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Date: Fri, 21 Jun 2024 12:19:38 +0200
From: Greg Kroah-Hartman <>
Cc: Greg Kroah-Hartman <>
Subject: CVE-2024-36478: null_blk: fix null-ptr-dereference while configuring 'power' and 'submit_queues'


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

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:
 nullb_update_nr_hw_queues+0x71/0xf0 [null_blk]
 nullb_device_submit_queues_store+0x79/0xf0 [null_blk]

This is because del_gendisk() can concurrent with

nullb_device_power_store	nullb_apply_submit_queues
				  if (!dev->nullb)
				  // still set while gendisk is deleted
				   return 0
 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.

The Linux kernel CVE team has assigned CVE-2024-36478 to this issue.

Affected and fixed versions

	Issue introduced in 5.5 with commit 45919fbfe1c4 and fixed in 6.9.4 with commit 5d0495473ee4
	Issue introduced in 5.5 with commit 45919fbfe1c4 and fixed in 6.10-rc1 with commit a2db328b0839

Please see for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files

The file(s) affected by this issue are:


The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:

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