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115 lines
8.2 KiB
Markdown
115 lines
8.2 KiB
Markdown
# CGroup Namespace
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<details>
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<summary><strong>HackTricks in</strong> <a href="https://twitter.com/carlospolopm"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch</strong></a> <strong>Wed - 18.30(UTC) 🎙️</strong> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
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* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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## Basic Information
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A cgroup namespace is a Linux kernel feature that provides **isolation of cgroup hierarchies for processes running within a namespace**. Cgroups, short for **control groups**, are a kernel feature that allows organizing processes into hierarchical groups to manage and enforce **limits on system resources** like CPU, memory, and I/O.
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While cgroup namespaces are not a separate namespace type like the others we discussed earlier (PID, mount, network, etc.), they are related to the concept of namespace isolation. **Cgroup namespaces virtualize the view of the cgroup hierarchy**, so that processes running within a cgroup namespace have a different view of the hierarchy compared to processes running in the host or other namespaces.
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### How it works:
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1. When a new cgroup namespace is created, **it starts with a view of the cgroup hierarchy based on the cgroup of the creating process**. This means that processes running in the new cgroup namespace will only see a subset of the entire cgroup hierarchy, limited to the cgroup subtree rooted at the creating process's cgroup.
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2. Processes within a cgroup namespace will **see their own cgroup as the root of the hierarchy**. This means that, from the perspective of processes inside the namespace, their own cgroup appears as the root, and they cannot see or access cgroups outside of their own subtree.
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3. Cgroup namespaces do not directly provide isolation of resources; **they only provide isolation of the cgroup hierarchy view**. **Resource control and isolation are still enforced by the cgroup** subsystems (e.g., cpu, memory, etc.) themselves.
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For more information about CGroups check:
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{% content-ref url="../cgroups.md" %}
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[cgroups.md](../cgroups.md)
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{% endcontent-ref %}
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## Lab:
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### Create different Namespaces
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#### CLI
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```bash
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sudo unshare -C [--mount-proc] /bin/bash
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```
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By mounting a new instance of the `/proc` filesystem if you use the param `--mount-proc`, you ensure that the new mount namespace has an **accurate and isolated view of the process information specific to that namespace**.
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<details>
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<summary>Error: bash: fork: Cannot allocate memory</summary>
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If you run the previous line without `-f` you will get that error.\
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The error is caused by the PID 1 process exits in the new namespace.
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After bash start to run, bash will fork several new sub-processes to do somethings. If you run unshare without -f, bash will have the same pid as the current "unshare" process. The current "unshare" process call the unshare systemcall, create a new pid namespace, but the current "unshare" process is not in the new pid namespace. It is the desired behavior of linux kernel: process A creates a new namespace, the process A itself won't be put into the new namespace, only the sub-processes of process A will be put into the new namespace. So when you run:
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```
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unshare -p /bin/bash
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```
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The unshare process will exec /bin/bash, and /bin/bash forks several sub-processes, the first sub-process of bash will become PID 1 of the new namespace, and the subprocess will exit after it completes its job. So the PID 1 of the new namespace exits.
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The PID 1 process has a special function: it should become all the orphan processes' parent process. If PID 1 process in the root namespace exits, kernel will panic. If PID 1 process in a sub namespace exits, linux kernel will call the disable\_pid\_allocation function, which will clean the PIDNS\_HASH\_ADDING flag in that namespace. When linux kernel create a new process, kernel will call alloc\_pid function to allocate a PID in a namespace, and if the PIDNS\_HASH\_ADDING flag is not set, alloc\_pid function will return a -ENOMEM error. That's why you got the "Cannot allocate memory" error.
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You can resolve this issue by use the '-f' option:
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```
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unshare -fp /bin/bash
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```
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If you run unshare with '-f' option, unshare will fork a new process after it create the new pid namespace. And run /bin/bash in the new process. The new process will be the pid 1 of the new pid namespace. Then bash will also fork several sub-processes to do some jobs. As bash itself is the pid 1 of the new pid namespace, its sub-processes can exit without any problem.
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Copied from [https://stackoverflow.com/questions/44666700/unshare-pid-bin-bash-fork-cannot-allocate-memory](https://stackoverflow.com/questions/44666700/unshare-pid-bin-bash-fork-cannot-allocate-memory)
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</details>
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#### Docker
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```bash
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docker run -ti --name ubuntu1 -v /usr:/ubuntu1 ubuntu bash
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```
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###  Check which namespace is your process in
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```bash
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ls -l /proc/self/ns/cgroup
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lrwxrwxrwx 1 root root 0 Apr 4 21:19 /proc/self/ns/cgroup -> 'cgroup:[4026531835]'
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```
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### Find all CGroup namespaces
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{% code overflow="wrap" %}
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```bash
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sudo find /proc -maxdepth 3 -type l -name cgroup -exec readlink {} \; 2>/dev/null | sort -u
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# Find the processes with an specific namespace
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sudo find /proc -maxdepth 3 -type l -name cgroup -exec ls -l {} \; 2>/dev/null | grep <ns-number>
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```
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{% endcode %}
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### Enter inside an CGroup namespace
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```bash
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nsenter -C TARGET_PID --pid /bin/bash
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```
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Also, you can only **enter in another process namespace if you are root**. And you **cannot** **enter** in other namespace **without a descriptor** pointing to it (like `/proc/self/ns/cgroup`).
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<details>
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<summary><strong>HackTricks in</strong> <a href="https://twitter.com/carlospolopm"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch</strong></a> <strong>Wed - 18.30(UTC) 🎙️</strong> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
|
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|
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* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
|
|
* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
|
|
* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
|
|
* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
|
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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