tree f26e7b6dcb8a79171aaa524dd6bfbb3e16434c2a
parent f5e601275c38b0b2be437e392f654601725f9d66
author David Benjamin <davidben@google.com> 1633389661 -0400
committer Adam Langley <agl@google.com> 1633456896 +0000

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>