zebra: fix sockaddr_dl length assumptions (BZ#737)

Quagga makes bad assumptions about sockaddr_dl (on NetBSD, but possibly
on other systems as well).  Particularly, sizeof(struct sockaddr_dl)
returns a size that does not include the full sdl_data field, leading to
not enough data being copied.  This breaks IPv6 RAs in particular, as
a broken mac address from sockaddr_dl will be included in the packets.

From: Matthias-Christian Ott <ott@mirix.org>
Tested-by: Uwe Toenjes <6bone@6bone.informatik.uni-leipzig.de>
[further simplified + more comments]
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/if.h b/lib/if.h
index 841ce51e..2116e12e 100644
--- a/lib/if.h
+++ b/lib/if.h
@@ -103,7 +103,13 @@ struct interface
 
   /* Hardware address. */
 #ifdef HAVE_STRUCT_SOCKADDR_DL
-  struct sockaddr_dl sdl;
+  union {
+    /* note that sdl_storage is never accessed, it only exists to make space.
+     * all actual uses refer to sdl - but use sizeof(sdl_storage)!  this fits
+     * best with C aliasing rules. */
+    struct sockaddr_dl sdl;
+    struct sockaddr_storage sdl_storage;
+  };
 #else
   unsigned short hw_type;
   u_char hw_addr[INTERFACE_HWADDR_MAX];