CVE-2026-89457

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 DASD_DEFINE_ATTR() macro. During dasd_generic_set_online() the discipline is assigned before check_device() 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.