The thing is, not every protocol offers TLS. Take SMB (network shares) for example... encryption is only offered as of v3 and if a company/university wants to allow Windows 7 clients, they're capped to SMB v2.1.
In a case that it is, its curious how you would inject data into a smb stream and not fail checksums from client-side chechking. Maybe its trivial to deal with this, not sure.
If the WPA2 protected wifi network is using AES, which is the most common in my experience, then they won't be able to inject any data. From the Krack website:
If the victim uses either the WPA-TKIP or GCMP encryption protocol, instead of AES-CCMP, the impact is especially catastrophic. Against these encryption protocols, nonce reuse enables an adversary to not only decrypt, but also to forge and inject packets.