CODEWITHSUNDEEP
linuxssh
Curt
Curt

Reputation: 1414

Why does SSH_ASKPASS not work with a c program?

I was wondering about using SSH_ASKPASS to initiate an SSH session from a script, and so I wrote a script like this:

export SSH_ASKPASS="/path/passwordScript"
setsid ssh "username"@"host"

where passwordScript is a bash script that echoes the user's password like this:

#!/usr/bin/env bash
echo "the_password"

Where "the_password" is the user's password. This process worked fine, and the SSH session connected successfully.

Out of curiosity, I tried to change passwordScript to a c script like this (obviously this is the uncompiled version):

#include <stdio.h>

main()
{
    printf("the_password\n");
}

To my surprise, the SSH session would no longer connect. The output looks like this:

Permission denied, please try again.
Permission denied, please try again.
Permission denied (publickey,gssapi-with-mic,password).

I thought perhaps the bash interpreter wasn't actually being used, and sh was being used by default or something. However, the SSH session works fine if I setup passwordScript in python like this:

#!/usr/bin/env python
print "the_password"

So my question is why doesn't ASK_PASS work with my c program?

(As an aside, I know that SSH keys are better suited for this situation; this was just a learning exercise)

Thanks!

Upvotes: 1

Views: 693

Answers (1)

Curt
Curt

Reputation: 1414

My guess is that SSH_ASKPASS checks the return code. If I modify the c program to have return code 0 everything works as expected:

#include <stdio.h>

int main ()
{
    printf("the_password");
    return 0;
}

Upvotes: 2

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