[Openvpn-devel] [XS] Change in openvpn[master]: Prevent crash on invalid server-ipv6 argument

[klemens (C. Review) <ge...@op...>]

Attention is currently required from: plaisthos.

Hello plaisthos,

I'd like you to do a code review.
Please visit

    http://gerrit.openvpn.net/c/openvpn/+/1418?usp=email

to review the following change.


Change subject: Prevent crash on invalid server-ipv6 argument
......................................................................

Prevent crash on invalid server-ipv6 argument

`get_addr_generic()` expects `openvpn_getaddrinfo()` to return a newly
allocated struct, but getaddrinfo(3) failure leaves `*ai = NULL` as-is.

Unlike free(3), freegetaddrinfo(3) requires a valid struct, thus the
following is enough to trigger a NULL pointer dereference in libc:

```
$ openvpn --server-ipv6 ''
2025-12-06 11:59:18 RESOLVE: Cannot resolve host address: :[AF_INET6] (no address associated with name)
Segmentation fault (core dumped)
```

Guard against empty `ai`, i.e. failure, like similar code already does:

```
$ ./openvpn --server-ipv6 ''
2025-12-06 12:05:11 RESOLVE: Cannot resolve host address: :[AF_INET6] (no address associated with name)
Options error: error parsing --server-ipv6 parameter
Use --help for more information.
```

Spotted through a configuration typo "server-ipv6 fd00:/64" with 2.6.17,
reproduced with and tested against 2.7rc3 on OpenBSD/amd64 7.8-current.

Change-Id: I99a6604fdfc682f9609bfe7672aa78285084dcb9
Signed-off-by: Klemens Nanni <kn...@op...>
---
M src/openvpn/socket.c
1 file changed, 4 insertions(+), 1 deletion(-)



  git pull ssh://gerrit.openvpn.net:29418/openvpn refs/changes/18/1418/1

diff --git a/src/openvpn/socket.c b/src/openvpn/socket.c
index 46bedf4..80c2895 100644
--- a/src/openvpn/socket.c
+++ b/src/openvpn/socket.c
@@ -189,7 +189,10 @@
         *sep = '/';
     }
 out:
-    freeaddrinfo(ai);
+    if (ai)
+    {
+        freeaddrinfo(ai);
+    }
     free(var_host);
 
     return ret;

-- 
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Gerrit-MessageType: newchange
Gerrit-Project: openvpn
Gerrit-Branch: master
Gerrit-Change-Id: I99a6604fdfc682f9609bfe7672aa78285084dcb9
Gerrit-Change-Number: 1418
Gerrit-PatchSet: 1
Gerrit-Owner: klemens <kn...@op...>
Gerrit-Reviewer: plaisthos <arn...@rf...>
Gerrit-CC: openvpn-devel <ope...@li...>
Gerrit-Attention: plaisthos <arn...@rf...>