CVE-2021-47178

/// Technical description

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

scsi: target: core: Avoid smp_processor_id() in preemptible code

The BUG message "BUG: using smp_processor_id() in preemptible [00000000]

code" was observed for TCMU devices with kernel config DEBUG_PREEMPT.

The message was observed when blktests block/005 was run on TCMU devices

with fileio backend or user:zbc backend [1]. The commit 1130b499b4a7

("scsi: target: tcm_loop: Use LIO wq cmd submission helper") triggered the

symptom. The commit modified work queue to handle commands and changed

'current->nr_cpu_allowed' at smp_processor_id() call.

The message was also observed at system shutdown when TCMU devices were not

cleaned up [2]. The function smp_processor_id() was called in SCSI host

work queue for abort handling, and triggered the BUG message. This symptom

was observed regardless of the commit 1130b499b4a7 ("scsi: target:

tcm_loop: Use LIO wq cmd submission helper").

To avoid the preemptible code check at sm

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References