Bug#996534: netkit-telnet: Specifying a port in telnetrc is not working

[Dongho Chang <dong579@gmail.com>]

Source: netkit-telnet
Version: 0.17
Severity: normal

Dear Maintainer,



# What expected to happen

 - 1. Specify a port in telnetrc ( $HOME/.telnetrc) as follows
     * DEFAUT:8023 mode character
 - 2. telnet a host with specific port
     * telnet 192.168.1.1 8023
 - The expected is that "mode character" command is executed as soon as server is connected, according to "man telnet"

# What happened instead
  - The command in telnetrc specifying a port is not executed
  - But If not specifying a port, the command is executed as expected

# Cause of Bug
  - telnetrc parsing routine ( readrc() function in telnet/command.cc ) has a flaw in comparing the port number of command-line with that of telnetrc
  - To proceed command processing, the result of string compare MUST not negated
  - The patch is as follows
--- a/telnet/commands.cc
+++ b/telnet/commands.cc
@@ -2135,7 +2135,7 @@ static void readrc(const char *m1, const char *m2, const char *port,
                continue;
     while (fgets(line, sizeof(line), rcfile)) {
        ...
        if (gotmachine == 0) {
            ...

            if (line[0] == ':') {
            - if (!strncasecmp(&line[1], port, lport))
            + if (strncasecmp(&line[1], port, lport))
                    continue;
                strncpy(line, &line[lport + 1], sizeof(line) - lport - 1);
            }
           ...
        }
        ...
        process_command(&cmdtab, margc, margv);

-- System Information:
Debian Release: bullseye/sid
  APT prefers focal-updates
  APT policy: (500, 'focal-updates'), (500, 'focal-security'), (500, 'focal'), (100, 'focal-backports')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.11.0-36-generic (SMP w/8 CPU cores)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled