That's a good example. I guess there's other mitigation at work here. In my case if I'm in a public wifi area and connecting to my work PC then I'm using VPN to access smb. Smb just isn't open to the wifi attacker.

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.