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</details>
## Basic Information
An IPC (Inter-Process Communication) namespace is a Linux kernel feature that provides **isolation** of System V IPC objects, such as message queues, shared memory segments, and semaphores. This isolation ensures that processes in **different IPC namespaces cannot directly access or modify each other's IPC objects**, providing an additional layer of security and privacy between process groups.
### How it works:
1. When a new IPC namespace is created, it starts with a **completely isolated set of System V IPC objects**. This means that processes running in the new IPC namespace cannot access or interfere with the IPC objects in other namespaces or the host system by default.
2. IPC objects created within a namespace are visible and **accessible only to processes within that namespace**. Each IPC object is identified by a unique key within its namespace. Although the key may be identical in different namespaces, the objects themselves are isolated and cannot be accessed across namespaces.
3. Processes can move between namespaces using the `setns()` system call or create new namespaces using the `unshare()` or `clone()` system calls with the `CLONE_NEWIPC` flag. When a process moves to a new namespace or creates one, it will start using the IPC objects associated with that namespace.
## Lab:
### Create different Namespaces
#### CLI
```bash
sudo unshare -i [--mount-proc] /bin/bash
```
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**.
If you run the previous line without `-f` you will get that error.\
The error is caused by the PID 1 process exits in the new namespace.
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:
```
unshare -p /bin/bash
```
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.
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.
You can resolve this issue by use the '-f' option:
```
unshare -fp /bin/bash
```
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.
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)
</details>
#### Docker
```bash
docker run -ti --name ubuntu1 -v /usr:/ubuntu1 ubuntu bash
```
###  Check which namespace is your process in
sudo find /proc -maxdepth 3 -type l -name ipc -exec ls -l {} \; 2>/dev/null | grep <ns-number>
```
{% endcode %}
### Enter inside an IPC namespace
```bash
nsenter -i TARGET_PID --pid /bin/bash
```
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/net`).
* 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)!
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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).
