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telnetd: treat all 2-byte IACs in 240..249 range as NOPs.

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A bit of future-proofing. Some of them can stand just being ignored.

function                                             old     new   delta
telnetd_main                                        1791    1798      +7

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2016-10-12 19:41:33 +02:00
parent 122c47ac02
commit b6d421b635
1 changed files with 24 additions and 18 deletions
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42
networking/telnetd.c
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@ -169,12 +169,10 @@ safe_write_to_pty_decode_iac(struct tsession *ts)
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)?
* Implemented only as part of NAWS:
* IAC SB (250) Subnegotiation of an option follows.
* IAC SE (240) End of subnegotiation.
* 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).
@ -182,8 +180,11 @@ safe_write_to_pty_decode_iac(struct tsession *ts)
* 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) */
if (buf[1] == IAC) {
/* Literal 255 (emacs M-DEL) */
//bb_error_msg("255!");
rc = safe_write(ts->ptyfd, &buf[1], 1);
if (rc <= 0)
@ -191,7 +192,9 @@ safe_write_to_pty_decode_iac(struct tsession *ts)
rc = 2;
goto update_and_return;
}
if (buf[1] == NOP) { /* NOP (241). Ignore (putty keepalive, etc) */
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;
}
@ -205,24 +208,27 @@ safe_write_to_pty_decode_iac(struct tsession *ts)
goto update_and_return;
}
/* TELOPT_NAWS support */
/* IAC SB, TELOPT_NAWS, 4-byte, IAC SE */
if (buf[1] == SB && buf[2] == TELOPT_NAWS) {
struct winsize ws;
if (wr <= 8) {
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;
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;
}
memset(&ws, 0, sizeof(ws));
ws.ws_col = (buf[3] << 8) | buf[4];
ws.ws_row = (buf[5] << 8) | buf[6];
ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
rc = 9;
goto update_and_return;
/* else: other subnegs not supported yet */
}
/* Skip 3-byte cmds (assume they are WILL/WONT/DO/DONT 251..254 codes) */
/* 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]));