bug#56336: 28.1.90; [28.1] Emacs prompts for password when output from async command contains "password:"

bug#56336: 28.1.90; [28.1] Emacs prompts for password when output from async command contains "password:"

[Jan Synáček]

When the output from a command spawned with 'M-&' (async-shell-command)
ends with "password:" Emacs prompts for a password.

Reproducer:
0) $ cat /tmp/test.txt
   enter your password:
1) emacs -Q
2) Press 'M-&', enter 'cat /tmp/test.txt' as input and hit enter.
3) Emacs prompts for a password.

I expect that 3) should not happen as the output is simply to stdout and
no stdin input is expected. Note that the reproducer is minimal and a
bit contrived but the real bug showed itself when I was running a big
test suite that contained several lines ending with "password:" in its
output.

I've also tested this with the latest master (commit
3a4c408a7b6f3df5ca0eb4a406efbdb4899e9742), where it sometimes happens as
well and sometimes you just get an error like this:

Error running timer: (error "Buffer *Async Shell Command* has no process")


In GNU Emacs 28.1.90 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.34, cairo version 1.17.6)
 of 2022-07-01 built on jsynacek-home
Repository revision: 7e33618bbc07b65c36744db8e7ef219d2d942456
Repository branch: emacs-28
Windowing system distributor 'The X.Org Foundation', version 11.0.12101003
System Description: Arch Linux

Configured using:
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bug#56336: 28.1.90; [28.1] Emacs prompts for password when output from async command contains "password:"

[Lars Ingebrigtsen]

Jan Synáček <jan.synacek@gmail.com> writes:

> When the output from a command spawned with 'M-&' (async-shell-command)
> ends with "password:" Emacs prompts for a password.
>
> Reproducer:
> 0) $ cat /tmp/test.txt
>    enter your password:
> 1) emacs -Q
> 2) Press 'M-&', enter 'cat /tmp/test.txt' as input and hit enter.
> 3) Emacs prompts for a password.
>
> I expect that 3) should not happen as the output is simply to stdout and
> no stdin input is expected. Note that the reproducer is minimal and a
> bit contrived but the real bug showed itself when I was running a big
> test suite that contained several lines ending with "password:" in its
> output.
>
> I've also tested this with the latest master (commit
> 3a4c408a7b6f3df5ca0eb4a406efbdb4899e9742), where it sometimes happens as
> well and sometimes you just get an error like this:
>
> Error running timer: (error "Buffer *Async Shell Command* has no process")

I've now fixed the latter in Emacs 29.

The former problem is rather intractable.  That is, if you say

ssh foo@host

you'll get a password prompt as the final line in the buffer, and Emacs
will ask you to enter a password.

If you say

echo -n "password: "; sleep 10; echo foo

then there's no way for Emacs to distinguish that from the ssh
situation: It sees a prompt as the last thing in the buffer, and Emacs
can't possibly know that that's not a process asking for a password.

Note that

echo "password: "; echo foo; sleep 10

won't ask for a password.

So I don't know that there's any way to fix this -- Emacs uses a
heuristic, and it will be wrong in some cases.

Or does anybody have any ideas here?

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

bug#56336: 28.1.90; [28.1] Emacs prompts for password when output from async command contains "password:"

[miha--- via Bug reports for GNU Emacs, the Swiss army knife of text editors]

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Lars Ingebrigtsen <larsi@gnus.org> writes:

> I've now fixed the latter in Emacs 29.

Thanks. I think an equivalent change could be made for
eshell-watch-for-password-prompt and term-watch-for-password-prompt as
well.

Best regards.

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bug#56336: 28.1.90; [28.1] Emacs prompts for password when output from async command contains "password:"

[Lars Ingebrigtsen]

miha@kamnitnik.top writes:

> Thanks. I think an equivalent change could be made for
> eshell-watch-for-password-prompt and term-watch-for-password-prompt as
> well.

Are they used in contexts where this is meaningful?  I.e., used from
commands like `M-&' that kill off the shell?

But I guess for resilience it doesn't hurt...

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

bug#56336: 28.1.90; [28.1] Emacs prompts for password when output from async command contains "password:"

[Jan Synáček]

On Sat, Jul 2, 2022 at 2:28 PM Lars Ingebrigtsen <larsi@gnus.org> wrote:
> The former problem is rather intractable.  That is, if you say
>
> ssh foo@host
>
> you'll get a password prompt as the final line in the buffer, and Emacs
> will ask you to enter a password.
>
> If you say
>
> echo -n "password: "; sleep 10; echo foo
>
> then there's no way for Emacs to distinguish that from the ssh
> situation: It sees a prompt as the last thing in the buffer, and Emacs
> can't possibly know that that's not a process asking for a password.
>
> Note that
>
> echo "password: "; echo foo; sleep 10
>
> won't ask for a password.
>
> So I don't know that there's any way to fix this -- Emacs uses a
> heuristic, and it will be wrong in some cases.
>
> Or does anybody have any ideas here?

Well, I know about one thing that might work well enough as an
additional heuristic just for this case.

It seems that if a command only outputs to stdout (and probably to
stderr as well) and doesn't really ask for input, lsof -p <that async
process> shows something like this:
$ lsof -p 145475
...
sleep   145475 jsynacek    0u   CHR  136,1      0t0        4 /dev/pts/1
sleep   145475 jsynacek    1u   CHR  136,1      0t0        4 /dev/pts/1
sleep   145475 jsynacek    2u   CHR  136,1      0t0        4 /dev/pts/1

Whereas if the command really wants input ('ssh jsynacek@localhost' in
this particular example), it looks like the following:
$ lsof -p 145512
...
ssh     145512 jsynacek    0u   CHR              136,1      0t0
4 /dev/pts/1
ssh     145512 jsynacek    1u   CHR              136,1      0t0
4 /dev/pts/1
ssh     145512 jsynacek    2u   CHR              136,1      0t0
4 /dev/pts/1
ssh     145512 jsynacek    3u  IPv6             203802      0t0
TCP localhost:32864->localhost:ssh (ESTABLISHED)
ssh     145512 jsynacek    4u  unix 0x000000006034f025      0t0
203803 type=STREAM (CONNECTED)
ssh     145512 jsynacek    5u   CHR                5,0      0t0
11 /dev/tty

Note the /dev/tty in the output. I'm not sure, but I think this might
be good enough.

-- 
Jan Synáček

bug#56336: 28.1.90; [28.1] Emacs prompts for password when output from async command contains "password:"

[Lars Ingebrigtsen]

Jan Synáček <jan.synacek@gmail.com> writes:

> Well, I know about one thing that might work well enough as an
> additional heuristic just for this case.
>
> It seems that if a command only outputs to stdout (and probably to
> stderr as well) and doesn't really ask for input, lsof -p <that async
> process> shows something like this:
> $ lsof -p 145475

[...]

> Note the /dev/tty in the output. I'm not sure, but I think this might
> be good enough.

It's not portable across operating systems, though.  (And the processes
may play shenanigans with detaching and spawning other processes that
then ask for a password (think xdg-open and friends), so it's not
reliable on Linux either.)

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

bug#56336: 28.1.90; [28.1] Emacs prompts for password when output from async command contains "password:"

[Lars Ingebrigtsen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

>> Thanks. I think an equivalent change could be made for
>> eshell-watch-for-password-prompt and term-watch-for-password-prompt as
>> well.
>
> Are they used in contexts where this is meaningful?  I.e., used from
> commands like `M-&' that kill off the shell?

There wasn't any followup here in a month, so I don't think it's worth
tweaking this more unless anybody has an actual case where this bugs
out, and I'm therefore closing this bug report.