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163 lines
7.0 KiB
Markdown
163 lines
7.0 KiB
Markdown
## Post install tasks
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### Disk partitions
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#### :information_source: Introduction
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Critical file systems should be separated into different partitions in ways that make your system a better and more secure.
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#### :eight_pointed_black_star: Separate disk partitions
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Make sure the following filesystems are mounted on separate partitions:
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- `/boot`
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- `/tmp`
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- `/var`
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- `/var/log`
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Additionally, depending on the purpose of the server, you should consider separating the following partitions:
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- `/usr`
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- `/home`
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- `/var/www`
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You should also consider separating these partitions:
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- `/var/tmp`
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- `/var/log/audit`
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#### :eight_pointed_black_star: Mount options: nodev, nosuid and noexec
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For more security-focused situations is as follows:
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- `nodev` - specifies that the filesystem cannot contain special devices: This is a security precaution. You don't want a user world-accessible filesystem like this to have the potential for the creation of character devices or access to random device hardware
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- `nosuid` - specifies that the filesystem cannot contain set userid files. Preventing setuid binaries on a world-writable filesystem makes sense because there's a risk of root escalation or other awfulness there
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- `noexec` - this param might be useful for a partition that contains no binaries, like **/var**, or contains binaries you do not want to execute on your system (from partitions with `noexec`), or that cannot even be executed on your system
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#### :eight_pointed_black_star: Secure /boot directory
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The boot directory contains important files related to the Linux kernel, so you need to make sure that this directory is locked down to read-only permissions.
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Add **ro** option and `nodev`, `nosuid` and `noexec` to `/etc/fstab` for **/boot** entry:
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```bash
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LABEL=/boot /boot ext2 defaults,ro,nodev,nosuid,noexec 1 2
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```
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> When updating the kernel you will have to move the flag to `rw`:
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> ```bash
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> mount -o remount,defaults,rw /boot
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> ```
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#### :eight_pointed_black_star: Secure /tmp and /var/tmp
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On Linux systems, the **/tmp** and **/var/tmp** locations are world-writable.
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Several daemons/applications use the **/tmp** or **/var/tmp** directories to temporarily store data, log information, or to share information between their sub-components. However, due to the shared nature of these directories, several attacks are possible, including:
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- Leaks of confidential data via secrets in file names
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- Race-condition attacks (TOCTOU) on the integrity of processes and data
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- Denial-of-Service (DoS) attacks based on race conditions and pre-allocating file/directory names
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As a rule of thumb, malicious applications usually write to **/tmp** and then attempt to run whatever was written. A way to prevent this is to mount **/tmp** on a separate partition with the options `nodev`, `nosuid` and `noexec` enabled.
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This will deny binary execution from **/tmp**, disable any binary to be suid root, and disable any block devices from being created.
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**The first possible scenario is create symlink**
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```bash
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mv /var/tmp /var/tmp.old
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ln -s /tmp /var/tmp
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cp -prf /var/tmp.old/* /tmp && rm -fr /var/tmp.old
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```
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and set properly mount params:
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```bash
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UUID=<...> /tmp ext4 defaults,nodev,nosuid,noexec 1 2
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```
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**The second scenario is a bind mount**
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The storage location **/var/tmp** should be bind mounted to **/tmp**, as having multiple locations for temporary storage is not required:
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```bash
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/tmp /var/tmp none rw,nodev,nosuid,noexec,bind 0 0
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```
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**The third scenario is setting up polyinstantiated directories**
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Create new directories:
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```bash
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mkdir --mode 000 /tmp-inst
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mkdir --mode 000 /var/tmp/tmp-inst
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```
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Edit `/etc/security/namespace.conf`:
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```bash
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/tmp /tmp-inst/ level root,adm
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/var/tmp /var/tmp/tmp-inst/ level root,adm
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```
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Set correct **SELinux** context:
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```bash
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setsebool polyinstantiation_enabled=1
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chcon --reference=/tmp /tmp-inst
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chcon --reference=/var/tmp/ /var/tmp/tmp-inst
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```
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And set `nodev`, `nosuid` and `noexec` mount options in `/etc/fstab`.
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> Alternative for **polyinstantiated directories** is **PrivateTmp** feature available from **systemd**. For more information please see: [New Red Hat Enterprise Linux 7 Security Feature: PrivateTmp](https://access.redhat.com/blogs/766093/posts/1976243).
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#### :eight_pointed_black_star: Secure /dev/shm
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`/dev/shm` is a temporary file storage filesystem, i.e. **tmpfs**, that uses RAM for the backing store. One of the major security issue with the `/dev/shm` is anyone can upload and execute files inside the `/dev/shm` similar to the `/tmp` partition. Further the size should be limited to avoid an attacker filling up this mountpoint to the point where applications could be affected. (normally it allows 20% or more of RAM to be used). The sticky bit should be set like for any world writeable directory.
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For applies to shared memory `/dev/shm` mount params:
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```bash
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tmpfs /dev/shm tmpfs rw,nodev,nosuid,noexec,size=1024M,mode=1777 0 0
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```
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> You can also create a group named 'shm' and put application users for SHM-using applications in there. Then the access can be completely be restricted as such:
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```bash
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tmpfs /dev/shm tmpfs rw,nodev,nosuid,noexec,size=1024M,mode=1770,uid=root,gid=shm 0 0
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```
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#### :eight_pointed_black_star: Secure /proc filesystem
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The proc pseudo-filesystem `/proc` should be mounted with `hidepid`. When setting `hidepid` to **2**, directories entries in `/proc` will hidden.
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```bash
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proc /proc proc defaults,hidepid=2 0 0
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```
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> Some of the services/programs operate incorrectly when the `hidepid` parameter is set, e.g. Nagios checks.
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#### :eight_pointed_black_star: Swap partition
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#### :eight_pointed_black_star: Disk quotas
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#### :ballot_box_with_check: Summary checklist
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| <b>Item</b> | <b>True</b> | <b>False</b> |
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| :--- | :---: | :---: |
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| Separate base partition scheme: `/boot`, `/tmp`, `/var`, `/var/log` | :black_square_button: | :black_square_button: |
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| Separate `/usr` partition | :black_square_button: | :black_square_button: |
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| Separate `/home` partition | :black_square_button: | :black_square_button: |
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| Separate `/var/www` partition | :black_square_button: | :black_square_button: |
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| Separate `/var/tmp` partition | :black_square_button: | :black_square_button: |
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| Separate `/var/audit` partition | :black_square_button: | :black_square_button: |
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| Secure `/boot` directory with `ro`, `nodev`, `nosuid`, `noexec` options | :black_square_button: | :black_square_button: |
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| Secure `/tmp` and `/var/tmp` directory with `nodev`, `nosuid`, `noexec` options | :black_square_button: | :black_square_button: |
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| Create symlink for `/var/tmp` in `/tmp` | :black_square_button: | :black_square_button: |
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| Setting up bind-mount `/var/tmp` to `/tmp` | :black_square_button: | :black_square_button: |
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| Setting up polyinstantiated directories for `/tmp` and `/var/tmp` | :black_square_button: | :black_square_button: |
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| Secure `/dev/shm` directory with `nodev`, `nosuid`, `noexec` options | :black_square_button: | :black_square_button: |
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| Secure `/proc` filesystem with `hidepid=2` option | :black_square_button: | :black_square_button: |
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