UBUNTU-CVE-2026-98400: Low severity ubuntu/linux-hwe-edge vulnerability

In the Linux kernel, the following vulnerability has been resolved: s390/ipl: Fix NULL deref in kdump without re-IPL parm block Some IPL types, like HMC FTP boot or QEMU direct kernel boot, might not provide an IPL parameter block. In this case, reipltypeinit() selects IPLTYPEUNKNOWN, and reiplblockactual remains NULL. kdump passes the re-IPL parameter block to the dump kernel through osinfo. Before commit 3b9678472bab ("s390/ipl: correct kdump reipl block checksum calculation"), the osinfo entry was added only for IPL types which initialized reiplblockactual. That commit moved the osinfo update to machinecrashshutdown(), making it unconditional. As a result, setosinforeiplblock() dereferences reiplblockactual for IPLTYPEUNKNOWN. This may happen to work by chance when address zero contains readable lowcore data and the resulting empty osinfo entry is ignored by the dump kernel. Skip the osinfo update when no re-IPL parameter block is available. Kdump then collect the dump and reboot without setting re-IPL parameter block.