[PATCH] Fix strict-aliasing warning in resolv/res_hconf.c

[Steve Ellcey]

On Wed, 2015-05-20 at 10:42 +0200, Florian Weimer wrote:
> On 05/20/2015 10:23 AM, Andreas Schwab wrote:
> > Florian Weimer <fweimer@redhat.com> writes:
> > 
> >> Looking at struct ifreq, it is rather mysterious to me how this is
> >> supposed to work at all.  I mean, struct sockaddr has just 14 bytes
> >> storage for address information, but IPv6 addresses need 16 bytes, and
> >> socket addresses contain even more information than a raw address.
> > 
> > This ioctl is only defined for IPv4.
> 
> Oh, but then we can add a union member of the appropriate type (just one
> is needed):
> 
> diff --git a/sysdeps/gnu/net/if.h b/sysdeps/gnu/net/if.h
> index 49a048c..39f40de 100644
> --- a/sysdeps/gnu/net/if.h
> +++ b/sysdeps/gnu/net/if.h
> @@ -24,6 +24,7 @@
>  #ifdef __USE_MISC
>  # include <sys/types.h>
>  # include <sys/socket.h>
> +# include <netinet/in.h>
>  #endif
> 
> 
> @@ -139,6 +140,7 @@ struct ifreq
>  	struct sockaddr ifru_broadaddr;
>  	struct sockaddr ifru_netmask;
>  	struct sockaddr ifru_hwaddr;
> +	struct sockaddr_in ifru_addr_in;
>  	short int ifru_flags;
>  	int ifru_ivalue;
>  	int ifru_mtu;
> 
> 
> This doesn't change ABI.  And then the code in resolv/res_hconf.c could
> use that new member, without any casts.

I don't know if this change is going to be considered acceptable or not
but here is a complete patch with the new union member, a macro
definition to access it (in order to match the other union members) and
the needed change to resolv/res_hconf.c.

Steve Ellcey
sellcey@imgtec.com


2015-05-20  Steve Ellcey  <sellcey@imgtec.com>
	    Florian Weimer  <fweimer@redhat.com>

	* resolv/res_hconf.c (_res_hconf_reorder_addrs): Use new ifr_addr_in
	name to access address.
	* sysdeps/gnu/net/if.h (struct ifreq): Add new ifru_addr_in union
	member.
	(ifr_addr_in): New macro.


diff --git a/resolv/res_hconf.c b/resolv/res_hconf.c
index 73942e8..3b05287 100644
--- a/resolv/res_hconf.c
+++ b/resolv/res_hconf.c
@@ -444,13 +444,13 @@ _res_hconf_reorder_addrs (struct hostent *hp)
 
 	      ifaddrs[new_num_ifs].addrtype = AF_INET;
 	      ifaddrs[new_num_ifs].u.ipv4.addr =
-		((struct sockaddr_in *) &cur_ifr->ifr_addr)->sin_addr.s_addr;
+		cur_ifr->ifr_addr_in.sin_addr.s_addr;
 
 	      if (__ioctl (sd, SIOCGIFNETMASK, cur_ifr) < 0)
 		continue;
 
 	      ifaddrs[new_num_ifs].u.ipv4.mask =
-		((struct sockaddr_in *) &cur_ifr->ifr_netmask)->sin_addr.s_addr;
+		cur_ifr->ifr_addr_in.sin_addr.s_addr;
 
 	      /* Now we're committed to this entry.  */
 	      ++new_num_ifs;
diff --git a/sysdeps/gnu/net/if.h b/sysdeps/gnu/net/if.h
index 49a048c..b741d14 100644
--- a/sysdeps/gnu/net/if.h
+++ b/sysdeps/gnu/net/if.h
@@ -24,6 +24,7 @@
 #ifdef __USE_MISC
 # include <sys/types.h>
 # include <sys/socket.h>
+# include <netinet/in.h>
 #endif
 
 
@@ -139,6 +140,7 @@ struct ifreq
 	struct sockaddr ifru_broadaddr;
 	struct sockaddr ifru_netmask;
 	struct sockaddr ifru_hwaddr;
+	struct sockaddr_in ifru_addr_in;
 	short int ifru_flags;
 	int ifru_ivalue;
 	int ifru_mtu;
@@ -151,6 +153,7 @@ struct ifreq
 # define ifr_name	ifr_ifrn.ifrn_name	/* interface name 	*/
 # define ifr_hwaddr	ifr_ifru.ifru_hwaddr	/* MAC address 		*/
 # define ifr_addr	ifr_ifru.ifru_addr	/* address		*/
+# define ifr_addr_in	ifr_ifru.ifru_addr_in	/* sockaddr_in address	*/
 # define ifr_dstaddr	ifr_ifru.ifru_dstaddr	/* other end of p-p lnk	*/
 # define ifr_broadaddr	ifr_ifru.ifru_broadaddr	/* broadcast address	*/
 # define ifr_netmask	ifr_ifru.ifru_netmask	/* interface net mask	*/