); -int create_socket(int port, const char *opt_bindaddr); +/* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */ +#define free_session(ts) return 0 #endif +static void handle_sigchld(int sig UNUSED_PARAM) +{ + pid_t pid; + struct tsession *ts; + int save_errno = errno; + + /* Looping: more than one child may have exited */ + while (1) { + pid = wait_any_nohang(NULL); + if (pid <= 0) + break; + ts = G.sessions; + while (ts) { + if (ts->shell_pid == pid) { + ts->shell_pid = -1; + update_utmp_DEAD_PROCESS(pid); + break; + } + ts = ts->next; + } + } + + errno = save_errno; +} -int -telnetd_main(int argc, char **argv) +int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; +int telnetd_main(int argc UNUSED_PARAM, char **argv) { fd_set rdfdset, wrfdset; unsigned opt; - int selret, maxlen, w, r; + int count; struct tsession *ts; #if ENABLE_FEATURE_TELNETD_STANDALONE #define IS_INETD (opt & OPT_INETD) - int master_fd = -1; /* be happy, gcc */ - unsigned portnbr = 23; + int master_fd = master_fd; /* for compiler */ + int sec_linger = sec_linger; char *opt_bindaddr = NULL; char *opt_portnbr; #else enum { IS_INETD = 1, master_fd = -1, - portnbr = 23, }; #endif - enum { - OPT_PORT = 4 * ENABLE_FEATURE_TELNETD_STANDALONE, - OPT_FOREGROUND = 0x10 * ENABLE_FEATURE_TELNETD_STANDALONE, - OPT_INETD = 0x20 * ENABLE_FEATURE_TELNETD_STANDALONE, - }; - - opt = getopt32(argc, argv, "f:l:" USE_FEATURE_TELNETD_STANDALONE("p:b:Fi"), - &issuefile, &loginpath - USE_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr)); + INIT_G(); + + /* -w NUM, and implies -F. -w and -i don't mix */ + IF_FEATURE_TELNETD_INETD_WAIT(opt_complementary = "wF:i--w:w--i";) + /* Even if !STANDALONE, we accept (and ignore) -i, thus people + * don't need to guess whether it's ok to pass -i to us */ + opt = getopt32(argv, "f:l:Ki" + IF_FEATURE_TELNETD_STANDALONE("p:b:F") + IF_FEATURE_TELNETD_INETD_WAIT("Sw:+"), + &G.issuefile, &G.loginpath + IF_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr) + IF_FEATURE_TELNETD_INETD_WAIT(, &sec_linger) + ); + if (!IS_INETD /*&& !re_execed*/) { + /* inform that we start in standalone mode? + * May be useful when people forget to give -i */ + /*bb_error_msg("listening for connections");*/ + if (!(opt & OPT_FOREGROUND)) { + /* DAEMON_CHDIR_ROOT was giving inconsistent + * behavior with/without -F, -i */ + bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv); + } + } /* Redirect log to syslog early, if needed */ - if (IS_INETD || !(opt & OPT_FOREGROUND)) { - openlog(applet_name, 0, LOG_USER); + if (IS_INETD || (opt & OPT_SYSLOG) || !(opt & OPT_FOREGROUND)) { + openlog(applet_name, LOG_PID, LOG_DAEMON); logmode = LOGMODE_SYSLOG; } - //if (opt & 1) // -f - //if (opt & 2) // -l - USE_FEATURE_TELNETD_STANDALONE( - if (opt & OPT_PORT) // -p - portnbr = xatou16(opt_portnbr); - //if (opt & 8) // -b - //if (opt & 0x10) // -F - //if (opt & 0x20) // -i - ); - - /* Used to check access(loginpath, X_OK) here. Pointless. - * exec will do this for us for free later. */ - argv_init[0] = loginpath; - #if ENABLE_FEATURE_TELNETD_STANDALONE if (IS_INETD) { - sessions = make_new_session(0, 1); + G.sessions = make_new_session(0); + if (!G.sessions) /* pty opening or vfork problem, exit */ + return 1; /* make_new_session printed error message */ } else { - master_fd = create_socket(portnbr, opt_bindaddr); - if (!(opt & OPT_FOREGROUND)) - xdaemon(0, 0); + master_fd = 0; + if (!