readme: add examples for memparse usage

This commit adds a new section to the README.md file that provides
an example of how to use the memparse sub-command.

Signed-off-by: Kouame Behouba Manasse <behouba@gmail.com>

README.md

@@ -15,6 +15,8 @@ Details on how to create checkpoints with the help of [CRIU][criu] can be found
 
 ## Usage
 
+### `show` sub-command
+
 To display an overview of a checkpoint archive you can just use
 `checkpointctl show`:
 
@@ -41,6 +43,8 @@ $ checkpointctl show /var/lib/kubelet/checkpoints/checkpoint-counters_default-co
 +-----------+------------------------------------+--------------+---------+--------------------------------+--------+------------+------------+
 ```
 
+### `inspect` sub-command
+
 To retrieve low-level information about a container checkpoint, use the `checkpointctl inspect` command:
 
 ```console
@@ -64,6 +68,91 @@ awesome_booth
 
 For a complete list of flags supported, use `checkpointctl inspect --help`.
 
+### `memparse` sub-command
+
+To perform memory analysis of container checkpoints, you can use the `checkpointctl memparse` command.
+
+```console
+$ checkpointctl memparse /path/to/checkpoints/jira.tar.gz  --pid=1 | less
+
+Displaying memory pages content for Process ID 1 from checkpoint: /home/behouba/checkpoints/jira.tar.gz
+
+Address           Hexadecimal                                       ASCII            
+-------------------------------------------------------------------------------------
+00005633bb080000  f3 0f 1e fa 48 83 ec 08 48 8b 05 d1 4f 00 00 48  |....H...H...O..H|
+00005633bb080010  85 c0 74 02 ff d0 48 83 c4 08 c3 00 00 00 00 00  |..t...H.........|
+00005633bb080020  ff 35 b2 4e 00 00 f2 ff 25 b3 4e 00 00 0f 1f 00  |.5.N....%.N.....|
+00005633bb080030  f3 0f 1e fa 68 00 00 00 00 f2 e9 e1 ff ff ff 90  |....h...........|
+*
+00005633bb0800a0  f3 0f 1e fa 68 07 00 00 00 f2 e9 71 ff ff ff 90  |....h......q....|
+00005633bb0800b0  f3 0f 1e fa 68 08 00 00 00 f2 e9 61 ff ff ff 90  |....h......a....|
+00005633bb0800c0  f3 0f 1e fa 68 09 00 00 00 f2 e9 51 ff ff ff 90  |....h......Q....|
+00005633bb0800d0  f3 0f 1e fa 68 0a 00 00 00 f2 e9 41 ff ff ff 90  |....h......A....|
+00005633bb0800e0  f3 0f 1e fa 68 0b 00 00 00 f2 e9 31 ff ff ff 90  |....h......1....|
+```
+
+Here's an example of memory analysis of a PostgreSQL container. In this case, we start a PostgreSQL container with a password set to 'mysecret'. Then, we create a checkpoint of the container and use the `memparse` to find the stored password.
+
+```console
+$ sudo podman run --name postgres -e POSTGRES_PASSWORD=mysecret -d postgres
+$ sudo podman container checkpoint -l --export=/tmp/postgres.tar.gz
+$ sudo checkpointctl memparse --pid 1 /tmp/postgres.tar.gz | grep -B 1 -A 1 mysecret
+000055dd725c1e60  50 4f 53 54 47 52 45 53 5f 50 41 53 53 57 4f 52  |POSTGRES_PASSWOR|
+000055dd725c1e70  44 3d 6d 79 73 65 63 72 65 74 00 00 00 00 00 00  |D=mysecret......|
+000055dd725c1e80  00 00 00 00 00 00 00 00 31 00 00 00 00 00 00 00  |........1.......|
+```
+
+Here's another scenario, of memory analysis for a web application container. We start a vulnerable web application container, perform an arbitrary code execution attack, create a checkpoint for forensic analysis while leaving the container running, and finally analyze the checkpoint memory to identify the injected code.
+
+```console
+# Start vulnerable web application
+$ sudo podman run --name dsvw -p 1234:8000 -d quay.io/rst0git/dsvw
+
+# Perform arbitrary code execution attack: $(echo secret)
+$ curl "http://localhost:1234/?domain=www.google.com%3B%20echo%20secret"
+nslookup: can't resolve '(null)': Name does not resolve
+
+Name:      www.google.com
+Address 1: 142.250.187.228 lhr25s34-in-f4.1e100.net
+Address 2: 2a00:1450:4009:820::2004 lhr25s34-in-x04.1e100.net
+secret
+(reverse-i-search)`': ^C
+
+# Create a checkpoint for forensic analysis and leave the container running
+$ sudo podman container checkpoint --leave-running -l -e /tmp/dsvw.tar
+
+# Analyse checkpoint memory to identify the attacker's injected code
+$ sudo checkpointctl memparse --pid 1 /tmp/dsvw.tar | grep 'echo secret'
+00007faac5711f60  6f 6d 3b 20 65 63 68 6f 20 73 65 63 72 65 74 00  |om; echo secret.|
+```
+
+For larger processes, it's recommended to write the contents of process memory pages to a file rather than standard output.
+
+To get an overview of process memory sizes within the checkpoint, run `checkpointctl memparse` without arguments.
+
+```console
+$ sudo ./checkpointctl memparse /tmp/jira.tar.gz 
+
+Displaying processes memory sizes from /tmp/jira.tar.gz
+
++-----+--------------+-------------+
+| PID | PROCESS NAME | MEMORY SIZE |
++-----+--------------+-------------+
+|   1 | tini         | 100.0 KiB   |
++-----+--------------+-------------+
+|   2 | java         | 553.5 MiB   |
++-----+--------------+-------------+
+```
+
+In this case given the large size of the java process, it is better to write it output to a file.
+
+```console
+$ sudo ./checkpointctl memparse --pid=2 /tmp/jira.tar.gz --output=/tmp/java-memory-pages.txt
+Writing memory pages content for process ID 2 from checkpoint: /tmp/jira.tar.gz to file: /tmp/java-memory-pages.txt...
+```
+
+Please note that writing large memory pages to a file can take several minutes.
+
 ## Installing from source code
 
 1. Clone the repository.