sys/net/application_layer: add telnet server module & example #16723

benpicco · 2021-08-10T21:48:55Z

Contribution description

Quite often a remote shell would be handy to have. Telnet is a simple and ubiquitous protocol to achieve just that, on most systems no additional tools are needed.

Telnet is entirely unencrypted and we do no authentication, so only use this for debugging. Yet for debugging, having remote access to a sensor can be pretty useful.

Limitations

~~does not work on native~~
after disconnecting, one has to wait for 2 Minutes before a new connection is possible. See gnrc_sock_tcp: add gnrc sock tcp #16494 (comment)

Testing procedure

There is an example application in

examples/telnet_server

It will print it's IP address via UART, connect to it using the telnet utility:

2021-08-18 15:39:01,390 # main(): This is RIOT! (Version: 2021.10-devel-374-g16cfd-gnrc_sock_tcp-telnet)
2021-08-18 15:39:01,392 # RIOT telnet example application
2021-08-18 15:39:01,396 # My address is fe80::a4ed:29ff:feec:cbf3
2021-08-18 15:39:01,398 # All up, awaiting connection

% telnet fe80::a4ed:29ff:feec:cbf3%eno1
Trying fe80::a4ed:29ff:feec:cbf3%eno1...
Connected to fe80::a4ed:29ff:feec:cbf3%eno1.
Escape character is '^]'.

> ps
	pid | name                 | state    Q | pri | stack  ( used) ( free) | base addr  | current     
	  - | isr_stack            | -        - |   - |    512 (  232) (  280) | 0x20000000 | 0x200001c8
	  1 | main                 | running  Q |   7 |   1536 ( 1260) (  276) | 0x200002c0 | 0x2000052c 
	  2 | ipv6                 | bl rx    _ |   4 |   1024 (  528) (  496) | 0x2000099c | 0x20000c84 
	  3 | gnrc_tcp             | bl rx    _ |   5 |   1024 (  416) (  608) | 0x20002dec | 0x2000307c 
	  4 | sam0_eth             | bl rx    _ |   2 |   1024 (  504) (  520) | 0x20001188 | 0x2000144c 
	  5 | telnet               | bl mbox  _ |   6 |   1024 (  672) (  352) | 0x20006934 | 0x20006b74 
	    | SUM                  |            |     |   6144 ( 3612) ( 2532)

> ifconfig
Iface  4  HWaddr: A6:ED:29:EC:CB:F3 
          L2-PDU:1500  MTU:1492  HL:255  Source address length: 6
          Link type: wired
          inet6 addr: fe80::a4ed:29ff:feec:cbf3  scope: link  VAL
          inet6 addr: 2001:16b8:4500:5f00:a4ed:29ff:feec:cbf3  scope: global  VAL
          inet6 group: ff02::1
          inet6 group: ff02::1:ffec:cbf3
          
>

Issues/PRs references

based on benemorius@ab97e2d
#16822 is needed to work on native

miri64 · 2021-08-24T11:30:48Z

Telnet is entirely encrypted and we do no authentication, so only use this for debugging. Yet for debugging, having remote access to a sensor can be pretty useful.

Shoud there maybe be a big friendly in-code warning about this?

miri64 · 2021-09-06T19:58:13Z

Shoud there maybe be a big friendly in-code warning about this?

Ping?

sys/include/net/telnet.h

no longer relevant (change is done)

chrysn · 2022-02-15T10:41:01Z

What is still missing here to push this forward?

Probably primarily someone who really supports it. I won't block this on my own (for lack of quick alternatives), but I still think it's a bad idea to have around, and I won't sign off on it.

Proposal that came up during the sprint today: Having this as an out-of-tree contrib module might be a good idea. It'd be something that only happens when users very actively opt in, would be an opportunity to hone and show off our ability to use modules from outside, and also work as a showcase or scaffolding that people can build other stuff from (like, not using console but showing videos).

kfessel · 2022-02-15T11:22:01Z

Zephyr has Telnet
https://docs.zephyrproject.org/samples/net/telnet/README.html

implemented as a shell backend (so not just that one example)
https://github.com/zephyrproject-rtos/zephyr/tree/main/subsys/shell/backends
there are 3 backend uart, rtt (serialdebug segger), and telnet

FreeRTOS+TCP has TCP IO for CLI as one of their prime examples
https://www.freertos.org/FreeRTOS-Plus/FreeRTOS_Plus_TCP/TCP_CLI.html

makefiles/dependency_resolution.inc.mk

maribu · 2022-02-17T01:03:15Z

I can test tomorrow, then this can get it.

