Having to check for header_len == len and a last byte of 0x80 is
actually unambiguous, but not obvious. Before we supported multi-byte
tags, a two-byte header was always {tag, 0x80}, but now a three-byte
header could be {tag1, tag2, 0x80}. But a 0x80 suffix could also be
{tag, 0x81, 0x80} for a 128-byte definite-length element.
This is unambiguous because header_len == len implies either zero length
or indefinite-length, and it is not possible to encode a definite length
of zero, in BER or DER, with a header that ends in 0x80. Still, rather
than go through all this, we can just report indefinite lengths to the
caller directly.
Update-Note: This is a breaking change to CBS_get_any_ber_asn1_element.
There is only one external caller of this function, and it should be
possible to fix them atomically with this change, so I haven't bothered
introducing another name, etc. (See cl/429632075 for the fix.)
Change-Id: Ic94dab562724fd0b388bc8d2a7a223f21a8da413
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/51625
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
David Benjamin
7fac386a15