Linux From Scratch (w/Pacman) - Version r12.3-6-wip

Chapter 7. Entering Chroot and Building Additional Temporary Tools

7.38. Shadow-4.17.3

The Shadow package contains programs for handling passwords in a secure way.

Approximate build time: 0.1 SBU
Required disk space: 114 MB

7.38.1. Installation of Shadow

Disable the installation of the groups program and its man pages, as Coreutils provides a better version. Also, prevent the installation of manual pages that will be installed in Section 8.4, “Man-pages-6.13”: 

sed -i 's/groups$(EXEEXT) //' src/Makefile.in
find man -name Makefile.in -exec sed -i 's/groups\.1 / /'   {} \;
find man -name Makefile.in -exec sed -i 's/getspnam\.3 / /' {} \;
find man -name Makefile.in -exec sed -i 's/passwd\.5 / /'   {} \;

Instead of using the default crypt method, use the much more secure YESCRYPT method of password encryption, which also allows passwords longer than 8 characters. It is also necessary to change the obsolete /var/spool/mail location for user mailboxes that Shadow uses by default to the /var/mail location used currently. And, remove /bin and /sbin from the PATH, since they are simply symlinks to their counterparts in /usr.

[Warning]

Warning

Including /bin and/or /sbin in the PATH variable may cause some BLFS packages fail to build, so don't do that in the .bashrc file or anywhere else. 

sed -e 's:#ENCRYPT_METHOD DES:ENCRYPT_METHOD YESCRYPT:' \
    -e 's:/var/spool/mail:/var/mail:'                   \
    -e '/PATH=/{s@/sbin:@@;s@/bin:@@}'                  \
    -i etc/login.defs

Prepare Shadow for compilation: 

touch /usr/bin/passwd
./configure --sysconfdir=/etc   \
            --disable-static    \
            --with-{b,yes}crypt \
            --without-libbsd    \
            --with-group-name-max-length=32

The meaning of the new configuration options:

touch /usr/bin/passwd

The file /usr/bin/passwd needs to exist because its location is hardcoded in some programs; if it does not already exist, the installation script will create it in the wrong place.

--with-{b,yes}crypt

The shell expands this to two switches, --with-bcrypt and --with-yescrypt. They allow shadow to use the Bcrypt and Yescrypt algorithms implemented by Libxcrypt for hashing passwords. These algorithms are more secure (in particular, much more resistant to GPU-based attacks) than the traditional SHA algorithms.

--with-group-name-max-length=32

The longest permissible user name is 32 characters. Make the maximum length of a group name the same.

--without-libbsd

Do not use the readpassphrase function from libbsd which is not in LFS. Use the internal copy instead.

Compile the package: 

make

This package does not come with a test suite.

Install the package: 

make exec_prefix=/usr install

7.38.2. Configuring Shadow

This package contains utilities to add, modify, and delete users and groups; set and change their passwords; and perform other administrative tasks. For a full explanation of what password shadowing means, see the doc/HOWTO file within the unpacked source tree. If you use Shadow support, keep in mind that programs which need to verify passwords (display managers, FTP programs, pop3 daemons, etc.) must be Shadow-compliant. That is, they must be able to work with shadowed passwords.

To enable shadowed passwords, run the following command: 

pwconv

To enable shadowed group passwords, run: 

grpconv

Shadow's default configuration for the useradd utility needs some explanation. First, the default action for the useradd utility is to create the user and a group with the same name as the user. By default the user ID (UID) and group ID (GID) numbers will begin at 1000. This means if you don't pass extra parameters to useradd, each user will be a member of a unique group on the system. If this behavior is undesirable, you'll need to pass either the -g or -N parameter to useradd, or else change the setting of USERGROUPS_ENAB in /etc/login.defs. See useradd(8) for more information.

Second, to change the default parameters, the file /etc/default/useradd must be created and tailored to suit your particular needs. Create it with: 

mkdir -p /etc/default
useradd -D --gid 999

/etc/default/useradd parameter explanations

GROUP=999

This parameter sets the beginning of the group numbers used in the /etc/group file. The particular value 999 comes from the --gid parameter above. You may set it to any desired value. Note that useradd will never reuse a UID or GID. If the number identified in this parameter is used, it will use the next available number. Note also that if you don't have a group with an ID equal to this number on your system, then the first time you use useradd without the -g parameter, an error message will be generated—useradd: unknown GID 999, even though the account has been created correctly. That is why we created the group users with this group ID in Section 7.6, “Creating Essential Files and Symlinks.”

CREATE_MAIL_SPOOL=yes

This parameter causes useradd to create a mailbox file for each new user. useradd will assign the group ownership of this file to the mail group with 0660 permissions. If you would rather not create these files, issue the following command: 

sed -i '/MAIL/s/yes/no/' /etc/default/useradd