[PATCH xserver 1/2] os: Fix a type error in the IPv6 XDMCP code

[Adam Jackson]

Building with strict-aliasing rightly chirps here:

../os/xdmcp.c: In function ‘XdmcpRegisterConnection’:
../os/xdmcp.c:489:31: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
                     &((struct sockaddr_in6 *) &address)->sin6_addr.s6_addr[12];
                               ^~~~~~~~~~~~

We have "const char *address", so &address here is a char ** (i.e., it
points to the slot on the stack containing the pointer to the character
array passed in as an argument). Casting that to a struct sockaddr_in6 *
is wrong, because it means that area of the stack will be reinterpreted
as a struct sockaddr_in6.

Instead, cast address, not &address.

Signed-off-by: Adam Jackson <ajax at redhat.com>
---
 os/xdmcp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/os/xdmcp.c b/os/xdmcp.c
index 7aeb393e63..d8c81fbf83 100644
--- a/os/xdmcp.c
+++ b/os/xdmcp.c
@@ -486,7 +486,7 @@ XdmcpRegisterConnection(int type, const char *address, int addrlen)
                      IN6_IS_ADDR_V4MAPPED((const struct in6_addr *) address)) {
                 fromAddr = &((struct sockaddr_in *) &FromAddress)->sin_addr;
                 regAddr =
-                    &((struct sockaddr_in6 *) &address)->sin6_addr.s6_addr[12];
+                    &((struct sockaddr_in6 *) address)->sin6_addr.s6_addr[12];
                 regAddrlen = sizeof(struct in_addr);
             }
         }
-- 
2.14.3