[Buildroot] Proposed patch: allow setting an hashed root password

[Yann E. MORIN <yann.morin.1998@free.fr>]

Johan, All,

On 2015-03-23 12:05 +0100, Johan Oudinet spake thusly:
> On Sun, Mar 22, 2015 at 11:56 PM, Yann E. MORIN <yann.morin.1998@free.fr> wrote:
> >
> > Alternatively, you could also tweak the root password from a post-build
> > script, see BR2_ROOTFS_POST_BUILD_SCRIPT:
> >     http://buildroot.net/downloads/manual/manual.html#rootfs-custom
> >
> > script which could look something like:
> >
> >     #!/bin/sh
> >     PASSWD='your-encoded-password'
> >     sed -r -i -e "s/^root:[^:]+:/root:${PASSWD}:/" "${TARGET_DIR}/etc/passwd"
> >
> > And in the end, I wonder if that would not be the best option...
> >
> 
> This is the solution we do internally. I'm not sure how hard it is for
> us to send it upstream as it implies several changes. I'll look into
> it this week.
> Basically, we have a script to ease the access to BR2_* variables
> inside post_build scripts, then we have a post_build script that looks
> to BR2_TARGET_GENERIC_ROOT_PASSWD and:
> - if it's empty, it does nothing;
> - if it starts by $1$, $5$, or $6$, it assumes it is already
> encrypted, and skip the encoding part
> - otherwise, first it encodes it by calling mkpasswd with the
> BR2_TARGET_GENERIC_PASSWD_METHOD method, then it replaces the second
> field of the root user in the /etc/shadow file

Well, recognising an md5, sha256 or sha512 hashed password from a
plain-text one is pretty trivial.

What's not so trivial is recognising:
  - a DES-encoded password
  - a disabled password, marked with a leading '!'
  - a no-login password, marked with just a single '*'

Detecting a DES-encoded password is not easy because the accepted chars
are in a sub-set as those accepted for a plain-text password.

However, maybe we could deprecate DES-encoding altogether, then we
could handle those cases:

  - password is '*'                 --> login not allowed; stop
  - password starts with '!'        --> login disabled, skip the '!'; continue
  - password starts with ${1,5,6}$  --> treat it as an encoded password; stop
  - anything else                   --> treat it as a plain-text password

That way, the existing option can be re-used for all cases, and we would
not need anything more, just adapting the current code in system/system.mk.

Thoughts?

Regards,
Yann E. MORIN.

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