CVE-2026-99086: dm-integrity: validate the superblock on resume

In the Linux kernel, the following vulnerability has been resolved:

dm-integrity: validate the superblock on resume

dmintegrityresume() re-reads the superblock from the device so that it picks up the flags and the recalculate position. It performs no validation on the result, while the constructor validates the superblock it reads and sizes all the in-memory structures according to it. The user may modify the superblock on the underlying device while the dm-integrity device is suspended, so that the two no longer agree.

In particular, accessjournaldata() shifts the journal entry index by ic->sb->log2sectorsperblock, while ic->journalsectionsectors and the journal page list were computed with the value that was present at constructor time. Increasing log2sectorsperblock makes the index run past the end of the journal, and dm-integrity then writes 512 bytes through lowmempageaddress(NULL).

Snapshot the validated superblock in the constructor and refuse to resume if any of the fields that describe the on-disk geometry changed.