CVE-2026-89457: s390/dasd: Guard sysfs discipline callbacks against unallocated private data
In the Linux kernel, the following vulnerability has been resolved:
s390/dasd: Guard sysfs discipline callbacks against unallocated private data
Several sysfs show/store handlers call a discipline callback that dereferences device->private, either directly or through the DASDDEFINEATTR() macro. During dasdgenericsetonline() the discipline is assigned before checkdevice() allocates device->private, so an unprivileged read of one of these world-readable attributes in that window dereferences a NULL pointer and panics.
Guard the dereference inside each callback that actually touches device->private.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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debian/linuxto a version that resolves this vulnerability.Fixed in 6.1.190-1Fixed in 6.12.115-2Fixed in 7.2.12-1Fixed in 7.2.15-1 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1 - Compensating control
In each DASD sysfs show/store callback that directly or indirectly dereferences device->private, including callbacks invoked through the DASD_DEFINE_ATTR() macro, guard the dereference so it is not performed before device->private has been allocated.
Event History
Frequently Asked Questions
Who is exposed to this issue?
Systems using the Linux kernel DASD driver on s390 are exposed during the interval in which a DASD device is being brought online after its discipline is assigned but before its private data is allocated. A local unprivileged user can trigger the issue because the affected sysfs attributes are world-readable.
What does an attacker need to do to exploit it?
An attacker needs local access and must read an affected DASD sysfs attribute during the narrow device-online initialization window. The resulting NULL-pointer dereference can panic the kernel.
Are default permissions sufficient for exploitation?
Yes. The affected attributes are described as world-readable, so exploitation does not require elevated privileges to read them.
What should be done if patching cannot happen immediately?
The provided information does not specify a workaround. Reducing untrusted local access while DASD devices are being brought online may reduce exposure, but the described fix is to guard callbacks that access device private data.