CVE-2021-47176

What it actually does

Missing verify_path discipline function for FBA and DIAG DASD devices causes illegal operation exception when dasd_device_tasklet invokes path verification, leading to kernel panic.

Why it matters to the business

Unexpected crashes on s390 mainframes using FBA or DIAG storage devices can interrupt critical workloads and require manual recovery or reboots.

How an attack unfolds

Kernel operations or local events trigger path verification on an FBA or DIAG device; the renamed function pointer is absent so execution falls through to an invalid address and panics the system.

How to fix it

Apply a Linux kernel containing the wrapper that maps dasd_generic_verify_path for FBA and DIAG disciplines; rebuild and reboot affected s390 systems.

How to confirm the fix worked

Confirm the wrapper function definition exists in the dasd driver source; reproduce path events on FBA/DIAG devices and verify absence of panics in dmesg.

Typical attack path

1. Initiate DASD path event or verification request on FBA/DIAG device
2. dasd_device_tasklet executes the discipline function pointer
3. Missing function causes illegal operation exception and panic

How to detect it

Search kernel logs and crash dumps for illegal operation exceptions originating from dasd_device_tasklet on FBA or DIAG devices.

What your security team should do

• Patch to a fixed kernel release on all s390 systems using DASD
• Monitor kernel logs for dasd_device_tasklet illegal operation exceptions
• Test storage path failover on non-ECKD devices after patching