Kim Woelders
276 lines
6.8 KiB
C
276 lines
6.8 KiB
C
/*
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* Copyright (c) 2018 Lars Thrane A/S
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* SPDX-License-Identifier: GPL-2.0
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*
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* Telnet protocol handling - server
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*/
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#include <stdlib.h>
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#include <string.h>
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#include "lib/nvt_log.h"
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#include "telnet.h"
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#include "telnet_param.h"
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/* Telnet commands */
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static const char *const tn_cmd[] = {
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"SE", "NOP", "MARK", "BRK", "IP", "AO", "AYT", "EC",
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"EL", "GA", "SB", "WILL", "WONT", "DO", "DONT", "IAC"
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};
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#define OPT_NACK 0 /* Reject (DONT/WONT) */
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#define OPT_IGNORE 1 /* Ignore the command (?) */
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#define OPT_ACK 2 /* Acknowledge (DO /WILL) */
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/* Telnet option support */
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static const unsigned char tn_opt[256] = {
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/* *INDENT-OFF* */
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[TNO_BINARY] = OPT_ACK,
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[TNO_SUPP_GA] = OPT_ACK,
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// [TNO_TTYP] = OPT_NACK,
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// [TNO_NAWS] = OPT_NACK,
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// [TNO_NEO] = OPT_NACK,
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[TNO_CPCO] = OPT_ACK,
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// [TNO_KERMIT] = OPT_NACK,
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/* *INDENT-ON* */
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};
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static void _telnet_handle_req(tn_ctx_t *tcc, int cmd, int opt)
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{
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char buf[3];
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switch (tn_opt[opt])
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{
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default:
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case OPT_IGNORE:
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return;
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case OPT_ACK:
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cmd = (cmd == TNC_FB_WILL) ? TNC_FD_DO : TNC_FB_WILL;
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break;
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case OPT_NACK:
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cmd = (cmd == TNC_FB_WILL) ? TNC_FE_DONT : TNC_FC_WONT;
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break;
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}
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buf[0] = TNC_FF_IAC;
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buf[1] = cmd;
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buf[2] = opt;
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DBG("TNo: Op2 %02x %02x: %-4s %d", cmd, opt, tn_cmd[cmd & 0xf], opt);
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tcc->cli_tx(tcc->cctx, buf, 3);
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if (opt == TNO_CPCO && (cmd == TNC_FB_WILL || cmd == TNC_FD_DO))
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telnet_rfc2217_init(tcc, TNI_ON);
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}
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void telnet_reply_opt(tn_ctx_t *tcc, int opt, int prm,
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const void *val, int len)
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{
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unsigned char buf[128], *pu = buf;
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const unsigned char *pv;
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int i;
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*pu++ = TNC_FF_IAC;
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*pu++ = TNC_FA_SB;
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*pu++ = opt;
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*pu++ = prm;
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if (len > 0 && len <= 32)
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{
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pv = val;
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for (i = 0; i < len; i++)
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{
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*pu++ = *pv;
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if (*pv++ == TNC_FF_IAC)
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*pu++ = TNC_FF_IAC;
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}
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}
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*pu++ = TNC_FF_IAC;
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*pu++ = TNC_F0_SE;
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len = pu - buf;
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DBG2_BUF("opto", buf, len);
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tcc->cli_tx(tcc->cctx, buf, len);
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}
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static void _telnet_handle_opt(tn_ctx_t *tcc, int opt,
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unsigned char *pu, int nd)
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{
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DBG2_BUF("opti", pu, nd);
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switch (opt)
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{
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default:
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nvt_log(LOG_WARNING, "Unexpected SB: Opt = %d", opt);
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break;
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case TNO_CPCO: /* RFC 2217 */
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tcc->mode_rfc2217 = 1;
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telnet_rfc2217_handle_opt(tcc, opt, pu, nd);
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break;
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}
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}
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int telnet_rx(tn_ctx_t *tcc, char *buf, int *plen)
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{
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char *s, *p;
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unsigned char *pu;
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int len, rem;
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int np, nd;
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int b1, b2;
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/* Drop telnet processing entirely if we haven't seen any telnet
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* negotiation in the beginning */
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if (tcc->bytes_rx >= 32 && !tcc->mode_telnet)
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return 0;
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len = *plen;
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tcc->bytes_rx += len;
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if (len < (int)tcc->off_rx)
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tcc->off_rx = 0;
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for (s = buf + tcc->off_rx, rem = len - tcc->off_rx; rem > 0; s = p)
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{
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DBG2_BUF("****", s, rem);
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p = memchr(s, TNC_FF_IAC, rem);
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if (!p)
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break;
