Comment 0 for bug 1881982

Hi,

I have found a security issue on whoopsie 0.2.69 and earlier.

## Vulnerability in whoopsie
- whoopsie 0.2.69 and earlier have a memory leak vulnerability.
- An attacker can cause a denial of service (application crash) via a crafted .crash file.

## Basic
When a program has been crashed, Linux system tries to create a '.crash' file on '/var/crash/' directory with python script located in '/usr/share/apport/apport'.
The file contains a series of system crash information including core dump, syslog, stack trace, memory map info, etc.
A user is given read and write permission to the file.
After then, whoopsie parses key-value pairs in ‘.crash’ file and encodes it into binary json (bson) format.
Lastly, whoopsie forwards the data to a remotely connected Ubuntu error report system.

## Vulnerability
We have found a memory leak vulnerability during the parsing the crash file, when a collision occurs on GHashTable through g_hash_table_insert().
According to [1], if the key already exists in the GHashTable, its current value is replaced with the new value.
If 'key_destory_func' and 'value_destroy_func' are supplied when creating the table, the old value and the passed key are freed using that function.
Unfortunately, whoopsie does not handle the old value and the passed key when collision happens.
If a crash file contains same repetitive key-value pairs, it leads to memory leak as much as the amount of repetition and results in denial-of-service.

## Attack
1) Create a fake.crash file
memory_leak_poc.py script measures an available memory and generates a malicious crash file that contains same repetitive key-value pairs as much as 20% of the available memory size; 'ProblemType: Crash'.
The reason for 20% is that we just check the memory leakage.
2) Before the attack, it checks memory usage of whoopsie process with psutil
3) It triggers the whoopsie to read the fake.crash file
4) Then, it measures the memory usage of whoopsie process
5) It results in denial-of-service and then other users can no longer report crash to the Ubuntu error report system.

## Mitigation
We should use g_hash_table_new_full() with ‘key_destroy_func’ and ‘value_destroy_func’ functions instead of g_hash_table_new().
Otherwise, before g_hash_table_insert(), we should check the collision via g_hash_table_lookup_extended() and obtain pointer to the old value and remove it.

Sincerely,

[1] https://developer.gnome.org/glib/stable/glib-Hash-Tables.html#g-hash-table-insert