GNU bug report logs - #20246
25.0.50; Tramp does not show correct error message when ssh refuses to connect to host due to changed host key

Previous Next

To add a comment to this bug, you must first unarchive it, by sending
a message to control AT debbugs.gnu.org, with unarchive 20246 in the body.
You can then email your comments to 20246 AT debbugs.gnu.org in the normal way.

Toggle the display of automated, internal messages from the tracker.

Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Filipp Gunbin <fgunbin <at> fastmail.fm>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.0.50;
 Tramp does not show correct error message when ssh refuses to connect
 to host due to changed host key
Date: Thu, 02 Apr 2015 17:10:03 +0300

When I try to connect to a host and that host's key differs from what I
have in ~/.ssh/known_hosts Tramp does not handle that correctly.

SSH suspects an attack, but in my case it is not.

I suppose Tramp could show the full error message emitted by ssh.

Filipp


*Messages*:

Tramp: Opening connection for fgunbin@<myhost> using ssh...
Tramp: Sending command `exec ssh -l fgunbin  -o ControlMaster=auto -o ControlPath='tramp.%C' -o ControlPersist=no -e none <myhost>'
Tramp: Waiting for prompts from remote shell...failed
Tramp: Opening connection for fgunbin@<myhost> using ssh...failed


tramp debug buffer:

16:58:00.853274 tramp-process-one-action (5) # Looking for regexp "\(\)\'" from remote shell
16:58:00.853332 tramp-process-one-action (5) # Call `tramp-action-process-alive'
16:58:00.853511 tramp-process-actions (6) # 
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
SHA256:<fingerprint>.
Please contact your system administrator.
Add correct host key in /Users/fgunbin/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /Users/fgunbin/.ssh/known_hosts:67
ECDSA host key for <myhost> has changed and you have requested strict checking.
Host key verification failed.
16:58:00.853619 tramp-process-sentinel (5) # Sentinel called: `#<process *tramp/ssh fgunbin@<myhost>*>' `exited abnormally with code 255
'
16:58:00.855144 tramp-process-actions (1) # File error: Tramp failed to connect.  If this happens repeatedly, try
    `M-x tramp-cleanup-this-connection'
16:58:00.855824 tramp-maybe-open-connection (3) # Opening connection for fgunbin@<myhost> using ssh...failed
16:58:00.858610 tramp-get-remote-perl (5) # Finding a suitable `perl' command
16:58:00.858762 tramp-file-name-handler (1) # Suppress received in operation (file-name-all-completions var /ssh:fgunbin@<myhost>:/)
16:58:00.861488 tramp-get-remote-perl (5) # Finding a suitable `perl' command
16:58:00.861661 tramp-file-name-handler (1) # Suppress received in operation (file-name-all-completions  /ssh:fgunbin@<myhost>:/)


Usual bug-report stuff:

In GNU Emacs 25.0.50.1 (x86_64-apple-darwin14.1.0)
 of 2015-03-12 on fgunbin.local
Repository revision: 2401274b239e837ec274b373ba0f2848faaea7b2
Configured using:
 `configure --without-all --with-xml2 --without-x --with-wide-int'

Configured features:
LIBXML2

Message #8 received at 20246 <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: Filipp Gunbin <fgunbin <at> fastmail.fm>
Cc: 20246 <at> debbugs.gnu.org
Subject: Re: bug#20246: 25.0.50;
 Tramp does not show correct error message when ssh refuses to connect
 to host due to changed host key
Date: Fri, 03 Apr 2015 12:05:19 +0200

Filipp Gunbin <fgunbin <at> fastmail.fm> writes:

