stun: Fix cast-align compiler warning when casting sockaddr

There should never be a problem with alignment at runtime, since we’re
casting the sockaddr to sockaddr_in or sockaddr_in6 based on its
declared sa_family — anything declared as AF_INET6 should have been
allocated as a sockaddr_in6, and hence have appropriate alignment (same
for AF_INET).

This fixes a compiler warning on ARM and other alignment-sensitive
architectures.

https://phabricator.freedesktop.org/T7718

Signed-off-by: Philip Withnall <withnall@endlessm.com>
Reviewed-by: Olivier Crête <olivier.crete@collabora.com>
Differential Revision: https://phabricator.freedesktop.org/D1686

1 files changed, 10 insertions, 2 deletions

diff --git a/stun/stunmessage.c b/stun/stunmessage.c
index 558fe5e..e8184c4 100644
--- a/stun/stunmessage.c
+++ b/stun/stunmessage.c
@@ -427,14 +427,22 @@ stun_message_append_addr (StunMessage *msg, StunAttribute type,
   uint16_t alen, port;
   uint8_t family;
 
+  union {
+    const struct sockaddr *addr;
+    const struct sockaddr_in *in;
+    const struct sockaddr_in6 *in6;
+  } sa;
+
   if ((size_t) addrlen < sizeof (struct sockaddr))
     return STUN_MESSAGE_RETURN_INVALID;
 
+  sa.addr = addr;
+
   switch (addr->sa_family)
   {
     case AF_INET:
       {
-        const struct sockaddr_in *ip4 = (const struct sockaddr_in *)addr;
+        const struct sockaddr_in *ip4 = sa.in;
         family = 1;
         port = ip4->sin_port;
         alen = 4;
@@ -444,7 +452,7 @@ stun_message_append_addr (StunMessage *msg, StunAttribute type,
 
     case AF_INET6:
       {
-        const struct sockaddr_in6 *ip6 = (const struct sockaddr_in6 *)addr;
+        const struct sockaddr_in6 *ip6 = sa.in6;
         if ((size_t) addrlen < sizeof (*ip6))
           return STUN_MESSAGE_RETURN_INVALID;