CVE-2026-98400

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, reipl type init() selects IPL TYPE UNKNOWN, and reipl block actual remains NULL.

kdump passes the re-IPL parameter block to the dump kernel through os info. Before commit 3b9678472bab ("s390/ipl: correct kdump reipl block checksum calculation"), the os info entry was added only for IPL types which initialized reipl block actual. That commit moved the os info update to machine crash shutdown(), making it unconditional. As a result, set os info reipl block() dereferences reipl block actual for IPL TYPE UNKNOWN. This may happen to work by chance when address zero contains readable lowcore data and the resulting empty os info entry is ignored by the dump kernel.

Skip the os info update when no re-IPL parameter block is available. Kdump then collect the dump and reboot without setting re-IPL parameter block.