[PATCH 6/6] alfred: validate the IPv4 multicast group argument

The return value of inet_pton() was ignored when parsing the -4
option. A mistyped group address left alfred_mcast untouched, so the
daemon continued with the first bytes of the IPv6 default group
(255.2.0.0) as IPv4 multicast group. Instead of a clear parse error
the user only got confusing 'can't add multicast membership' failures
at runtime.

Reject the option argument when it is not a valid IPv4 address.

Fixes: c7da798113a2 ("alfred: IPv4 multicast distribution support.")
Signed-off-by: Sven Eckelmann <[email protected]>
---
 main.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/main.c b/main.c
index 6372ec8..3953020 100644
--- a/main.c
+++ b/main.c
@@ -330,7 +330,11 @@ static struct globals *alfred_init(int argc, char *argv[])
 			break;
 		case '4':
 			globals->ipv4mode = true;
-			inet_pton(AF_INET, optarg, &alfred_mcast.ipv4);
+			ret = inet_pton(AF_INET, optarg, &alfred_mcast.ipv4);
+			if (ret != 1) {
+				fprintf(stderr, "bad IPv4 multicast group argument\n");
+				return NULL;
+			}
 			printf(" ** IPv4 Multicast Mode: %x\n", alfred_mcast.ipv4.s_addr);
 			break;
 		case 'f':

-- 
2.47.3