From 33129481cf61c4ce106d7dcb7d617b5ae9a4339a Mon Sep 17 00:00:00 2001
From: rnhmjoj <rnhmjoj@inventati.org>
Date: Tue, 22 Aug 2023 11:23:55 +0200
Subject: [PATCH] fix handling of IPv6 UDP connections

Problem:
IPv6 addresses are 4 bytes long and don't fit inside a `sockaddr`, so
`recvfrom` will truncate the address to the first half.
When generating a reply, the remaining half of the address is filled
with garbage and the packet is subsequently delivered to the wrong host,
if not immediately dropped.

Solution:
replace `sockaddr` with `sockaddr_storage`, the latter is guaranteed to
be large enough to hold an IPv6 address and pointers can be cast to
`sockaddr *` when needed.
---
 common.h       | 2 +-
 udp-listener.c | 8 ++++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/common.h b/common.h
index 6f6e76c..6a011f4 100644
--- a/common.h
+++ b/common.h
@@ -112,7 +112,7 @@ struct connection {
     struct queue q[2];
 
     /* SOCK_DGRAM */
-    struct sockaddr client_addr; /* Contains the remote client address */
+    struct sockaddr_storage client_addr; /* Contains the remote client address */
     socklen_t addrlen;
 
     int local_endpoint; /* Contains the local address */
diff --git a/udp-listener.c b/udp-listener.c
index 54881e2..0fb82ca 100644
--- a/udp-listener.c
+++ b/udp-listener.c
@@ -129,7 +129,7 @@ void udp_init(struct loop_info* fd_info)
  * If yes, returns file descriptor of connection
  * If not, returns -1
  * */
-static int known_source(hash* h, struct sockaddr* addr, socklen_t addrlen)
+static int known_source(hash* h, struct sockaddr_storage* addr, socklen_t addrlen)
 {
     struct connection search;
     search.client_addr = *addr;
@@ -243,7 +243,7 @@ static int nonblocking_socket(struct sslhcfg_protocols_item* proto)
 struct connection* udp_c2s_forward(int sockfd, struct loop_info* fd_info)
 {
     char addr_str[NI_MAXHOST+1+NI_MAXSERV+1];
-    struct sockaddr src_addr;
+    struct sockaddr_storage src_addr;
     struct addrinfo addrinfo;
     struct sslhcfg_protocols_item* proto;
     cnx_collection* collection = fd_info->collection;
@@ -259,13 +259,13 @@ struct connection* udp_c2s_forward(int sockfd, struct loop_info* fd_info)
     udp_timeouts(fd_info);
 
     addrlen = sizeof(src_addr);
-    len = recvfrom(sockfd, data, sizeof(data), 0, &src_addr, &addrlen);
+    len = recvfrom(sockfd, data, sizeof(data), 0, (struct sockaddr*) &src_addr, &addrlen);
     if (len < 0) {
         perror("recvfrom");
         return NULL;
     }
     target = known_source(fd_info->hash_sources, &src_addr, addrlen);
-    addrinfo.ai_addr = &src_addr;
+    addrinfo.ai_addr = (struct sockaddr*) &src_addr;
     addrinfo.ai_addrlen = addrlen;
     print_message(msg_probe_info, "received %ld UDP from %d:%s\n", 
                   len, target, sprintaddr(addr_str, sizeof(addr_str), &addrinfo));