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129 lines
9.1 KiB
Markdown
129 lines
9.1 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, when you work with over 1500 profiles, you need a common structure among all the profiles.
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The logic behind it is that if a rule is present in a profile, it should only be in one place, making it easier to review profiles.
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For example, if a program needs to run executable binaries then the rules allowing it can only be in a specific rule block (just after the `@{exec_path} mr,` rule). It 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 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** 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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| Order | Name | Example |
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|:-----:|:----:|:-------:|
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| **1** | [`include`](https://man.archlinux.org/man/apparmor.d.5##include_mechanism) | [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+include+%3Cabstractions%2F&type=code) |
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| **2** | [`set rlimit`](https://man.archlinux.org/man/apparmor.d.5#rlimit_rules) | [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+set+rlimit&type=code) |
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| **3** | [`userns`](https://gitlab.com/apparmor/apparmor/-/wikis/unprivileged_userns_restriction) | [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+userns&type=code) |
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| **4** | [`capability`](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference#capability-rules) | [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+capability&type=code) |
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| **5** | [`network`](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference#network-rules) | [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+%22+network+%22&type=code) |
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| **6** | [`mount`](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference#mount-rules-apparmor-28-and-later) | [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+%22++mount+%22&type=code) |
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| **7** | [`remount`](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference#remount) | [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+remount&type=code) |
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| **8** | [`umount`](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference#umount)| [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+%22umount+%22&type=code) |
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| **9** | [`pivot_root`](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference#pivot_root)| [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+pivot_root&type=code) |
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| **10** | [`change_profile`](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference#change_profile)| [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+change_profile+&type=code) |
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| **11** | `mqueue` | [:octicons-link-external-24:]() |
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| **12** | [`signal`](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference#signals)| [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+%22signal+%22&type=code) |
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| **13** | [`ptrace`](https://man.archlinux.org/man/apparmor.d.5#PTrace_rules) | [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+%22ptrace+%22&type=code) |
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| **14** | [`unix`](https://man.archlinux.org/man/apparmor.d.5#Unix_socket_rules) | [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+%22unix+%22&type=code) |
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| **15** | `io_uring` | [:octicons-link-external-24:]() |
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| **16** | [`dbus`](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference#dbus-rules) | [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md++NOT+path%3A*.go+%22+dbus+%22&type=code) |
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| **17** | [`file`](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference#file-access-rules) | [:octicons-link-external-24:](https://github.com/roddhjav/apparmor.d/blob/2e4788c51ef73798c0ac94993af3cd769723e8e4/apparmor.d/groups/gnome/gnome-shell#L481-L663) |
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| **18** | local include | [:octicons-link-external-24:](https://github.com/search?q=repo%3Aroddhjav%2Fapparmor.d+NOT+path%3A*.md+include+if+exists+%3Clocal&type=code) |
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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 into 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 follows:
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| Order | Description | Example | Link |
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|:-----:|:-----------:|:-------:|:------:|
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| **1** | The entry point of the profile | `@{exec_path} mr,` | [:octicons-link-external-24:](https://github.com/roddhjav/apparmor.d/blob/2e4788c51ef73798c0ac94993af3cd769723e8e4/apparmor.d/groups/gnome/gdm#L67) |
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| **2** | The binaries and library required | `@{bin}/`, `@{lib}/`, `/opt/`. It is the only place where you can have `mr`, `rix`, `rPx`, `rUx`, `rPUX` rules. | [:octicons-link-external-24:](https://github.com/roddhjav/apparmor.d/blob/2e4788c51ef73798c0ac94993af3cd769723e8e4/apparmor.d/groups/gnome/gdm#L69-L76) |
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| **3** | The shared resources | `/usr/share` | [:octicons-link-external-24:](https://github.com/roddhjav/apparmor.d/blob/2e4788c51ef73798c0ac94993af3cd769723e8e4/apparmor.d/groups/network/NetworkManager#L111-L120) |
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| **4** | The system configuration | `/etc` | [:octicons-link-external-24:](https://github.com/roddhjav/apparmor.d/blob/2e4788c51ef73798c0ac94993af3cd769723e8e4/apparmor.d/groups/network/NetworkManager#L111-L120) |
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| **5** | The system data | `/`, `/var`, `/boot` | [:octicons-link-external-24:](https://github.com/roddhjav/apparmor.d/blob/2e4788c51ef73798c0ac94993af3cd769723e8e4/apparmor.d/groups/gnome/tracker-extract#L83-L93) |
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| **6** | The user data | `owner @{HOME}/` | [:octicons-link-external-24:](https://github.com/roddhjav/apparmor.d/blob/2e4788c51ef73798c0ac94993af3cd769723e8e4/apparmor.d/groups/gnome/tracker-extract#L96-L98) |
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| **7** | The user configuration, cache and dotfiles | `@{user_cache_dirs}`, `@{user_config_dirs}`, `@{user_share_dirs}` | [:octicons-link-external-24:](https://github.com/roddhjav/apparmor.d/blob/2e4788c51ef73798c0ac94993af3cd769723e8e4/apparmor.d/groups/browsers/firefox#L179-L202) |
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| **8** | Temporary and runtime data | `/tmp/`, `@{run}/`, `/dev/shm/` | [:octicons-link-external-24:]() |
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| **9** | Sys files | `@{sys}/` | [:octicons-link-external-24:]() |
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| **10** | Proc files | `@{PROC}/` | [:octicons-link-external-24:]() |
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| **11** | Dev files | `/dev/` | [:octicons-link-external-24:]() |
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| **12** | Deny rules | `deny` | [:octicons-link-external-24:]() |
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### The dbus block
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The dbus block should be sorted as follows:
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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-session),
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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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#### :material-numeric-1-circle: Variables
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: Always use the apparmor.d [variables](../variables.md).
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Example:
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- `/usr/lib` or `/usr/bin` become `@{bin}` or `@{lib}`
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- `/usr/sbin` or `/sbin` become `@{bin}`.
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#### :material-numeric-2-circle: Sort
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: In a rule block, all rules must be alphabetically sorted.
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#### :material-numeric-3-circle: Sub-profiles
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: Sub-profiles should come at the end of a profile.
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#### :material-numeric-4-circle: Similar purpose
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: When some rules share similar purposes, they may be sorted together. E.g.:
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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 OpenSUSE Documentation](https://doc.opensuse.org/documentation/leap/security/html/book-security/part-apparmor.html)
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* https://documentation.suse.com/sles/12-SP5/html/SLES-all/cha-apparmor-intro.html
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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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