CVE-2024-46704

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

workqueue: Fix spruious data race in __flush_work()

When flushing a work item for cancellation, __flush_work() knows that it exclusively owns the work item through its PENDING bit. 134874e2eee9 ("workqueue: Allow cancel_work_sync() and disable_work() from atomic contexts on BH work items") added a read of @work->data to determine whether to use busy wait for BH work items that are being canceled. While the read is safe when @from_cancel, @work->data was read before testing @from_cancel to simplify code structure:

data = *work_data_bits(work);
if (from_cancel &&
    !WARN_ON_ONCE(data & WORK_STRUCT_PWQ) && (data & WORK_OFFQ_BH)) {

While the read data was never used if !@from_cancel, this could trigger KCSAN data race detection spuriously:

================================================================== BUG: KCSAN: data-race in __flush_work / __flush_work

write to 0xffff8881223aa3e8 of 8 bytes by task 3998 on cpu 0: instrument_write include/linux/instrumented.h:41 [inline] ___set_bit include/asm-generic/bitops/instrumented-non-atomic.h:28 [inline] insert_wq_barrier kernel/workqueue.c:3790 [inline] start_flush_work kernel/workqueue.c:4142 [inline] __flush_work+0x30b/0x570 kernel/workqueue.c:4178 flush_work kernel/workqueue.c:4229 [inline] ...

read to 0xffff8881223aa3e8 of 8 bytes by task 50 on cpu 1: __flush_work+0x42a/0x570 kernel/workqueue.c:4188 flush_work kernel/workqueue.c:4229 [inline] flush_delayed_work+0x66/0x70 kernel/workqueue.c:4251 ...

value changed: 0x0000000000400000 -> 0xffff88810006c00d

Reorganize the code so that @from_cancel is tested before @work->data is accessed. The only problem is triggering KCSAN detection spuriously. This shouldn't need READ_ONCE() or other access qualifiers.

No functional changes.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.