NULL Pointer Dereference Affecting kernel-rt-modules-extra package, versions *

Note: Versions mentioned in the description apply only to the upstream kernel-rt-modules-extra package and not the kernel-rt-modules-extra package as distributed by Centos. See How to fix? for Centos:8 relevant fixed versions and status.

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

null_blk: fix null-ptr-dereference while configuring 'power' and 'submit_queues'

Writing 'power' and 'submit_queues' concurrently will trigger kernel panic:

Test script:

modprobe null_blk nr_devices=0 mkdir -p /sys/kernel/config/nullb/nullb0 while true; do echo 1 > submit_queues; echo 4 > submit_queues; done & while true; do echo 1 > power; echo 0 > power; done

Test result:

BUG: kernel NULL pointer dereference, address: 0000000000000148 Oops: 0000 [#1] PREEMPT SMP RIP: 0010:__lock_acquire+0x41d/0x28f0 Call Trace: <TASK> lock_acquire+0x121/0x450 down_write+0x5f/0x1d0 simple_recursive_removal+0x12f/0x5c0 blk_mq_debugfs_unregister_hctxs+0x7c/0x100 blk_mq_update_nr_hw_queues+0x4a3/0x720 nullb_update_nr_hw_queues+0x71/0xf0 [null_blk] nullb_device_submit_queues_store+0x79/0xf0 [null_blk] configfs_write_iter+0x119/0x1e0 vfs_write+0x326/0x730 ksys_write+0x74/0x150

This is because del_gendisk() can concurrent with blk_mq_update_nr_hw_queues():

nullb_device_power_store nullb_apply_submit_queues null_del_dev del_gendisk nullb_update_nr_hw_queues if (!dev->nullb) // still set while gendisk is deleted return 0 blk_mq_update_nr_hw_queues dev->nullb = NULL

Fix this problem by resuing the global mutex to protect nullb_device_power_store() and nullb_update_nr_hw_queues() from configfs.

• https://access.redhat.com/security/cve/CVE-2024-36478
• https://git.kernel.org/stable/c/5d0495473ee4c1d041b5a917f10446a22c047f47
• https://git.kernel.org/stable/c/a2db328b0839312c169eb42746ec46fc1ab53ed2
• https://git.kernel.org/stable/c/aaadb755f2d684f715a6eb85cb7243aa0c67dfa9