I'm pretty sure that nobody uses this by accident or unaware of security implications with the big fat warning an the I_UNDERSTAND_THAT_TELNET_IS_INSECURE environment variable being set to 1. I bet this telnet server is now better locked away behind child safety locks than 99% of the other implementations out there.

maribu · 2022-03-01T21:16:31Z

please rebase and squash

This reverts d03175c

benpicco · 2022-03-01T22:10:34Z

same54-xpro

% telnet fe80::fec2:3dff:fe0b:d44f%eno1
Trying fe80::fec2:3dff:fe0b:d44f%eno1...
Connected to fe80::fec2:3dff:fe0b:d44f%eno1.
Escape character is '^]'.
RIOT telnet example application
╔═══════════════════════════════════════════════════╗
║telnet is entirely unencrypted and unauthenticated.║
║Do not use this on public networks.                ║
╚═══════════════════════════════════════════════════╝
ps
ps
	pid | name                 | state    Q | pri | stack  ( used) ( free) | base addr  | current     
	  - | isr_stack            | -        - |   - |    512 (  292) (  220) | 0x20000000 | 0x200001c8
	  1 | main                 | running  Q |   7 |   1536 ( 1276) (  260) | 0x20000300 | 0x2000055c 
	  2 | ipv6                 | bl rx    _ |   4 |   1024 (  500) (  524) | 0x200009dc | 0x20000cc4 
	  3 | gnrc_tcp             | bl rx    _ |   5 |   1024 (  440) (  584) | 0x20002e24 | 0x200030b4 
	  4 | sam0_eth             | bl rx    _ |   2 |   1024 (  536) (  488) | 0x200011c0 | 0x20001484 
	  5 | telnet               | bl mbox  _ |   6 |   1024 (  792) (  232) | 0x20006934 | 0x20006b74 
	    | SUM                  |            |     |   6144 ( 3836) ( 2308)
> 
> ifconfig
ifconfig
Iface  4  HWaddr: FC:C2:3D:0B:D4:4F 
          L2-PDU:1500  MTU:1492  HL:255  Source address length: 6
          Link type: wired
          inet6 addr: fe80::fec2:3dff:fe0b:d44f  scope: link  VAL
          inet6 addr: 2001:16b8:456d:3000:fec2:3dff:fe0b:d44f  scope: global  VAL
          inet6 group: ff02::1
          inet6 group: ff02::1:ff0b:d44f
          
> 
> ping ff02::1
ping ff02::1
12 bytes from fe80::fe08:c033:940c:7e79%4: icmp_seq=0 ttl=255 time=0.415 ms
12 bytes from fe80::eade:27ff:fec8:b1c3%4: icmp_seq=0 ttl=64 time=52.324 ms (DUP!)
12 bytes from fe80::de39:6fff:fe6a:6980%4: icmp_seq=0 ttl=64 time=104.050 ms (DUP!)
12 bytes from fe80::215:99ff:fe8c:6c5d%4: icmp_seq=0 ttl=255 time=155.761 ms (DUP!)
12 bytes from fe80::4ba:96ff:fe2b:46eb%4: icmp_seq=0 ttl=255 time=207.495 ms (DUP!)
12 bytes from fe80::185f:9217:c8eb:757b%4: icmp_seq=0 ttl=255 time=259.361 ms (DUP!)
12 bytes from fe80::fe08:c033:940c:7e79%4: icmp_seq=1 ttl=255 time=0.290 ms
12 bytes from fe80::4ba:96ff:fe2b:46eb%4: icmp_seq=1 ttl=255 time=13.439 ms (DUP!)
12 bytes from fe80::eade:27ff:fec8:b1c3%4: icmp_seq=1 ttl=64 time=65.085 ms (DUP!)
12 bytes from fe80::de39:6fff:fe6a:6980%4: icmp_seq=1 ttl=64 time=116.737 ms (DUP!)
12 bytes from fe80::215:99ff:fe8c:6c5d%4: icmp_seq=1 ttl=255 time=168.416 ms (DUP!)
12 bytes from fe80::f272:eaff:feef:b75%4: icmp_seq=1 ttl=64 time=220.051 ms (DUP!)
12 bytes from fe80::fe08:c033:940c:7e79%4: icmp_seq=2 ttl=255 time=0.349 ms