> When I try to connect to a host and that host's key differs from what I
> have in ~/.ssh/known_hosts Tramp does not handle that correctly.
>
> SSH suspects an attack, but in my case it is not.
>
> I suppose Tramp could show the full error message emitted by ssh.
>
> 16:58:00.853511 tramp-process-actions (6) #
> @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
> @    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
> @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
> IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
> Someone could be eavesdropping on you right now (man-in-the-middle attack)!
> It is also possible that a host key has just been changed.
> The fingerprint for the ECDSA key sent by the remote host is
> SHA256:<fingerprint>.
> Please contact your system administrator.
> Add correct host key in /Users/fgunbin/.ssh/known_hosts to get rid of this message.
> Offending ECDSA key in /Users/fgunbin/.ssh/known_hosts:67
> ECDSA host key for <myhost> has changed and you have requested strict checking.
> Host key verification failed.
> 16:58:00.853619 tramp-process-sentinel (5) # Sentinel called: `#<process *tramp/ssh fgunbin@<myhost>*>' `exited abnormally with code 255
> '

Usually, Tramp shows the connection buffer in this error case,
containing all these messages. Doesn't it happen for you?

It shows this buffer for 30 seconds, or until you hit a key.

> Filipp

Best regards, Michael.

Message #11 received at 20246 <at> debbugs.gnu.org (full text, mbox):

From: Filipp Gunbin <fgunbin <at> fastmail.fm>
To: Michael Albinus <michael.albinus <at> gmx.de>
Cc: 20246 <at> debbugs.gnu.org
Subject: Re: bug#20246: 25.0.50;
 Tramp does not show correct error message when ssh refuses to connect
 to host due to changed host key
Date: Thu, 09 Apr 2015 23:07:00 +0300

On 03/04/2015 12:05 +0200, Michael Albinus wrote:

> Usually, Tramp shows the connection buffer in this error case,
> containing all these messages. Doesn't it happen for you?
>
> It shows this buffer for 30 seconds, or until you hit a key.

That's what I can reproduce now:

- change host identity in ~/.ssh/known-host
- M-x tramp-cleanup-all-connections
- C-x 4 r /ssh:user <at> host:/file

Now, Tramp shows correct error message from ssh.

- now, quit it with C-]
- again C-x 4 r (as above)

Now Tramp shows in the echo area: "/ssh:user <at> host:/file does not exist"

This is the behavior which takes place if the above steps are done
rather quickly.

If I take a pause before retrying to visit a file, ssh error message is
shown correctly.

Maybe this is not the same problem I had originally, but that's what
I'm able to reproduce right now.

Filipp

Message #14 received at 20246 <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: Filipp Gunbin <fgunbin <at> fastmail.fm>
Cc: 20246 <at> debbugs.gnu.org
Subject: Re: bug#20246: 25.0.50;
 Tramp does not show correct error message when ssh refuses to connect
 to host due to changed host key
Date: Fri, 10 Apr 2015 16:38:18 +0200

Filipp Gunbin <fgunbin <at> fastmail.fm> writes:

Hi Filipp,

> That's what I can reproduce now:
>
> - change host identity in ~/.ssh/known-host
> - M-x tramp-cleanup-all-connections
> - C-x 4 r /ssh:user <at> host:/file
>
> Now, Tramp shows correct error message from ssh.

OK.

> - now, quit it with C-]
> - again C-x 4 r (as above)
>
> Now Tramp shows in the echo area: "/ssh:user <at> host:/file does not exist"
>
> This is the behavior which takes place if the above steps are done
> rather quickly.

"rather quickly" means within 10 seconds. This is the default value of
`remote-file-name-inhibit-cache', the time Tramp keeps its cache for a
given file.

> If I take a pause before retrying to visit a file, ssh error message is
> shown correctly.

OK.

> Maybe this is not the same problem I had originally, but that's what
> I'm able to reproduce right now.

Could you, please, apply the following patch:

--8<---------------cut here---------------start------------->8---
*** /home/albinus/src/tramp/lisp/tramp.el.~master~	2015-04-10 16:34:06.421074752 +0200
--- /home/albinus/src/tramp/lisp/tramp.el	2015-04-10 16:29:29.236143227 +0200
***************
*** 3558,3563 ****
--- 3558,3565 ----
  	  (tramp-message vec 6 "\n%s" (buffer-string)))
  	(unless (eq exit 'ok)
  	  (tramp-clear-passwd vec)
+ 	  (tramp-flush-directory-property vec "")
+ 	  (tramp-flush-connection-property proc)
  	  (delete-process proc)
  	  (tramp-error-with-buffer
  	   (tramp-get-connection-buffer vec) vec 'file-error
--8<---------------cut here---------------end--------------->8---

This changes the behaviour that Tramp doesn't keep its cache anymore,
when there is an error during connection. Tramp reports that the
file/directory doesn't exist, and Emacs falls back to its default
behaviour, offering you a new empty buffer. This sounds consistent.

