tree ccc656d131b69a3d250bb79737aa64b52b289f19
parent 7a539a57d797a3db021e9d1f8cbaf6794aa7c2ea
author Hanno Becker <hanno.becker@arm.com> 1539783794 +0100
committer Hanno Becker <hanno.becker@arm.com> 1539784456 +0100

Fail when encountering invalid CBC padding in EtM records

This commit changes the behavior of the record decryption routine
`ssl_decrypt_buf()` in the following situation:
1. A CBC ciphersuite with Encrypt-then-MAC is used.
2. A record with valid MAC but invalid CBC padding is received.
In this situation, the previous code would not raise and error but
instead forward the decrypted packet, including the wrong padding,
to the user.

This commit changes this behavior to return the error
MBEDTLS_ERR_SSL_INVALID_MAC instead.

While erroneous, the previous behavior does not constitute a
security flaw since it can only happen for properly authenticated
records, that is, if the peer makes a mistake while preparing the
padded plaintext.