(opt & OPT_WAIT)) { + unsigned portnbr = 23; + if (opt & OPT_PORT) + portnbr = xatou16(opt_portnbr); + master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr); + xlisten(master_fd, 1); + } + close_on_exec_on(master_fd); } #else - sessions = make_new_session(); + G.sessions = make_new_session(); + if (!G.sessions) /* pty opening or vfork problem, exit */ + return 1; /* make_new_session printed error message */ #endif /* We don't want to die if just one session is broken */ signal(SIGPIPE, SIG_IGN); + if (opt & OPT_WATCHCHILD) + signal(SIGCHLD, handle_sigchld); + else /* prevent dead children from becoming zombies */ + signal(SIGCHLD, SIG_IGN); + +/* + This is how the buffers are used. The arrows indicate data flow. + + +-------+ wridx1++ +------+ rdidx1++ +----------+ + | | <-------------- | buf1 | <-------------- | | + | | size1-- +------+ size1++ | | + | pty | | socket | + | | rdidx2++ +------+ wridx2++ | | + | | --------------> | buf2 | --------------> | | + +-------+ size2++ +------+ size2-- +----------+ + + size1: "how many bytes are buffered for pty between rdidx1 and wridx1?" + size2: "how many bytes are buffered for socket between rdidx2 and wridx2?" + + Each session has got two buffers. Buffers are circular. If sizeN == 0, + buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases + rdidxN == wridxN. +*/ again: FD_ZERO(&rdfdset); FD_ZERO(&wrfdset); + + /* Select on the master socket, all telnet sockets and their + * ptys if there is room in their session buffers. + * NB: scalability problem: we recalculate entire bitmap + * before each select. Can be a problem with 500+ connections. */ + ts = G.sessions; + while (ts) { + struct tsession *next = ts->next; /* in case we free ts */ + if (ts->shell_pid == -1) { + /* Child died and we detected that */ + free_session(ts); + } else { + if (ts->size1 > 0) /* can write to pty */ + FD_SET(ts->ptyfd, &wrfdset); + if (ts->size1 < BUFSIZE) /* can read from socket */ + FD_SET(ts->sockfd_read, &rdfdset); + if (ts->size2 > 0) /* can write to socket */ + FD_SET(ts->sockfd_write, &wrfdset); + if (ts->size2 < BUFSIZE) /* can read from pty */ + FD_SET(ts->ptyfd, &rdfdset); + } + ts = next; + } if (!IS_INETD) { FD_SET(master_fd, &rdfdset); /* This is needed because free_session() does not - * take into account master_fd when it finds new - * maxfd among remaining fd's: */ - if (master_fd > maxfd) - maxfd = master_fd; + * take master_fd into account when it finds new + * maxfd among remaining fd's */ + if (master_fd > G.maxfd) + G.maxfd = master_fd; } - /* select on the master socket, all telnet sockets and their - * ptys if there is room in their session buffers. */ - ts = sessions; - while (ts) { - /* buf1 is used from socket to pty - * buf2 is used from pty to socket */ - if (ts->size1 > 0) /* can write to pty */ - FD_SET(ts->ptyfd, &wrfdset); - if (ts->size1 < BUFSIZE) /* can read from socket */ - FD_SET(ts->sockfd_read, &rdfdset); - if (ts->size2 > 0) /* can write to socket */ - FD_SET(ts->sockfd_write, &wrfdset); - if (ts->size2 < BUFSIZE) /* can read from pty */ - FD_SET(ts->ptyfd, &rdfdset); - ts = ts->next; + { + struct timeval *tv_ptr = NULL; +#if ENABLE_FEATURE_TELNETD_INETD_WAIT + struct timeval tv; + if ((opt & OPT_WAIT) && !G.sessions) { + tv.tv_sec = sec_linger; + tv.tv_usec = 0; + tv_ptr = &tv; + } +#endif + count = select(G.maxfd + 1, &rdfdset, &wrfdset, NULL, tv_ptr); } - - selret = select(maxfd + 1, &rdfdset, &wrfdset, 0, 0); - if (!selret) + if (count == 0) /* "telnetd -w SEC" timed out */ return 0; + if (count < 0) + goto again; /* EINTR or ENOMEM */ #if ENABLE_FEATURE_TELNETD_STANDALONE - /* First check for and accept new sessions. */ + /* Check for and accept new sessions */ if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) { - sockaddr_type sa; int fd; - socklen_t salen; struct tsession *new_ts; - salen = sizeof(sa); - fd = accept(master_fd, (struct sockaddr *)&sa, &salen); + fd = accept(master_fd, NULL, NULL); if (fd < 0) goto again; - /* Create a new session and link it into our active list */ - new_ts = make_new_session(fd, fd); + close_on_exec_on(fd); + + /* Create a new session and link it into active list */ + new_ts = make_new_session(fd); if (new_ts) { - new_ts->next = sessions; - sessions = new_ts; + new_ts->next = G.sessions; + G.sessions = new_ts; } else { close(fd); } } #endif - /* Then check for data tunneling. */ - ts = sessions; + /* Then check for data tunneling */ + ts = G.sessions; while (ts) { /* For all