--- ff02::1 PING statistics ---
3 packets transmitted, 3 packets received, 10 duplicates, 0% packet loss
round-trip min/avg/max = 0.290/104.905/259.361 ms
>

native

% telnet fe80::7837:fcff:fe7d:1aaf%tapbr0
Trying fe80::7837:fcff:fe7d:1aaf%tapbr0...
Connected to fe80::7837:fcff:fe7d:1aaf%tapbr0.
Escape character is '^]'.
RIOT telnet example application
╔═══════════════════════════════════════════════════╗
║telnet is entirely unencrypted and unauthenticated.║
║Do not use this on public networks.                ║
╚═══════════════════════════════════════════════════╝
ps
ps
	pid | name                 | state    Q | pri | stack  ( used) ( free) | base addr  | current     
	  - | isr_stack            | -        - |   - |   8192 (   -1) ( 8193) |  0x8081880 |  0x8081880
	  1 | idle                 | pending  Q |  15 |   8192 ( 1084) ( 7108) |  0x807a180 |  0x807bfe0 
	  2 | main                 | running  Q |   7 |  12288 ( 3004) ( 9284) |  0x807c180 |  0x807efe0 
	  3 | ipv6                 | bl rx    _ |   4 |   8192 ( 1648) ( 6544) |  0x8085c20 |  0x8087a80 
	  4 | gnrc_tcp             | bl rx    _ |   5 |   8192 ( 1696) ( 6496) |  0x808b8e0 |  0x808d740 
	  5 | gnrc_netdev_tap      | bl rx    _ |   2 |   8192 ( 2492) ( 5700) |  0x8088040 |  0x8089ea0 
	  6 | telnet               | bl mbox  _ |   6 |   8192 ( 2580) ( 5612) |  0x808e4c0 |  0x8090320 
	    | SUM                  |            |     |  61440 (12504) (48936)
> 
> ifconfig
ifconfig
Iface  5  HWaddr: 7A:37:FC:7D:1A:AF 
          L2-PDU:1500  MTU:1500  HL:64  Source address length: 6
          Link type: wired
          inet6 addr: fe80::7837:fcff:fe7d:1aaf  scope: link  VAL
          inet6 group: ff02::1
          inet6 group: ff02::1:ff7d:1aaf
          
> 
> ping ff02::1
ping ff02::1
12 bytes from fe80::90a7:a6ff:fe4b:2e32%5: icmp_seq=0 ttl=64 time=0.106 ms
12 bytes from fe80::90a7:a6ff:fe4b:2e32%5: icmp_seq=1 ttl=64 time=0.129 ms
12 bytes from fe80::90a7:a6ff:fe4b:2e32%5: icmp_seq=2 ttl=64 time=0.126 ms

--- ff02::1 PING statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.106/0.120/0.129 ms
>

maribu

ACK. Code looks good, @benpicco provided testing results, and child safety measures to prevent accidental or uninformed use are in place.

