[PATCHv6] system: allow/disallow root login, accept encoded passwords

From: Lorenzo Catucci <lorenzo@sancho.ccd.uniroma2.it>

Currently, there is only two possibilities regarding the root account:
  - it is enabled with no password (the default)
  - it is enabled, using a clear-text, user-provided password

This is deemed insufficient in many cases, especially when the .config
file has to be published (e.g. for the GPL compliance, or any other
reason.).

Fix that in two ways:

  - add a bolean option that allows/disallows root login altogether,
    which defaults to 'y' to keep backward compatibility;

  - accept already-encoded passwords, which we recognise as starting
    with either of $1$, $5$ or $6$ (resp. for md5, sha256 or sha512).

Signed-off-by: Lorenzo M. Catucci <lorenzo@sancho.ccd.uniroma2.it>
[yann.morin.1998@free.fr:
  - don't add a choice to select between clear-text/encoded password,
    use a single prompt;
  - differentiate in the password hook itself;
  - rewrite parts of the help entry;
  - rewrite and expand the commit log
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Tested-by: "Lorenzo M. Catucci" <lorenzo@sancho.ccd.uniroma2.it>

---
Notes:
Lorenzo, I did not add your Acked-by tag, since there was some changes
prompted by Arnout; I however kept your Tested-by since the logic is
still the same. Feel free to review this iteration again. Thanks! :-)

---
Chanages v5 -> v6:
  - use simpler $(filter)  (Arnout)
  - fix default value  (Arnout)
  - expand help about doubling $s  (Arnout)

Changes v4 -> v5:
  - use makefile syntax instead of shell  (Thomas)
  - typoes  (Thomas)
  - fix up the commit log (it never was possible to disable root login)
---
 system/Config.in | 30 +++++++++++++++++++++---------
 system/system.mk | 22 ++++++++++++++++------
 2 files changed, 37 insertions(+), 15 deletions(-)

On 02/05/15 23:30, Yann E. MORIN wrote:
> From: Lorenzo Catucci <lorenzo@sancho.ccd.uniroma2.it>
> 
> Currently, there is only two possibilities regarding the root account:
                   are

>   - it is enabled with no password (the default)
>   - it is enabled, using a clear-text, user-provided password
> 
> This is deemed insufficient in many cases, especially when the .config
> file has to be published (e.g. for the GPL compliance, or any other
> reason.).
> 
> Fix that in two ways:
> 
>   - add a bolean option that allows/disallows root login altogether,
            boolean

>     which defaults to 'y' to keep backward compatibility;
> 
>   - accept already-encoded passwords, which we recognise as starting
>     with either of $1$, $5$ or $6$ (resp. for md5, sha256 or sha512).
> 
> Signed-off-by: Lorenzo M. Catucci <lorenzo@sancho.ccd.uniroma2.it>
> [yann.morin.1998@free.fr:
>   - don't add a choice to select between clear-text/encoded password,
>     use a single prompt;
>   - differentiate in the password hook itself;
>   - rewrite parts of the help entry;
>   - rewrite and expand the commit log
> ]
> Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> Cc: Arnout Vandecappelle <arnout@mind.be>
> Tested-by: "Lorenzo M. Catucci" <lorenzo@sancho.ccd.uniroma2.it>

Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

 A few more optional suggestions below.

> 
> ---
> Notes:
> Lorenzo, I did not add your Acked-by tag, since there was some changes
> prompted by Arnout; I however kept your Tested-by since the logic is
> still the same. Feel free to review this iteration again. Thanks! :-)
> 
> ---
> Chanages v5 -> v6:
>   - use simpler $(filter)  (Arnout)
>   - fix default value  (Arnout)
>   - expand help about doubling $s  (Arnout)
> 
> Changes v4 -> v5:
>   - use makefile syntax instead of shell  (Thomas)
>   - typoes  (Thomas)
>   - fix up the commit log (it never was possible to disable root login)
> ---
>  system/Config.in | 30 +++++++++++++++++++++---------
>  system/system.mk | 22 ++++++++++++++++------
>  2 files changed, 37 insertions(+), 15 deletions(-)
> 
> diff --git a/system/Config.in b/system/Config.in
> index 84cde94..dc46401 100644
> --- a/system/Config.in
> +++ b/system/Config.in
> @@ -176,26 +176,38 @@ endif
>  
>  if BR2_ROOTFS_SKELETON_DEFAULT
>  
> +config BR2_TARGET_ENABLE_ROOT_LOGIN
> +	bool "Enable root login"
> +	default y
> +	help
> +	  Enable root login password

 Perhaps more explicitly: "If not enabled, root login is still possible with
e.g. an authorized ssh key".

