null_blk: serialize configfs attribute updates with device setup

Summary

In the Linux kernel, the following vulnerability has been resolved: null_blk: serialize configfs attribute updates with device setup The attribute store methods generated with NULLB_DEVICE_ATTR() refuse to change the configuration of a live device by testing NULLB_DEV_FL_CONFIGURED, but that flag is only set by nullb_device_power_store() after null_add_dev() has returned, and the store methods take no lock at all. configfs only serializes writes to the same open file (buffer->mutex), so a write to any attribute can run concurrently with null_add_dev() and change the device configuration while it is being used. null_add_dev() reads the configuration several times, e.g. dev->zoned is read once to set up the queue limits and once to initialize the zone resources: CPU0: echo 1 > nullb0/power CPU1: echo 1 > nullb0/zoned nullb_device_power_store() mutex_lock(&lock) null_add_dev() if (dev->zoned) -> false /* no BLK_FEAT_ZONED */ nullb_device_zoned_store() test_bit(FL_CONFIGURED) -> 0 dev->zoned = true blk_mq_alloc_disk() /* queue is not zoned */ if (nullb->dev->zoned) -> true null_register_zoned_dev() blk_revalidate_disk_zones() blk_revalidate_disk_zones() is then called for a queue that does not have BLK_FEAT_ZONED set, which triggers its WARN_ON_ONCE() and fails the device setup with -EIO: WARNING: CPU: 2 PID: 322 at block/blk-zoned.c:2357 blk_revalidate_disk_zones+0x4c/0x560 Clearing dev->zoned in the same window is worse: the queue is created with BLK_FEAT_ZONED but the zone resources are never initialized, so add_disk() succeeds for a zoned disk that has no zones. And a store that lands after the last dev->zoned test leaves dev->zoned set while dev->zones is still NULL, which null_process_zoned_cmd() dereferences on the first write. Fix this by taking the global lock, which nullb_device_power_store() already holds across null_add_dev() and null_del_dev(), around both the NULLB_DEV_FL_CONFIGURED test and the update of the device configuration. The submit_queues and poll_queues apply callbacks are now called with that lock held, so remove the locking they did themselves. Since the store methods can run as soon as configfs_register_subsystem() returns, that is, before null_init() gets to mutex_init(&lock), also initialize the lock statically with DEFINE_MUTEX().

Timeline

1. Sep 17, 2026, 4:07 PM UTCCVE published
2. Oct 19, 2026, 8:59 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa · fixed in 6352e7ead2d8111802a554eeb94886f5a9894bb9; From 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa · fixed in 7de792b4c48fba02a36a8077032f7d5093c925e5; From 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa · fixed in aed8af338a09a64d63b068a803c4ecfc5701dd4c; From 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa · fixed in 32456a85995579e56c60cc53c357cda75a9d4f7c; From 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa · fixed in d3d35dd045a35991bf6fd13de5f293e6dd7bf3b3; From 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa · fixed in 4e1f23f9c33c156be7e313b40695af5a3a834739

• Linux Linux

  4.14

• KernelLinux

  From 4.14.0 · fixed in 6.1.188; From 6.2.0 · fixed in 6.6.157; From 6.7.0 · fixed in 6.12.110; From 6.13.0 · fixed in 6.18.52; From 6.19.0 · fixed in 7.2.6

References 6