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129 lines
3.6 KiB
Markdown
129 lines
3.6 KiB
Markdown
---
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title: Guidelines
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---
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## Common structure
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AppArmor profiles can be written without any specific guidelines. However,
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when you work with over 1400 profiles, you need a common structure among all the
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profiles.
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The logic behind it is that if a rule is present in a profile, it should only be
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in one place, making profile review easier.
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For example, if a program needs to run executables binary. The rules allowing it
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can only be in a specific rule block (just after the `@{exec_path} mr,` rule). It
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is therefore easy to ensure some profile features such as:
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* A profile has access to a given resource
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* A profile enforces a strict [write xor execute] (W^X) policy.
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It also improves compatibilities and makes personalization easier thanks to the
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use of more variables.
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## Guidelines
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!!! note
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This profile guideline is still evolving, feel free to propose improvements
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as long as they do not vary too much from the existing rules.
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In order to ensure a common structure across the profiles, all new profile **must**
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follow the guidelines presented here.
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The rules in the profile should be sorted in the rule ***block*** as follows:
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- `include`
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- `set rlimit`
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- `capability`
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- `network`
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- `mount`
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- `remount`
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- `umount`
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- `pivot_root`
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- `change_profile`
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- `signal`
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- `ptrace`
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- `unix`
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- `dbus`
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- `file`
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- local include
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This rule order is taken from AppArmor with minor changes as we tend to:
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- Divide the file block in multiple subcategories
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- Put the block with the longer rules (`files`, `dbus`) after the other blocks
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### The file block
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The file block should be sorted as follow:
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- `@{exec_path} mr`, the entry point of the profile
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- The binaries and library required:
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- `/{usr/,}bin/`, `/{usr/,}lib/`, `/opt/`...
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- It is the only place where you can have `mr`, `rix`, `rPx`, `rUx`, `rPUX` rules.
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- The shared resources: `/usr/share`...
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- The system configuration: `/etc`...
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- The system data: `/var`...
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- The user data: `owner @{HOME}/`...
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- The user configuration, cache and in general all dotfiles
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- Temporary and runtime data: `/tmp/`, `@{run}/`, `/dev/shm/`...
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- Sys files: `@{sys}/`...
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- Proc files: `@{PROC}/`...
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- Dev files: `/dev/`...
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- Deny rules: `deny`...
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### The dbus block
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The dbus block should be sorted as follow:
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- The system bus should be sorted *before* the session bus
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- The bind rules should be sorted *after* the send & receive rules
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For DBus, try to determine peer's label when possible. E.g.:
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```
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dbus send bus=session path=/org/freedesktop/DBus
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interface=org.freedesktop.DBus
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member={RequestName,ReleaseName}
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peer=(name=org.freedesktop.DBus, label=dbus-daemon),
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```
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If there is no predictable label it can be omitted.
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### Profile rules
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`bin, sbin & lib`
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: - Do not use: `/usr/lib` or `/usr/bin` but `/{usr/,}bin/` or `/{usr/,}lib/`
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- Do not use: `/usr/sbin` or `/sbin` but `/{usr/,}{s,}bin/`.
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`Variables`
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: Always use the apparmor variables.
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`Sort`
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: In a rule block, the rules must be alphabetically sorted.
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`Sub profile`
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: Sub profile should comes at the end of a profile.
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`Similar purpose`
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: When some rules share similar purpose, they may be sorted together. Eg:
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```
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/etc/machine-id r,
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/var/lib/dbus/machine-id r,
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```
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## Additional recommended documentation
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* [The AppArmor Core Policy Reference](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference)
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* [The AppArmor.d man page](https://man.archlinux.org/man/apparmor.d.5)
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* [F**k AppArmor](https://presentations.nordisch.org/apparmor/#/)
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* [A Brief Tour of Linux Security Modules](https://www.starlab.io/blog/a-brief-tour-of-linux-security-modules)
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[write xor execute]: https://en.wikipedia.org/wiki/W%5EX
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