[PATCH net-next v2] tunnels: correct conditional build of MPLS and IPv6

[Simon Horman]

Using a combination if #if conditionals and goto labels to unwind
tunnel4_init seems unwieldy. This patch takes a simpler approach of
directly unregistering previously registered protocols when an error
occurs.

This fixes a number of problems with the current implementation
including the potential presence of labels when they are unused
and the potential absence of unregister code when it is needed.

Fixes: 8afe97e5d416 ("tunnels: support MPLS over IPv4 tunnels")
Signed-off-by: Simon Horman <simon.hor...@netronome.com>
---
 net/ipv4/tunnel4.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/net/ipv4/tunnel4.c b/net/ipv4/tunnel4.c
index 45cd4253583a..ec35eaa5c029 100644
--- a/net/ipv4/tunnel4.c
+++ b/net/ipv4/tunnel4.c
@@ -208,24 +208,25 @@ static const struct net_protocol tunnelmpls4_protocol = {
 static int __init tunnel4_init(void)
 {
        if (inet_add_protocol(&tunnel4_protocol, IPPROTO_IPIP))
-               goto err_ipip;
+               goto err;
 #if IS_ENABLED(CONFIG_IPV6)
-       if (inet_add_protocol(&tunnel64_protocol, IPPROTO_IPV6))
-               goto err_ipv6;
+       if (inet_add_protocol(&tunnel64_protocol, IPPROTO_IPV6)) {
+               inet_del_protocol(&tunnel4_protocol, IPPROTO_IPIP);
+               goto err;
+       }
 #endif
 #if IS_ENABLED(CONFIG_MPLS)
-       if (inet_add_protocol(&tunnelmpls4_protocol, IPPROTO_MPLS))
-               goto err_mpls;
+       if (inet_add_protocol(&tunnelmpls4_protocol, IPPROTO_MPLS)) {
+               inet_del_protocol(&tunnel4_protocol, IPPROTO_IPIP);
+#if IS_ENABLED(CONFIG_IPV6)
+               inet_del_protocol(&tunnel64_protocol, IPPROTO_IPV6);
+#endif
+               goto err;
+       }
 #endif
        return 0;
 
-#if IS_ENABLED(CONFIG_IPV6)
-err_mpls:
-       inet_del_protocol(&tunnel4_protocol, IPPROTO_IPV6);
-#endif
-err_ipv6:
-       inet_del_protocol(&tunnel4_protocol, IPPROTO_IPIP);
-err_ipip:
+err:
        pr_err("%s: can't add protocol\n", __func__);
        return -EAGAIN;
 }
-- 
2.7.0.rc3.207.g0ac5344