Linux kernel (net/tls): A zero-length record already sitting on the rx_list breaks the invariant that zero-copy decrypt

Impact

A zero-length record already sitting on the rx_list breaks the invariant that zero-copy decrypt never has to queue an skb. The receive path then tries to queue a record it decrypted straight into the user buffer and has no skb to work with, corrupting the receive state of a connection a remote peer controls.

Who can reach it

Remote: the peer sends a zero-length TLS record and then a record of a different type, which is entirely within its control on any kTLS connection. Applies to any tenant-facing or fabric-facing kTLS RX socket on the node; no local privilege required.

What to do

Boot a kernel carrying the linked stable commits. Interim: terminate TLS in userspace for connections to untrusted peers.

References