psk_client_callback, 128-byte id bug.
Fix a bug in handling of 128 byte long PSK identity in psk_client_callback. OpenSSL supports PSK identities of up to (and including) 128 bytes in length. PSK identity is obtained via the psk_client_callback, implementors of which are expected to provide a NULL-terminated identity. However, the callback is invoked with only 128 bytes of storage thus making it impossible to return a 128 byte long identity and the required additional NULL byte. This CL fixes the issue by passing in a 129 byte long buffer into the psk_client_callback. As a safety precaution, this CL also zeroes out the buffer before passing it into the callback, uses strnlen for obtaining the length of the identity returned by the callback, and aborts the handshake if the identity (without the NULL terminator) is longer than 128 bytes. (Original patch amended to achieve strnlen in a different way.) Reviewed-by: Rich Salz <rsalz@openssl.org> (cherry picked from commit be0d8517)
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