benpicco · 2022-03-02T07:14:59Z

Thank you for the review! 😃

benpicco changed the title ~~add telnet server module & example~~ sys/net/application_layer: add telnet server module & example Aug 10, 2021

benpicco added Area: network Area: Networking State: WIP State: The PR is still work-in-progress and its code is not in its final presentable form yet labels Aug 10, 2021

benpicco requested a review from brummer-simon August 10, 2021 21:53

hugueslarrive mentioned this pull request Aug 12, 2021

dist/tools/pyterm: ipv6 address support for tcp_serial option #16726

Merged

benpicco force-pushed the gnrc_sock_tcp-telnet branch from 69ddeb8 to ff8fd67 Compare August 15, 2021 17:52

github-actions bot added Area: build system Area: Build system Area: examples Area: Example Applications Area: sys Area: System labels Aug 15, 2021

benpicco force-pushed the gnrc_sock_tcp-telnet branch 3 times, most recently from a0c8bae to 083c195 Compare August 17, 2021 15:57

benpicco requested a review from benemorius August 17, 2021 16:03

benpicco force-pushed the gnrc_sock_tcp-telnet branch from 083c195 to eb945bd Compare August 18, 2021 13:39

benpicco removed the State: WIP State: The PR is still work-in-progress and its code is not in its final presentable form yet label Aug 18, 2021

benpicco marked this pull request as ready for review August 18, 2021 13:41

benpicco requested review from cgundogan, haukepetersen, maribu, miri64 and PeterKietzmann as code owners August 18, 2021 13:41

benpicco force-pushed the gnrc_sock_tcp-telnet branch from eb945bd to 8828119 Compare August 18, 2021 13:46

benpicco added the Type: new feature The issue requests / The PR implemements a new feature for RIOT label Aug 18, 2021

benpicco requested a review from chrysn August 27, 2021 21:46

benpicco force-pushed the gnrc_sock_tcp-telnet branch from 8828119 to 2173c1f Compare September 6, 2021 19:37

benpicco requested a review from kfessel September 6, 2021 19:43

benpicco commented Sep 6, 2021

View reviewed changes

sys/include/net/telnet.h Outdated Show resolved Hide resolved

miri64 reviewed Sep 7, 2021

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sys/include/net/telnet.h Outdated Show resolved Hide resolved

benpicco requested a review from JKRhb January 13, 2022 20:49

maribu reviewed Feb 16, 2022

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makefiles/dependency_resolution.inc.mk Outdated Show resolved Hide resolved

benpicco requested a review from maribu February 23, 2022 15:41

benpicco and others added 4 commits March 1, 2022 23:07

net/gnrc: restore inclusion of net/gnrc/tcp.h

1b52dee

This reverts d03175c

sys/net/application_layer: add telnet server module

2034fa5

examples/telnet_server: add telnet server example

c476abe

makefiles: warn if telnet is used in auto-init mode

2e46e4a

benpicco force-pushed the gnrc_sock_tcp-telnet branch from 2a5d4ac to 2e46e4a Compare March 1, 2022 22:08

maribu approved these changes Mar 2, 2022

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maribu enabled auto-merge March 2, 2022 06:28

maribu merged commit fbe73b7 into RIOT-OS:master Mar 2, 2022

benpicco deleted the gnrc_sock_tcp-telnet branch March 2, 2022 07:14

chrysn mentioned this pull request Mar 2, 2022

Question: Shell commands via telnet #12233

Closed

kfessel mentioned this pull request Mar 2, 2022

sys,examples,tests,fuzzing: add missing includes #17714

Merged

chrysn mentioned this pull request Mar 11, 2022

sys/shell: new module shell_lock #13082

Merged

OlegHahm added this to the Release 2022.04 milestone Apr 25, 2022

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sys/net/application_layer: add telnet server module & example #16723

sys/net/application_layer: add telnet server module & example #16723

benpicco commented Aug 10, 2021 •

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miri64 commented Aug 24, 2021

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maribu commented Feb 17, 2022

maribu commented Mar 1, 2022

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benpicco commented Mar 2, 2022

sys/net/application_layer: add telnet server module & example #16723

sys/net/application_layer: add telnet server module & example #16723

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benpicco commented Aug 10, 2021 • edited Loading

Contribution description

Limitations

Testing procedure

Issues/PRs references

miri64 commented Aug 24, 2021

miri64 commented Sep 6, 2021

chrysn commented Feb 15, 2022

kfessel commented Feb 15, 2022 • edited Loading

maribu commented Feb 17, 2022

maribu commented Mar 1, 2022

benpicco commented Mar 1, 2022

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benpicco commented Aug 10, 2021 •

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kfessel commented Feb 15, 2022 •

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