sessions... */ - struct tsession *next = ts->next; /* in case we free ts. */ - - if (ts->size1 && FD_ISSET(ts->ptyfd, &wrfdset)) { - int num_totty; - char *ptr; - /* Write to pty from buffer 1. */ - ptr = remove_iacs(ts, &num_totty); - w = safe_write(ts->ptyfd, ptr, num_totty); - /* needed? if (w < 0 && errno == EAGAIN) continue; */ - if (w < 0) { - if (IS_INETD) - return 0; - free_session(ts); - ts = next; - continue; + struct tsession *next = ts->next; /* in case we free ts */ + + if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) { + /* Write to pty from buffer 1 */ + count = safe_write_to_pty_decode_iac(ts); + if (count < 0) { + if (errno == EAGAIN) + goto skip1; + goto kill_session; } - ts->wridx1 += w; - ts->size1 -= w; - if (ts->wridx1 == BUFSIZE) - ts->wridx1 = 0; } - - if (ts->size2 && FD_ISSET(ts->sockfd_write, &wrfdset)) { - /* Write to socket from buffer 2. */ - maxlen = MIN(BUFSIZE - ts->wridx2, ts->size2); - w = safe_write(ts->sockfd_write, ts->buf2 + ts->wridx2, maxlen); - /* needed? if (w < 0 && errno == EAGAIN) continue; */ - if (w < 0) { - if (IS_INETD) - return 0; - free_session(ts); - ts = next; - continue; + skip1: + if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) { + /* Write to socket from buffer 2 */ + count = MIN(BUFSIZE - ts->wridx2, ts->size2); + count = safe_write_double_iac(ts->sockfd_write, (void*)(TS_BUF2(ts) + ts->wridx2), count); + if (count < 0) { + if (errno == EAGAIN) + goto skip2; + goto kill_session; } - ts->wridx2 += w; - ts->size2 -= w; - if (ts->wridx2 == BUFSIZE) + ts->wridx2 += count; + if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */ + ts->wridx2 = 0; + ts->size2 -= count; + if (ts->size2 == 0) { + ts->rdidx2 = 0; ts->wridx2 = 0; + } } - - if (ts->size1 < BUFSIZE && FD_ISSET(ts->sockfd_read, &rdfdset)) { - /* Read from socket to buffer 1. */ - maxlen = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1); - r = safe_read(ts->sockfd_read, ts->buf1 + ts->rdidx1, maxlen); - if (r < 0 && errno == EAGAIN) continue; - if (r <= 0) { - if (IS_INETD) - return 0; - free_session(ts); - ts = next; - continue; + skip2: + + if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) { + /* Read from socket to buffer 1 */ + count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1); + count = safe_read(ts->sockfd_read, TS_BUF1(ts) + ts->rdidx1, count); + if (count <= 0) { + if (count < 0 && errno == EAGAIN) + goto skip3; + goto kill_session; + } + /* Ignore trailing NUL if it is there */ + if (!TS_BUF1(ts)[ts->rdidx1 + count - 1]) { + --count; } - if (!ts->buf1[ts->rdidx1 + r - 1]) - if (!--r) - continue; - ts->rdidx1 += r; - ts->size1 += r; - if (ts->rdidx1 == BUFSIZE) + ts->size1 += count; + ts->rdidx1 += count; + if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */ ts->rdidx1 = 0; } - - if (ts->size2 < BUFSIZE && FD_ISSET(ts->ptyfd, &rdfdset)) { - /* Read from pty to buffer 2. */ - maxlen = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2); - r = safe_read(ts->ptyfd, ts->buf2 + ts->rdidx2, maxlen); - if (r < 0 && errno == EAGAIN) continue; - if (r <= 0) { - if (IS_INETD) - return 0; - free_session(ts); - ts = next; - continue; + skip3: + if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) { + /* Read from pty to buffer 2 */ + count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2); + count = safe_read(ts->ptyfd, TS_BUF2(ts) + ts->rdidx2, count); + if (count <= 0) { + if (count < 0 && errno == EAGAIN) + goto skip4; + goto kill_session; } - ts->rdidx2 += r; - ts->size2 += r; - if (ts->rdidx2 == BUFSIZE) + ts->size2 += count; + ts->rdidx2 += count; + if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */ ts->rdidx2 = 0; } - - if (ts->size1 == 0) { - ts->rdidx1 = 0; - ts->wridx1 = 0; - } - if (ts->size2 == 0) { - ts->rdidx2 = 0; - ts->wridx2 = 0; - } + skip4: + ts = next; + continue; + kill_session: + if (ts->shell_pid > 0) + update_utmp_DEAD_PROCESS(ts->shell_pid); + free_session(ts); ts = next; } + goto again; }