tree 4c388c5780ccfd5ec17a65f7910603b738287305
parent 172b291d3db3fa17b51e76cf02eb2d5e24db1af0
author David Benjamin <davidben@google.com> 1678942887 -0400
committer Boringssl LUCI CQ <boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com> 1679437119 +0000

Reimplement X509 parsing without templates

This is a cursory conversion and is, currently, very tedious because it
needs to bridge calling conventions. After tasn_*.c and all the
underlying primitives have CBS/CBB-based calling conventions, this
should be a lot cleaner.

This is to break a dependency cycle:

- We'd like to rewrite d2i_X509 with CBS

- To do that, we need to rewrite its underlying types with CBS

- Those parsers are tied up in tasn_dec.c, so we effectively need to
  rewrite tasn_dec.c with CBS.

- CBS is designed for DER, not BER, so such a change would most
  naturally switch the TLV parser to require DER.

- We've *almost* done that already except
  https://boringssl-review.googlesource.com/c/boringssl/+/51626 had to
  stop at non-minimal definite lengths, which are allowed in BER but
  forbidden in DER. See b/18228011 for a bunch of certificates which
  have a non-minimal definite length at *just* the signature field.

- So, to do that, we'd ideally special case just that field, or BIT
  STRINGs in general, to tolerate minimal lengths. That's easiest done
  when d2i_X509 is CBS, so we can just do what we want in imperative
  code. And thus we're back full circle.

So, detach X509 from the templates now. It's a bit tedious because we
need to switch calling conventions for now, but it breaks the cycle.
Later, we can revisit this and get all the benefits of a fully CBS-based
path.

For now, I haven't added an ASN1_ITEM. If it comes up, we can make an
EXTERN ASN1_ITEM.

Update-Note: The ASN1_ITEM removal means custom ASN.1 templates (which
are discouraged in favor of our much simpler CBS and CBB types) using
X509 will fail to compile. We don't believe anyone is relying on this,
but this can be restored if we find something.

Update-Note: Certificate parsing is slightly stricter: the outermost
TLVs, except for the signature field, no longer accept non-minimal
lengths, as mandated by DER. This strictness was broadly already applied
by the libssl parser.

Bug: 547
Change-Id: Ie5ad8ba4bb39f54fdd3dd45c53965b72a3850709
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/58185
Reviewed-by: Bob Beck <bbe@google.com>
Commit-Queue: David Benjamin <davidben@google.com>