transparent: workaround old glibc bug on RHEL7

it's been reported[0] that RHEL7 fails to properly set the length
parameter of the getsockname() call to the length of the required
struct sockaddr type, and always returns the length passed if it
is big enough.

the SOCKADDR_UNION_* macros originate from my microsocks[1] project,
and facilitate handling of the sockaddr mess without nasty casts.

[0]: https://github.com/tinyproxy/tinyproxy/issues/45#issuecomment-694594990
[1]: https://github.com/rofl0r/microsocks

2 files changed, 17 insertions, 5 deletions

diff --git a/src/sock.h b/src/sock.h
index 722371d..aee5bf5 100644
--- a/src/sock.h
+++ b/src/sock.h
@@ -31,6 +31,20 @@
 #include "common.h"
 #include "sblist.h"
 
+#define SOCKADDR_UNION_AF(PTR) (PTR)->v4.sin_family
+
+#define SOCKADDR_UNION_LENGTH(PTR) ( \
+	( SOCKADDR_UNION_AF(PTR) == AF_INET  ) ? sizeof((PTR)->v4) : ( \
+	( SOCKADDR_UNION_AF(PTR) == AF_INET6 ) ? sizeof((PTR)->v6) : 0 ) )
+
+#define SOCKADDR_UNION_ADDRESS(PTR) ( \
+	( SOCKADDR_UNION_AF(PTR) == AF_INET  ) ? (void*) &(PTR)->v4.sin_addr  : ( \
+	( SOCKADDR_UNION_AF(PTR) == AF_INET6 ) ? (void*) &(PTR)->v6.sin6_addr : (void*) 0 ) )
+
+#define SOCKADDR_UNION_PORT(PTR) ( \
+	( SOCKADDR_UNION_AF(PTR) == AF_INET  ) ? (PTR)->v4.sin_port  : ( \
+	( SOCKADDR_UNION_AF(PTR) == AF_INET6 ) ? (PTR)->v6.sin6_port : 0 ) )
+
 union sockaddr_union {
         struct sockaddr_in  v4;
         struct sockaddr_in6 v6;
diff --git a/src/transparent-proxy.c b/src/transparent-proxy.c
index e3265f9..d090ae3 100644
--- a/src/transparent-proxy.c
+++ b/src/transparent-proxy.c
@@ -83,16 +83,14 @@ do_transparent_proxy (struct conn_s *connptr, orderedmap hashofheaders,
                         return 0;
                 }
 
-                af = length == sizeof(dest_addr.v4) ? AF_INET : AF_INET6;
-                if (af == AF_INET) dest_inaddr = &dest_addr.v4.sin_addr;
-                else dest_inaddr = &dest_addr.v6.sin6_addr;
+                af = SOCKADDR_UNION_AF(&dest_addr);
+                dest_inaddr = SOCKADDR_UNION_ADDRESS(&dest_addr);
 
                 if (!inet_ntop(af, dest_inaddr, namebuf, sizeof namebuf))
                         goto addr_err;
 
                 request->host = safestrdup (namebuf);
-                request->port = ntohs (af == AF_INET ? dest_addr.v4.sin_port
-                                       : dest_addr.v6.sin6_port);
+                request->port = ntohs (SOCKADDR_UNION_PORT(&dest_addr));
 
                 request->path = (char *) safemalloc (ulen + 1);
                 strlcpy (request->path, *url, ulen + 1);