Linux Kernel CVE-2026-89558

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

md/raid10: fix still_degraded being inverted in raid10_sync_request()

Commit fe6a19d40ceb ("md/md-bitmap: merge md_bitmap_start_sync() into bitmap_operations") converted still_degraded from int to bool, but inverted the assignment in the loop that checks whether the array will still be degraded after the current device is recovered: "still_degraded = 1" became "still_degraded = false".

As a result, recovering a device while another mirror is still missing calls md_bitmap_start_sync() with degraded == false, which clears bitmap bits that the still-missing device needs. When that device is re-added, its bitmap-based recovery finds the bits already cleared and skips every region written while the array was degraded, so it is marked In_sync while holding stale data: silent corruption.

Reproducer (raid10 near=2, 4 disks, internal bitmap):

• fail and remove one disk of each mirror pair
• write to the degraded array
• re-add both disks and let recovery finish
• "check" reports mismatch_cnt=262272 after 256 MiB of degraded

writes and file contents differ; the second disk's "recovery" completes in milliseconds because everything is skipped

The same conversion in raid1 got it right (still_degraded = true). Restore the correct value.