> +
>  config BR2_TARGET_GENERIC_ROOT_PASSWD
>  	string "Root password"
>  	default ""
> +	depends on BR2_TARGET_ENABLE_ROOT_LOGIN
>  	help
> -	  Set the initial root password (in clear). It will be md5-encrypted.
> +	  Set the initial root password.
>  
>  	  If set to empty (the default), then no root password will be set,
>  	  and root will need no password to log in.
>  
> -	  WARNING! WARNING!
> -	  Although pretty strong, MD5 is now an old hash function, and
> -	  suffers from some weaknesses, which makes it susceptible to attacks.
> -	  It is showing its age, so this root password should not be trusted
> -	  to properly secure any product that can be shipped to the wide,
> -	  hostile world.
> +	  If the password starts with any of $1$, $5$ or $6$, it is considered
> +	  to be already crypt-encoded with respectively md5, sha256 or sha512.
> +	  Any other value is taken to be a clear-text value, and is crypt-encoded
> +	  as per the "Passwords encoding" scheme, above.
> +
> +	  Note: "$" signs in the hashed password must be doubled. For example,
> +	  if the hashed password is "$1$longsalt$v35DIIeMo4yUfI23yditq0",
> +	  then you must enter it as "$$1$$longsalt$$v35DIIeMo4yUfI23yditq0"
> +	  (this is necessary otherwise make would attempt to interpret the $
> +	  as a variable expansion).
>  
>  	  WARNING! WARNING!
> -	  The password appears in clear in the .config file, and may appear
> +	  The password appears as-is in the .config file, and may appear
>  	  in the build log! Avoid using a valuable password if either the
> -	  .config file or the build log may be distributed!
> +	  .config file or the build log may be distributed, or at the
> +	  very least use a strong cryptographic hash for your password!
>  
>  choice
>  	bool "/bin/sh"
> diff --git a/system/system.mk b/system/system.mk
> index c95e436..53a990b 100644
> --- a/system/system.mk
> +++ b/system/system.mk
> @@ -34,7 +34,7 @@ endef
>  TARGET_FINALIZE_HOOKS += SYSTEM_ISSUE
>  endif
>  
> -ifneq ($(TARGET_GENERIC_ROOT_PASSWD),)
> +ifeq ($(BR2_TARGET_ENABLE_ROOT_LOGIN),y)
>  PACKAGES += host-mkpasswd
>  endif
>  
> @@ -69,12 +69,22 @@ TARGET_FINALIZE_HOOKS += SET_NETWORK
>  
>  ifeq ($(BR2_ROOTFS_SKELETON_DEFAULT),y)
>  
> -define SYSTEM_ROOT_PASSWD
> -	[ -n "$(TARGET_GENERIC_ROOT_PASSWD)" ] && \
> -		TARGET_GENERIC_ROOT_PASSWD_HASH=$$($(MKPASSWD) -m "$(TARGET_GENERIC_PASSWD_METHOD)" "$(TARGET_GENERIC_ROOT_PASSWD)"); \
> -	$(SED) "s,^root:[^:]*:,root:$$TARGET_GENERIC_ROOT_PASSWD_HASH:," $(TARGET_DIR)/etc/shadow
> +ifeq ($(BR2_TARGET_ENABLE_ROOT_LOGIN),y)
> +ifeq ($(TARGET_GENERIC_ROOT_PASSWD),)
> +SYSTEM_ROOT_PASSWORD =
> +else ifneq ($(filter $$1$$% $$5$$% $$6$$%,$(TARGET_GENERIC_ROOT_PASSWD)),)
> +SYSTEM_ROOT_PASSWORD = $(TARGET_GENERIC_ROOT_PASSWD)
> +else

 Perhaps the PACKAGES += host-mkpasswd should move here?

 Perhaps add a comment:

# This variable will only be evaluated in the finalize stage, so we can be sure
# that host-mkpasswd has already been built.


 Regards,
 Arnout

> +SYSTEM_ROOT_PASSWORD = $(shell $(MKPASSWD) -m "$(TARGET_GENERIC_PASSWD_METHOD)" "$(TARGET_GENERIC_ROOT_PASSWD)")
> +endif
> +else # !BR2_TARGET_ENABLE_ROOT_LOGIN
> +SYSTEM_ROOT_PASSWORD = *
> +endif
> +
> +define SYSTEM_SET_ROOT_PASSWD
> +	$(SED) 's,^root:[^:]*:,root:$(SYSTEM_ROOT_PASSWORD):,' $(TARGET_DIR)/etc/shadow
>  endef
> -TARGET_FINALIZE_HOOKS += SYSTEM_ROOT_PASSWD
> +TARGET_FINALIZE_HOOKS += SYSTEM_SET_ROOT_PASSWD
>  
>  ifeq ($(BR2_SYSTEM_BIN_SH_NONE),y)
>  define SYSTEM_BIN_SH
>