move selinux, firewalld, k3s

active/software_selinux/selinux.md

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+# Selinux
+
+<https://thecybersecguru.com/tutorials/selinux-ultimate-guide/>
+
+## Terminology
+
+Subjects vs Objects:
+
+- A Subject is a process (e.g., the Apache httpd process).
+- An Object is the thing a subject wants to access (e.g., a file, a directory,
+  a network port, a system socket).
+
+Labels (Contexts):
+
+- Every single Subject and every single Object on an SELinux system has a
+  label. This label is called an SELinux Context.
+- A process’s label is called a domain.
+- A file’s label is called a type.
+
+The Policy:
+
+- The SELinux policy is just a massive database of rules that says which
+  domains can access which types.
+- A rule might say: “Allow the domain httpd_t (the Apache process) to read
+  files with the type httpd_sys_content_t (web content).”
+
+Type Enforcement (TE):
+
+- This is the name of the engine that enforces these rules. When a Subject
+  (process) tries to access an Object (file), the Linux kernel’s hook for
+  SELinux checks their labels.
+- It looks up the rule in the policy.
+- If a rule allow httpd_t httpd_sys_content_t:file { read }; exists, the access
+  is granted.
+- If no “allow” rule exists, the access is implicitly denied, and an event is
+  logged to /var/log/audit/audit.log.
+
+An SELinux context is a string with four parts, separated by colons: `user:role:type:level`
+
+- User: An SELinux user (e.g., system_u, unconfined_u). This is not the same as
+  your Linux user (root, john). It’s an identity within the policy.
+- Role: Used in Role-Based Access Control (RBAC). (e.g., system_r, object_r).
+- Level: Used in Multi-Level Security (MLS) and Multi-Category Security (MCS).
+  (e.g., s0, or s0:c0,c1). This is what keeps containers (Docker, Podman)
+  separate from each other.
+- For 99% of all system administration, you can COMPLETELY IGNORE the user, role, and level.
+
+The only part that matters for day-to-day troubleshooting is the third part:
+the type. This is the real label.
+
+- For a process (Subject), the type is its domain.
+- For a file (Object), the type is its type.
+
+## Using Selinux
+
+```bash
+# List labels
+# The type is the third item in the four colon-separated values
+ls -lZ /var
+ls -lZ /var/log
+ls -lZ .
+
+# List processes
+ps -eZ | grep -i auditd
+ps -eZ | grep -i clam
+ps -eZ | grep -i grep
+```
+
+### Using Selinux Booleans
+
+When you see an "selinux denied" error you have two choices:
+
+1. (Wrong) Write a custom policy module to allow this.
+2. (Right) Check if there’s an “off” switch for this rule.
+
+This “off” switch is called an SELinux Boolean.
+
+Booleans are on/off toggles for common policy rules. They are the first thing
+you should check when you have a denial.
+
+Your workflow should look like:
+
+1. Get a denial.
+2. Run getsebool -a | grep service_name.
+3. Read the list of booleans and find one that sounds like the action being denied.
+4. Temporarily flip it with setsebool.
+5. Test. If it works, make it permanent with setsebool -P.
+
+```bash
+# Get all booleans
+getsebool -a
+
+# Find one that's relevant
+getsebool -a | grep -i clam
+
+# Flip an sebool on temporarily
+setsebool httpd_can_network_connect_db on
+
+# Flip sebool on permanently
+setsebool -P httpd_can_network_connect_db on
+```
+
+### Using Selinux with Audit Log
+
+If the selinux boolean approach doesn't work.
+
+```bash
+# Make sure you have the troubleshooting package installed
+sudo dnf install -y setroubleshoot-server
+
+# List all alerts
+sudo sealert -a /var/log/audit/audit.log
+
+# If sealert doesn't have a recommendation, like restorecon, then use audit2why
+# This will tell you what you should do to fix the issue
+sudo grep "denied" /var/log/audit/audit.log | tail -n 1 | audit2why
+
+# Check what rule would be created
+sudo grep "antivirus_t" /var/log/audit/audit.log | audit2allow -m clamav-notifysend
+
+# Create the .te (human readable) policy, compile it (.pp), and load it into the kernel
+sudo grep "antivirus_t" /var/log/audit/audit.log | audit2allow -M clamav-notifysend
+
+# Apply the policy
+sudo semodule -X 300 -i clamav-notifysend.pp
+
+# List active policies
+sudo semodule -l
+
+# Remove an active policy
+sudo semodule -r clamav-notifysend
+```
+
+### Showing Dontaudit Rules
+
+Selinux will hide denies that are explicitly prohibited through a rule.
+
+```bash
+# Show dontaudit rules
+semodule -DB
+
+# Hide dontaudit rules
+semodule -B
+```
+
+## Compiling Modules
+
+If you have a `te` file you can compile to a `pp` file with the following:
+
+```bash
+# Compile to module source, then to policy package
+checkmodule -M -m -o sample.mod sample.te
+semodule_package -o sample.pp -m sample.mod
+```
+
+## Cloning a Virtual Machine
+
+```bash
+cd active/os_fedora/selinux_policies
+sudo ausearch -c 'rpc-virtstorage' --raw | audit2allow -M my-rpcvirtstorage
+sudo semodule -X 300 -i my-rpcvirtstorage.pp
+```