Difference between revisions of "Security (Buster)"
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== PAM == | == PAM == | ||
| − | # Install the libpam-tmpdir package, if you have not already. | + | # Be sure you have the wheel group: addgroup --gid 70 wheel |
| + | # usermod -a -G wheel root | ||
| + | # usermod -a -G wheel adminuser | ||
| + | # Install the libpam-tmpdir package, if you have not already (lately has been autoinstalled). | ||
# /etc/pam.d/common-auth | # /etc/pam.d/common-auth | ||
## Remove nullok_secure from the auth line | ## Remove nullok_secure from the auth line | ||
Revision as of 19:30, 21 January 2021
Security is a process, not a state. On the plus side, a lot of stuff from my earlier documentation on this has become the default in Wheezy. It is certainly made easier by not being the only one doing it.
Not all of this is strictly 'security', per se, at least from a 'keep bad people from doing bad things to you' perspective. Some elements are more about ensuring a smoother-running system.
/etc/fstab
# <file system> <mount point> <type> <options> <dump> <pass> # / was on /dev/sda3 during installation UUID=longstringissomewhatlongbutnotverylong / ext4 noatime,errors=remount-ro 0 1 # /boot was on /dev/sda1 during installation UUID=longstringissomewhatlongbutnotverylong /boot ext4 noatime 0 2 # /home was on /dev/sda2 during installation UUID=longstringissomewhatlongbutnotverylong /home ext4 noatime,nodev,nosuid 0 2 # /innodb was on /dev/sdd1 during installation UUID=longstringissomewhatlongbutnotverylong /innodb ext4 noatime,nodev,nosuid,noexec 0 2 # /srv was on /dev/sdc1 during installation UUID=longstringissomewhatlongbutnotverylong /srv ext4 noatime,nodev,nosuid,noexec 0 2 # /storage was on /dev/sdd2 during installation UUID=longstringissomewhatlongbutnotverylong /storage ext4 noatime,nodev,nosuid,noexec 0 2 # /var was on /dev/sdb2 during installation UUID=longstringissomewhatlongbutnotverylong /var ext4 noatime,nodev,nosuid 0 2 # swap was on /dev/sdb1 during installation UUID=longstringissomewhatlongbutnotverylong none swap sw 0 0 tmpfs /tmp tmpfs rw,noatime,nodev,nosuid,mode=1777,size=8g 0 0
The main thing here is the tmpfs and nodev,nosuid /tmp.
/boot is a silly thing to stick on its own partition these days, it's just habit, and can actually causes more headache than the benefit it supposedly provided. Necessary if you encrypt your root partition, however.
noatime goes on all the things, except the swap partition.
Speaking of swap partitions, they are still useful, but I would not make them too large. I generally set it to about 4gb, and with the configuration I have described, between half a gig and a gig may end up being used without impacting performance - there is a bit of room your server can squeeze out to generally make good use of the RAM inside.
nodev, nosuid is good for anything that doesn't need those abilities - / and /boot.
Be careful about throwing noexec around. Debian likes to execute some things out of /var and /tmp.
/innodb is a partition that holds nothing but InnoDB's double buffer and other logs. Since it represents half of an InnoDB database's I/O, this ends up being about 40% faster than an equivalent RAID 0 or 10 configuration.
To enable fstrim properly, you will want to enable the timer service:
systemctl enable fstrim.timer
And make an override to switch it to daily:
mkdir /etc/systemd/system/fstrim.timer.d touch /etc/systemd/system/fstrim.timer.d/override.conf
- /etc/systemd/system/fstrim.timer.d/override.conf
[Timer] OnCalendar= OnCalendar=daily
The double declarations are intentional, to first delete the previously set OnCalendar value.
/etc/crontab
# /etc/crontab: system-wide crontab # Your values may of course differ. I just prefer to spread them out # So they don't all hit at the same time usually. # Key is to know when your user activity is the lowest, of course.