> Filipp

Best regards, Michael.

Message #17 received at 20246 <at> debbugs.gnu.org (full text, mbox):

From: Filipp Gunbin <fgunbin <at> fastmail.fm>
To: Michael Albinus <michael.albinus <at> gmx.de>
Cc: 20246 <at> debbugs.gnu.org
Subject: Re: bug#20246: 25.0.50;
 Tramp does not show correct error message when ssh refuses to connect
 to host due to changed host key
Date: Tue, 14 Apr 2015 21:52:16 +0300

Michael,

On 10/04/2015 16:38 +0200, Michael Albinus wrote:

> Could you, please, apply the following patch:
>
> *** /home/albinus/src/tramp/lisp/tramp.el.~master~	2015-04-10 16:34:06.421074752 +0200
> --- /home/albinus/src/tramp/lisp/tramp.el	2015-04-10 16:29:29.236143227 +0200
> ***************
> *** 3558,3563 ****
> --- 3558,3565 ----
>   	  (tramp-message vec 6 "\n%s" (buffer-string)))
>   	(unless (eq exit 'ok)
>   	  (tramp-clear-passwd vec)
> + 	  (tramp-flush-directory-property vec "")
> + 	  (tramp-flush-connection-property proc)
>   	  (delete-process proc)
>   	  (tramp-error-with-buffer
>   	   (tramp-get-connection-buffer vec) vec 'file-error
>
> This changes the behaviour that Tramp doesn't keep its cache anymore,
> when there is an error during connection. Tramp reports that the
> file/directory doesn't exist, and Emacs falls back to its default
> behaviour, offering you a new empty buffer. This sounds consistent.

Thanks, I applied the patch (using tramp from git master), but nothing
changed.

Also, it seems that the error messages start to appear after a smaller
period of time than `remote-file-name-inhibit-cache' (which is 10,
indeed).

Filipp

Message #20 received at 20246 <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: Filipp Gunbin <fgunbin <at> fastmail.fm>
Cc: 20246 <at> debbugs.gnu.org
Subject: Re: bug#20246: 25.0.50;
 Tramp does not show correct error message when ssh refuses to connect
 to host due to changed host key
Date: Thu, 16 Apr 2015 16:30:39 +0200

Filipp Gunbin <fgunbin <at> fastmail.fm> writes:

> Michael,

Hi Filipp,

>> Could you, please, apply the following patch:
>>
>> *** /home/albinus/src/tramp/lisp/tramp.el.~master~	2015-04-10 16:34:06.421074752 +0200
>> --- /home/albinus/src/tramp/lisp/tramp.el	2015-04-10 16:29:29.236143227 +0200
>> ***************
>> *** 3558,3563 ****
>> --- 3558,3565 ----
>>   	  (tramp-message vec 6 "\n%s" (buffer-string)))
>>   	(unless (eq exit 'ok)
>>   	  (tramp-clear-passwd vec)
>> + 	  (tramp-flush-directory-property vec "")
>> + 	  (tramp-flush-connection-property proc)
>>   	  (delete-process proc)
>>   	  (tramp-error-with-buffer
>>   	   (tramp-get-connection-buffer vec) vec 'file-error
>>
>> This changes the behaviour that Tramp doesn't keep its cache anymore,
>> when there is an error during connection. Tramp reports that the
>> file/directory doesn't exist, and Emacs falls back to its default
>> behaviour, offering you a new empty buffer. This sounds consistent.
>
> Thanks, I applied the patch (using tramp from git master), but nothing
> changed.
>
> Also, it seems that the error messages start to appear after a smaller
> period of time than `remote-file-name-inhibit-cache' (which is 10,
> indeed).

Hmm, strange. Have you tested starting with "emacs -Q"?

