signal: Ensure no siginfo union member increases the size of struct siginfo

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/kernel/signal.c b/kernel/signal.c
index 241d549..b9e5d82 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3688,6 +3688,7 @@
 	/* If this check fails, the __ARCH_SI_PREAMBLE_SIZE value is wrong! */
 	BUILD_BUG_ON(__ARCH_SI_PREAMBLE_SIZE
 		!= offsetof(struct siginfo, _sifields._pad));
+	BUILD_BUG_ON(sizeof(struct siginfo) != SI_MAX_SIZE);
 
 	sigqueue_cachep = KMEM_CACHE(sigqueue, SLAB_PANIC);
 }