Crypt::OpenSSL::PKCS12 versions before 1.98 for Perl allow a NULL pointer dereference in print_attribute via a zero length BMPSTRING attribute

Crypt::OpenSSL::PKCS12 versions before 1.98 for Perl allow a NULL pointer dereference in print_attribute via a zero length BMPSTRING attribute. print_attribute() sizes the destination buffer for a BMPSTRING attribute from its declared byte length with `Renew(*attribute, length, char)`. A zero length attribute makes that a zero size reallocation, which Perl implements as a free returning NULL, so the buffer pointer becomes NULL, the following `strncpy` copies nothing, and the caller dereferences NULL in the `strlen()` it passes to `newSVpvn()`. A zero length BMPSTRING is even length, so the ASN.1 decoder accepts it and the value reaches this code. The UTF8STRING, OCTET STRING and BIT STRING arms size on `length + 1` or `length * 4 + 1` and are unaffected. Any caller that passes an untrusted PKCS#12 file to info_as_hash() can crash the process. info() prints attribute values directly without sizing a buffer and is unaffected.

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