Comment 0 for bug 1939733

Application doesnt check the input values for extra_dhcp_opts port parameter allowing user to use a newline character. The values from extra_dhcp_opts are used in rendering of opts file which is passed to dnsmasq as a dhcp-optsfile. Considering this, an attacker can inject any options to that file.

The main direct impact in my opinion is that attacker can push arbitrary dhcp options to another instances connected to the same network. And due to we are able to modify our own port connected to external network, it is possible to push dhcp options to the instances of another tennants using the same external network.

If we go further, there is an known buffer overflow vulnerability in dnsmasq (https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commitdiff;h=7d04e17444793a840f98a0283968b96502b112dc) which was not considered as a security issue due to attacker cannot control dhcp opts in most cases and therefore this vulnerability is still exists in most distributives (e.g Ubuntu 20.04.1). In our case dhcp opts is exactly what attacker can modify, so we can trigger buffer overflow there. I even managed to write an exploit which lead to a remote code execution using this buffer overflow vulnerability.

Here the payload to crash dnsmasq as a proof of concept:
```
PUT /v2.0/ports/9db67e0f-537c-494a-a655-c8a0c518d57e HTTP/1.1
Host: openstack
X-Auth-Token: TOKEN
Content-Type: application/json
Content-Length: 170

{"port":{
"extra_dhcp_opts":[{"opt_name":"zzz",
"opt_value":"xxx\n128,aa:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\n120,aa.cc\n128,:"
}]}}
```

Tested on ocata, train and victoria versions.

Vulnerability was found by Pavel Toporkov