CVE-2026-98400s390/ipl: Fix NULL deref in kdump without re-IPL parm block

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/030e88812435fc5d6aa42eee41fa77b5ea620327
• https://git.kernel.org/stable/c/92d0829eae257544b6b0faccb6e7079c45e22d48
• https://git.kernel.org/stable/c/50f9c40768e84f30d374235b3ee3850a94d9ac29
• https://git.kernel.org/stable/c/b6bf82bc5e00afaf836f8bb9a676bffc182a6bbd
• https://git.kernel.org/stable/c/7f918871112e8e7c581e99eb8e545af4e59c8367