commit 0e73b48f77589f69a5418c211b77b95ed26520c8
author Michael Brown <mcb30@ipxe.org> Wed Aug 07 13:36:35 2024 +0100
committer Michael Brown <mcb30@ipxe.org> Wed Aug 07 16:11:57 2024 +0100
tree de940ab056a6affda4c7b75f64ddd2b715cfe11e
parent 309ac8fd21be744486ee8be2b64a446cbc754c99

[crypto] Clarify ASN.1 cursor invalidation behaviour

Calling asn1_skip_if_exists() on a malformed ASN.1 object may
currently leave the cursor in a partially-updated state, where the tag
byte and one of the length bytes have been stripped.  The cursor is
left with a valid data pointer and length and so no out-of-bounds
access can arise, but the cursor no longer points to the start of an
ASN.1 object.

Ensure that each ASN.1 cursor manipulation code path leads to the
cursor being either fully updated, left unmodified, or invalidated,
and update the function descriptions to reflect this.

Signed-off-by: Michael Brown <mcb30@ipxe.org>