Don't allow parts of a compound (SEQUENCE or SET) to go beyond the
containing compound.
The inline CSR regression test is derived from the existing "X509 CSR
ASN.1 (OK)" DER test vector. In the extensionRequest attribute, the original
well-formed fragment is:
a029 3027 06092a864886f70d01090e 311a 3018 ...
where 31 1a is the SET containing the Extensions sequence and 30 18 is the
contained Extensions sequence. The malformed test changes only the SET
length byte, from 1a to 19:
a029 3027 06092a864886f70d01090e 3119 3018 ...
The attribute SEQUENCE length and the inner Extensions sequence length are
left unchanged. This makes the SET one byte too short for its containing
attribute, so the parser must reject it with
MBEDTLS_ERR_ASN1_LENGTH_MISMATCH instead of parsing the trailing byte as
data outside the SET.
There is no known security impact, just some risk reduction.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
