CVE-2021-47178 — scsi: target: core: Avoid smp_processor_id() in preemptible code

Affected: Linux

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 smp_processor_id(), get CPU ID with raw_smp_processor_id() instead. The CPU ID is used for performance improvement then thread move to other CPU will not affect the code.

[1]

[ 56.468103] run blktests block/005 at 2021-05-12 14:16:38 [ 57.369473] check_preemption_disabled: 85 callbacks suppressed [ 57.369480] BUG: using smp_processor_id() in preemptible [00000000] code: fio/1511 [ 57.369506] BUG: using smp_processor_id() in preemptible [00000000] code: fio/1510 [ 57.369512] BUG: using…

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CVE-2021-47178 — scsi: target: core: Avoid smp_processor_id() in preemptible code