In a TLS client, when using certificate authentication, the client should
check that the certificate is valid for the server name that the client
expects. Otherwise, in most scenarios, a malicious server can impersonate
another server.
Normally, the application code should call mbedtls_ssl_set_hostname().
However, it's easy to forget. So raise an error if mandatory certificate
authentication is in effect and mbedtls_ssl_set_hostname() has not been
called. Raise the new error code
MBEDTLS_ERR_SSL_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME, for easy
identification.
But don't raise the error if the backward compatibility option
MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME is
enabled.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
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