CGroup Namespace

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Basic Information

Cgroup namespace je funkcija Linux kernela koja pruža izolaciju cgroup hijerarhija za procese koji se izvršavaju unutar namespace-a. Cgroups, skraćeno za kontrolne grupe, su funkcija kernela koja omogućava organizovanje procesa u hijerarhijske grupe radi upravljanja i sprovođenja ograničenja na sistemske resurse kao što su CPU, memorija i I/O.

Iako cgroup namespace-i nisu poseban tip namespace-a kao što su drugi koje smo ranije diskutovali (PID, mount, network, itd.), oni su povezani sa konceptom izolacije namespace-a. Cgroup namespace-i virtualizuju pogled na cgroup hijerarhiju, tako da procesi koji se izvršavaju unutar cgroup namespace-a imaju drugačiji pogled na hijerarhiju u poređenju sa procesima koji se izvršavaju na hostu ili u drugim namespace-ima.

How it works:

1. Kada se kreira novi cgroup namespace, on počinje sa pogledom na cgroup hijerarhiju zasnovanom na cgroup-u procesa koji ga kreira. To znači da će procesi koji se izvršavaju u novom cgroup namespace-u videti samo podskup cele cgroup hijerarhije, ograničen na cgroup podstablo koje se oslanja na cgroup procesa koji ga kreira.

2. Procesi unutar cgroup namespace-a će videti svoju vlastitu cgroup kao koren hijerarhije. To znači da, iz perspektive procesa unutar namespace-a, njihova vlastita cgroup se pojavljuje kao koren, i ne mogu videti ili pristupiti cgroup-ima van svog podstabla.

3. Cgroup namespace-i ne pružaju direktno izolaciju resursa; oni samo pružaju izolaciju pogleda na cgroup hijerarhiju. Kontrola i izolacija resursa se i dalje sprovode od strane cgroup pod sistema (npr., cpu, memorija, itd.) sami.

Za više informacija o CGroups proverite:

CGroups

Lab:

Create different Namespaces

CLI

sudo unshare -C [--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 tačnu i izolovanu sliku informacija o procesima specifičnim za tu imensku oblast.

Greška: bash: fork: Ne može da dodeli memoriju

When unshare is executed without the -f option, an error is encountered due to the way Linux handles new PID (Process ID) namespaces. The key details and the solution are outlined below:

1. Objašnjenje problema:

• The Linux kernel allows a process to create new namespaces using the unshare system call. However, the process that initiates the creation of a new PID namespace (referred to as the "unshare" process) does not enter the new namespace; only its child processes do.

• Running %unshare -p /bin/bash% starts /bin/bash in the same process as unshare. Consequently, /bin/bash and its child processes are in the original PID namespace.

• The first child process of /bin/bash in the new namespace becomes PID 1. When this process exits, it triggers the cleanup of the namespace if there are no other processes, as PID 1 has the special role of adopting orphan processes. The Linux kernel will then disable PID allocation in that namespace.

2. Posledica:

• The exit of PID 1 in a new namespace leads to the cleaning of the PIDNS_HASH_ADDING flag. This results in the alloc_pid function failing to allocate a new PID when creating a new process, producing the "Cannot allocate memory" error.

3. Rešenje:

• The issue can be resolved by using the -f option with unshare. This option makes unshare fork a new process after creating the new PID namespace.

• Executing %unshare -fp /bin/bash% ensures that the unshare command itself becomes PID 1 in the new namespace. /bin/bash and its child processes are then safely contained within this new namespace, preventing the premature exit of PID 1 and allowing normal PID allocation.

By ensuring that unshare runs with the -f flag, the new PID namespace is correctly maintained, allowing /bin/bash and its sub-processes to operate without encountering the memory allocation error.

Docker

docker run -ti --name ubuntu1 -v /usr:/ubuntu1 ubuntu bash

Proverite u kojem je namespace vaš proces

ls -l /proc/self/ns/cgroup
lrwxrwxrwx 1 root root 0 Apr  4 21:19 /proc/self/ns/cgroup -> 'cgroup:[4026531835]'

Pronađite sve CGroup imenske prostore

sudo find /proc -maxdepth 3 -type l -name cgroup -exec readlink {} \; 2>/dev/null | sort -u
# Find the processes with an specific namespace
sudo find /proc -maxdepth 3 -type l -name cgroup -exec ls -l  {} \; 2>/dev/null | grep <ns-number>

Uđite unutar CGroup imenskog prostora

nsenter -C TARGET_PID --pid /bin/bash

Takođe, možete ući u drugi procesni prostor imena samo ako ste root. I ne možete ući u drugo ime prostora bez deskriptora koji na njega ukazuje (kao što je /proc/self/ns/cgroup).

Reference

• https://stackoverflow.com/questions/44666700/unshare-pid-bin-bash-fork-cannot-allocate-memory

Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE) Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

Support HackTricks

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• Join the 💬 Discord group or the telegram group or follow us on Twitter 🐦 @hacktricks_live.

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