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List: busybox
Subject: RE: busybox Digest, Vol 173, Issue 8
From: Wåglund_Oskar <oskar.waglund () afry ! com>
Date: 2019-12-10 15:09:28
Message-ID: AM0PR01MB4610A146EBC95AB2BC9B5C55915B0 () AM0PR01MB4610 ! eurprd01 ! prod ! exchangelabs ! com
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Hi again,
This issue has been resolved, and did not have to do with telnetd, but with the bash \
settings on the device. Widening the terminal did the trick.
Best regards
Oskar W
-----Original Message-----
From: busybox <busybox-bounces@busybox.net> On Behalf Of busybox-request@busybox.net
Sent: den 9 december 2019 14:42
To: busybox@busybox.net
Subject: busybox Digest, Vol 173, Issue 8
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Today's Topics:
1. Question about telnetd in BusyBox (W?glund Oskar)
----------------------------------------------------------------------
Message: 1
Date: Mon, 9 Dec 2019 13:42:01 +0000
From: W?glund Oskar <oskar.waglund@afry.com>
To: "busybox@busybox.net" <busybox@busybox.net>
Subject: Question about telnetd in BusyBox
Message-ID:
<AM0PR01MB461043D846770A6BA3A840BF91580@AM0PR01MB4610.eurprd01.prod.exchangelabs.com>
Content-Type: text/plain; charset="utf-8"
Hello everyone!
I have had an issue with inetd/telnetd in BusyBox the past couple of days which I \
can?t seem to get around and I was hoping for some friendly advice.
We have recently ported our product to use PetaLinux 2017.3 and with that BusyBox \
(version busybox-1.24.1), and everything has been going very well so far. Now, \
however, our customer has pointed out that sending telnet commands from their test \
framework to our product (which is running the BusyBox telnet daemon) does not work \
in their environment for commands longer than 56 characters. We have observed a \
?weird? behavior that telnetd will split up the echoed response to the client after \
56 characters by adding ?whitespace, carriage return? (ASCII 0x20, 0x0D) before \
continuing the output. This is illustrated in the attached WireShark log and \
screenshot. 10.40.241.50 is the telnetd server and 10.40.241.157 is the telnet \
client.
The result of this is that the Telnet client the customer is using in their test \
framework understands the response when the command entered was 56 characters or less \
long, but adds the entered command to the interpreted response when more characters \
are entered:
Connecting...
Sending:
Sending 56 characters aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
Received:
-sh: Sending: command not found
Disconnected
Connecting...
Sending:
Sending 57 characters aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
Received:
Sending 57 characters aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
a
-sh: Sending: command not found
Disconnected
In the WireShark log you can also see that the Telnet negotiation begins with telnetd \
sending DO ECHO, to which the telnet client responds WON?T ECHO and later DON?T ECHO, \
but this has no effect it seems. I can see in a telnetd.c file in BusyBox that this \
seems to be the case, but I don?t have the option to recompile the code at the \
moment:
/* Make the telnet client understand we will echo characters so it
* should not do it locally. We don't tell the client to run \
linemode,
* because we want to handle line editing and tab completion and \
other
* 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 };
I have also seen a piece of code that seems related to the above mentioned problem \
but haven?t been able to connect the dots:
/* We map \r\n ==> \r for pragmatic reasons.
* Many client \
implementations send \r\n when
* the user hits the \
CarriageReturn key.
* See RFC 1123 3.3.1 \
Telnet End-of-Line Convention.
*/
if (c == '\r' && ptr \
< end && (*ptr == '\n' || *ptr == '\0'))
\
ptr++; continue;
Now my questions to you are
1. Is the added ?0x20, 0x0D? a known issue/feature? (Maybe it is not the telnetd \
client adding it after all?) 2. Is there a way of disabling ECHO in telnetd \
somehow? I have tried desperately to configure this behavior through inetd.cfg and \
inetd.conf but to no avail so far.
I would be most grateful for any advice on this and I would also like to take the \
opportunity to thank you all for the great product that you have produced in BusyBox! \
?
Best regards
Oskar W?glund
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This e-mail may contain confidential and corporate proprietary information. If \
received in error, kindly notify us immediately and delete the communication from \
your system. Our contacts with you may further involve processing of personal data. \
Please read more about how and why ÅF processes personal data on our website \
www.afconsult.com<http://www.afconsult.com/sv/other-pages/privacy-statement/privacy-statement-for-externals/> \
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