> Filipp

Best regards, Michael.

Message #23 received at 20246 <at> debbugs.gnu.org (full text, mbox):

From: Filipp Gunbin <fgunbin <at> fastmail.fm>
To: Michael Albinus <michael.albinus <at> gmx.de>
Cc: 20246 <at> debbugs.gnu.org
Subject: Re: bug#20246: 25.0.50;
 Tramp does not show correct error message when ssh refuses to connect
 to host due to changed host key
Date: Fri, 08 May 2015 13:36:38 +0300

On 16/04/2015 16:30 +0200, Michael Albinus wrote:

> Filipp Gunbin <fgunbin <at> fastmail.fm> writes:
>
>> Michael,
>
> Hi Filipp,
>
>>> Could you, please, apply the following patch:
>>>
>>> *** /home/albinus/src/tramp/lisp/tramp.el.~master~	2015-04-10 16:34:06.421074752 +0200
>>> --- /home/albinus/src/tramp/lisp/tramp.el	2015-04-10 16:29:29.236143227 +0200
>>> ***************
>>> *** 3558,3563 ****
>>> --- 3558,3565 ----
>>>   	  (tramp-message vec 6 "\n%s" (buffer-string)))
>>>   	(unless (eq exit 'ok)
>>>   	  (tramp-clear-passwd vec)
>>> + 	  (tramp-flush-directory-property vec "")
>>> + 	  (tramp-flush-connection-property proc)
>>>   	  (delete-process proc)
>>>   	  (tramp-error-with-buffer
>>>   	   (tramp-get-connection-buffer vec) vec 'file-error
>>>
>>> This changes the behaviour that Tramp doesn't keep its cache anymore,
>>> when there is an error during connection. Tramp reports that the
>>> file/directory doesn't exist, and Emacs falls back to its default
>>> behaviour, offering you a new empty buffer. This sounds consistent.
>>
>> Thanks, I applied the patch (using tramp from git master), but nothing
>> changed.
>>
>> Also, it seems that the error messages start to appear after a smaller
>> period of time than `remote-file-name-inhibit-cache' (which is 10,
>> indeed).
>
> Hmm, strange. Have you tested starting with "emacs -Q"?

Hi Michael, sorry for delay.

I tried with "emacs -Q -L ~/src/tramp/lisp", the result is the same.

Filipp

Message #26 received at 20246 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Filipp Gunbin <fgunbin <at> fastmail.fm>
Cc: 20246 <at> debbugs.gnu.org
Subject: Re: bug#20246: 25.0.50; Tramp does not show correct error message
 when ssh refuses to connect to host due to changed host key
Date: Mon, 24 Jan 2022 17:12:59 +0100

Filipp Gunbin <fgunbin <at> fastmail.fm> writes:

> When I try to connect to a host and that host's key differs from what I
> have in ~/.ssh/known_hosts Tramp does not handle that correctly.
>
> SSH suspects an attack, but in my case it is not.
>
> I suppose Tramp could show the full error message emitted by ssh.

(I'm going through old bug reports that unfortunately weren't resolved
at the time.)

I tried reproducing this under "emacs -Q" with Emacs 28/29, but Tramp
pops up the full ssh message buffer, so I don't seem to be able to
reproduce the problem.  Are you still seeing the problem in recent Emacs
versions?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #31 received at 20246 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Filipp Gunbin <fgunbin <at> fastmail.fm>
Cc: 20246 <at> debbugs.gnu.org
Subject: Re: bug#20246: 25.0.50; Tramp does not show correct error message
 when ssh refuses to connect to host due to changed host key
Date: Tue, 22 Feb 2022 02:05:32 +0100

Lars Ingebrigtsen <larsi <at> gnus.org> writes:

> I tried reproducing this under "emacs -Q" with Emacs 28/29, but Tramp
> pops up the full ssh message buffer, so I don't seem to be able to
> reproduce the problem.  Are you still seeing the problem in recent Emacs
> versions?

More information was requested, but no response was given within a
month, so I'm closing this bug report.  If the problem still exists,
please respond to this email and we'll reopen the bug report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.