SHELL=/bin/sh PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin MAILTO=""
17 * * * * root cd / && run-parts --report /etc/cron.hourly 25 6 * * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily ) 47 5 * * 7 root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly ) 52 4 1 * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly ) #
/etc/securetty
# /etc/securetty: list of terminals on which root is allowed to login. # See securetty(5) and login(1). # I end up deleting the vast majority of these, leaving only the ones below.
console
# Virtual consoles tty1 tty2 tty3 tty4 tty5 tty6 tty7 tty8 tty9 tty10 tty11 tty12
/etc/security/limits.conf
#<domain> <type> <item> <value> # The main thing to note here are the core dumps # and mysql's memory access. The latter is a # legacy element. # * soft core 0 * hard core - * - maxlogins 5 * - memlock 2048 * - nofile 65536 * - nproc 256 mysql - maxlogins 0 mysql - memlock 134217728 mysql - nofile 1048576 root - nofile - root - maxlogins - root - memlock 134217728 root - nproc -
/etc/host.conf
Read hosts first, then try a domain lookup if that fails. I am far more likely to be trying to override something when I put something in my hosts file.
This file is largely obsolete.
order hosts,bind multi on
/etc/login.defs
- LOG_OK_LOGINS yes
- SULOG_FILE /var/log/sulog
- CHFN_RESTRICT frwh
- Don't ask me why I bother with this, I could not tell you : p
- SHA_CRYPT_MIN_ROUNDS 500000
- Or higher. Just remember what you are setting it to.
PAM
- Be sure you have the wheel group: addgroup --gid 70 wheel
- usermod -a -G wheel root
- usermod -a -G wheel adminuser
- Install the libpam-tmpdir package, if you have not already (lately has been autoinstalled).
- /etc/pam.d/common-auth
- Remove nullok_secure from the auth line
- /etc/pam.d/su
- Uncomment and add group=wheel:
- auth required pam_wheel.so group=wheel
- Make sure root is part of the wheel group as precaution
- /etc/pam.d/common-password
- add 'rounds=65536' to the password line:
- password [success=1 default=ignore] pam_unix.so obscure sha512 rounds=65536
- Regenerate root, administrator passwords
Directory and file Permissions
find / -perm -2000 -group 0
This should only return directories. /var/cache/man in particular.
chmod 0700 /root /lost+found
The above should already be the case.
chmod 0751 /etc /home /etc/ssh/ chmod 0750 /mnt /boot /etc/rsyslog.d/ /etc/cron.d/ /etc/cron.hourly/ /etc/cron.daily/ /etc/cron.weekly/ /etc/cron.monthly/ chmod 0750 /storage /innodb
Or whatever you choose your database/general directories to be. I dislike /opt and /srv, at least for things that I will be dedicating entire hard drives to (or most of them).
chgrp staff /storage
Or whatever again.
chmod 0640 /etc/crontab /etc/fstab /etc/securetty /etc/ssh/sshd_config /etc/rsyslog.conf
Clear out unnecessary setuid binaries:
find / -perm -4000 -user 0
Only /bin/su is absolutely necessary.
- /sbin/pam-tmpdir-helper is needed if you are using the pam tmpdir module above
- /usr/lib/dbus-1.0/dbus-daemon-launch-helper is needed by dbus which systemd requires.
- suexec if you are still using Apache
- sudo if you use that. Since this is a server, I find the idea of typing 'sudo' before a million commands highly annoying, personally. That said it is still useful for launching processes as a separate user for various tasks.
On a default Wheezy install:
chmod u-s /usr/bin/passwd /usr/bin/chsh /usr/bin/gpasswd /usr/bin/newgrp /usr/bin/chfn /usr/lib/eject/dmcrypt-get-device /usr/lib/openssh/ssh-keysign /bin/mount /bin/umount
No reason for anyone to be running any of these on a server.
chmod u-s /sbin/mount.nfs
If using nfs
Remove sound support
This is less security and more of a misc issue. Still, my server is in a secure building thousands of miles away, it shouldn't be making noise I can hear.
To get sound modules:
lsmod | grep snd lsmod | grep sound lsmod | grep spkr
Blacklist these, along with pcspkr, in a file like /etc/modprobe.d/blacklist.conf:
# /etc/modprobe.d/sound-blacklist.conf # Hear no evil. blacklist pcspkr blacklist snd_pcm blacklist snd_timer blacklist snd_page_alloc blacklist snd blacklist snd-pcsp blacklist soundcore