mandos-client suppresses NULL characters from passphrases

[Teddy Hogeborn]

"Zen Fu" <zen at torproject.org> writes:

> Hello, Mandos devs!
>
> We're using passphrases randomly generated from /dev/random, and i
> noticed that mandos-client suppresses NULL characters before handing
> the passphrase to stdout. With --debug, the passphrase is printed
> correctly in the output log, but for some reason when printing the
> passphrase to stdout the NULL character is not printed, resulting in
> the wrong passphrase.
>
> I hope this is the correct place to report bugs.

Yes, it is.

> Steps to reproduce:
>
> - generate a passphrase with a NULL character (that's hex 00)
> - use mandos-client to retrieve it
> - see that the passphrase output suppresses the NULL character

I'm sorry to report that I cannot reproduce this.  I can generate a
password containing NUL characters, and it is output correctly by
mandos-client.  I have also reviewed all the code involved in the
copying of the password bytes, and all of the code handles the password
as a buffer of bytes with a length, and never looks at the actual bytes.

I strongly suspect that it's whatever you have reading the password
which is suppressing the NUL character.  I do note that the systemd
Password Agents protocol¹ might be interpreted as implying (but does not
explicitly state) that NUL bytes terminates the password.  Regardless,
when using a systemd-based initramfs image, we do send the entire
password (NUL bytes and all) to the indicated socket (including an
additional terminating NUL byte, as allowed by the protocol), but the
recieving end might do anything.

1. <https://systemd.io/PASSWORD_AGENTS/>

/Teddy Hogeborn

-- 
The Mandos Project
https://www.recompile.se/mandos
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