8738c3102
Denys Vlasenko
2026-02-22
Subject
telnetd: fix handshake: had one wrong, but harmless element
Binary
No binary (build failed)
Architecture & Compiler Flags
gcc -Wp,-MD,applets/.usage.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -Iinclude -Iinclude -o applets/usage applets/usage.c
Build Log
(log yok)
Commit Diff GitHub →
networking/telnet.txt+1 -1
| @@ -2,7 +2,7 @@ | |
| // IAC SE (240) End of subnegotiation parameters | |
| // IAC NOP (241) No operation | |
| // IAC DM (242) Data Mark (used with TCP urgent pointer) | |
| - | // IAC BRK (243) Break (simulate serial line break) - perhaps tcsendbreak(master_ptyfd, 0) [untested]? |
| + | // IAC BRK (243) Break (simulate serial line break) - perhaps tcsendbreak(master_ptyfd)? [untested] |
| // IAC IP (244) Interrupt Process ("send SIGINT to foreground process group a-la ^C") | |
| // IAC AO (245) Abort Output | |
| // IAC AYT (246) Are You There | |
networking/telnetd.c+14 -6
| @@ -866,13 +866,21 @@ static void make_new_session(ioloop_state_t *io, int sockrd) | |
| * stuff that requires char-by-char support. */ | |
| { | |
| 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 |
| + | IAC, WILL, TELOPT_ECHO, // "I will echo your chars" |
| + | // (Not really, _we_ won't - our programs in pty usually |
| + | // handle that. In practice, this says: "do not echo |
| + | // your user's input chars back to him _on your side_".) |
| + | IAC, WILL, TELOPT_SGA, // "I assume full-duplex, won't send GA's" |
| + | //IAC, DO, TELOPT_ECHO, //WRONG: "can you echo my chars to me"?? |
| + | IAC, DO, TELOPT_NAWS, // "can you send me terminal size data?" |
| + | // This requires telnetd.ctrlSQ.patch (incomplete): |
| + | //IAC, DO, TELOPT_LFLOW, |
| }; | |
| + | //Theoretically, our "WILL X" are requests and should only activate when client responds with "DO X". |
| + | //However, we do not wait/check for "DO"s. Why? |
| + | //There is nothing to "activate" on our side for TELOPT_ECHO. |
| + | //For TELOPT_SGA, we don't even have code to support sending/understandig GAs, |
| + | //so SGA is "always activated". |
| /* Just stuff it into TCP stream! (no error check...) */ | |
| safe_write(sockwr, iacs_to_send, sizeof(iacs_to_send)); | |
| } | |