Medium [CVE-2026-64326] skip sync_blockdev on surprise removal in bdev_mark_dead
This medium-severity Red Hat Linux advisory covers CVE-2026-64326 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat package: kernel-rt.
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Summary
In the Linux kernel, the following vulnerability has been resolved: block: skip sync_blockdev() on surprise removal in bdev_mark_dead() bdev_mark_dead()'s @surprise == true means the device is already gone.
The filesystem callback fs_bdev_mark_dead() honours this and skips sync_filesystem(), but the bare block device path (no ->mark_dead op) lost its!surprise guard when the holder ->mark_dead callback was wired up (see Fixes), and now calls sync_blockdev() unconditionally, which can hang forever waiting on writeback that can no longer complete. syzkaller hit this via nvme_reset_work()'s "I/O queues lost" path: nvme_mark_namespaces_dead() -> blk_mark_disk_dead() -> bdev_mark_dead(bdev, true) -> sync_blockdev() blocks in folio_wait_writeback(), wedging the reset worker and every task waiting on it.
Skip the sync on surprise removal, matching fs_bdev_mark_dead(); invalidate_bdev() still runs. Orderly removal (surprise == false) is unchanged.
Found by FuzzNvme(Syzkaller with FEMU fuzzing framework). When a block device is unexpectedly removed, the `bdev_mark_dead()` function can unconditionally attempt to synchronize the device, even if it is no longer present.
This can lead to a system hang, effectively causing a Denial of Service (DoS), as the system waits indefinitely for writeback operations that cannot complete.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.
Official advisory · medium-confidence parse· fetched 27 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists. Confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 27 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That does not mean no fix exists. Read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 27 days ago·verify at source
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