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/* We have IAC (= 0xff) */
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np = rem - (p - s); /* N. chars available incl. IAC */
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if (np < 2)
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goto tn_more;
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pu = (unsigned char *)p;
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b1 = pu[1];
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switch (b1)
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{
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default:
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case TNC_F0_SE:
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case TNC_F1_NOP:
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case TNC_F2_MARK:
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case TNC_F3_BRK:
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case TNC_F4_IP:
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case TNC_F5_AO:
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case TNC_F6_AYT:
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case TNC_F7_EC:
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case TNC_F8_EL:
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case TNC_F9_GA:
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DBG("TNi: Op1 %02x : %s", b1, tn_cmd[b1 & 0xf]);
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nd = 2; /* Drop 2 bytes */
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goto tn_drop;
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case TNC_FB_WILL:
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case TNC_FC_WONT:
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case TNC_FD_DO:
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case TNC_FE_DONT:
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if (np < 3)
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goto tn_more; /* Need more */
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tcc->mode_telnet = 1; /* Any such sequence activates TN */
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b2 = pu[2];
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DBG("TNi: Op2 %02x %02x: %-4s %d", b1, b2, tn_cmd[b1 & 0xf], b2);
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if (b1 == TNC_FB_WILL || b1 == TNC_FD_DO)
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_telnet_handle_req(tcc, b1, b2);
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nd = 3; /* Drop 3 bytes */
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goto tn_drop;
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case TNC_FA_SB:
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for (nd = 2; nd < np - 1; nd++)
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{
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if (pu[nd] == TNC_FF_IAC && pu[nd + 1] == TNC_F0_SE)
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{
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nd -= 2;
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if (nd <= 0)
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break;
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b2 = pu[2];
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tcc->mode_telnet = 1; /* Any such sequence activates TN */
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DBG("TNi: Op2 %02x %02x: %-4s %d",
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b1, b2, tn_cmd[b1 & 0xf], b2);
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_telnet_handle_opt(tcc, b2, pu + 3, nd - 1);
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nd += 4;
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goto tn_drop;
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}
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}
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if (np < 16)
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goto tn_more; /* Not done */
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/* This does not look right */
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nvt_log_buf(LOG_WARNING, "tnrx", p, np);
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rem = 0; /* Quit loop */
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break;
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case TNC_FF_IAC:
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p++;
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nd = 1; /* Drop 1 bytes */
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goto tn_drop;
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tn_drop:
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if (!tcc->mode_telnet)
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goto tn_break;
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DBG2_BUF("drop", p, nd);
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rem -= nd + (p - s);
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len -= nd;
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memmove(p, p + nd, rem);
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break;
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tn_break:
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rem = 0; /* Quit loop */
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break;
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tn_more: /* Request more data */
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tcc->off_rx = len - np;
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*plen = len;
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return 1;
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}
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}
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tcc->off_rx = 0;
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*plen = len;
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return 0;
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}
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int telnet_tx(tn_ctx_t *tcc, const char *buf, int len)
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{
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const char *s, *p;
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int rem, nd;
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for (s = buf, rem = len; rem > 0; s = p)
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{
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if (tcc->mode_telnet)
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p = memchr(s, TNC_FF_IAC, rem);
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else
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p = NULL;
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if (!p)
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{
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/* Send the rest */
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nd = rem;
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tcc->cli_tx(tcc->cctx, s, nd);
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}
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else
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{
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nd = p - s + 1;
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tcc->cli_tx(tcc->cctx, s, nd);
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tcc->cli_tx(tcc->cctx, p, 1); /* One TNC_FF_IAC */
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p++;
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}
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rem -= nd;
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}
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return 0;
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}
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tn_ctx_t *telnet_ctx_init(void *cctx, cli_tx_f *ftx, cli_ss_f *fss)
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{
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tn_ctx_t *tcc;
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tcc = calloc(1, sizeof(tn_ctx_t));
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tcc->cctx = cctx;
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tcc->cli_tx = ftx; /* Write to client */
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tcc->cli_ss = fss; /* Set state (line/modem) */
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telnet_rfc2217_init(tcc, TNI_INIT);
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return tcc;
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}
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