Make ASN1_NULL an opaque pointer.
crypto/asn1 represents an ASN.1 NULL value as a non-null ASN1_NULL*
pointer, (ASN1_NULL*)1. It is a non-null pointer because a null pointer
represents an omitted OPTIONAL NULL. It is an opaque pointer because
there is no sense in allocating anything.
This pointer cannot be dereferenced, yet ASN1_NULL is a typedef for int.
This is confusing and probably undefined behavior. (N1548, 6.3.2.3,
clause 7 requires pointer conversions between two pointer types be
correctly aligned, even if the pointer is never dereferenced. Strangely,
clause 5 above does not impose the same requirement when converting from
integer to pointer, though it mostly punts to the implementation
definition.) Of course, all of tasn_*.c is a giant strict aliasing
violation anyway, but an opaque struct pointer is a slightly better
choice here.
(Note that, although ASN1_BOOLEAN is also a typedef for int, that
situation is different: the ASN1_BOOLEAN representation is a plain
ASN1_BOOLEAN, not ASN1_BOOLEAN*, while the ASN1_NULL representation is a
pointer. ASN1_NULL could have had the same treatment and even used a
little less memory, but changing that would break the API.)
Update-Note: Code that was assuming ASN1_NULL was an int typedef will
fail to compile. Given this was never dereferencable, it is hard to
imagine anything relying on this.
Bug: 438
Change-Id: Ia0c652eed66e76f82a3843af1fc877f06c8d5e8f
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/49805
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/base.h b/include/openssl/base.h
index 8be10d1..01a7e07 100644
--- a/include/openssl/base.h
+++ b/include/openssl/base.h
@@ -328,8 +328,11 @@
// CRYPTO_THREADID is a dummy value.
typedef int CRYPTO_THREADID;
+// An |ASN1_NULL| is an opaque type. asn1.h represents the ASN.1 NULL value as
+// an opaque, non-NULL |ASN1_NULL*| pointer.
+typedef struct asn1_null_st ASN1_NULL;
+
typedef int ASN1_BOOLEAN;
-typedef int ASN1_NULL;
typedef struct ASN1_ITEM_st ASN1_ITEM;
typedef struct asn1_object_st ASN1_OBJECT;
typedef struct asn1_pctx_st ASN1_PCTX;
