CVE-2026-31638: NULL Pointer Dereference

In the Linux kernel, the following vulnerability has been resolved:

rxrpc: Only put the call ref if one was acquired

rxrpc_input_packet_on_conn() can process a to-client packet after the current client call on the channel has already been torn down. In that case chan->call is NULL, rxrpc_try_get_call() returns NULL and there is no reference to drop.

The client-side implicit-end error path does not account for that and unconditionally calls rxrpc_put_call(). This turns a protocol error path into a kernel crash instead of rejecting the packet.

Only drop the call reference if one was actually acquired. Keep the existing protocol error handling unchanged.