CVE-2026-64326block: skip sync_blockdev() on surprise removal in bdev_mark_dead()

Official description

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).

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/d6998ddd507c81e3829489a6ead23f17f5acb7fe
• https://git.kernel.org/stable/c/f41cf35ee2a1e31374b3f54e7579c55153506e70
• https://git.kernel.org/stable/c/9818bcae3c0ca1dde4b9a334125c46676e0a9b29
• https://git.kernel.org/stable/c/aa4c4a9315764b2b7a7182e72cc5ea87520436b4
• https://git.kernel.org/stable/c/49f06cff50a4ccf3b7a1a662ceb892b3b21a527a