CVE-2026-64289: iommufd: Set upper bounds on cache invalidation entry_num and entry_len

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

iommufd: Set upper bounds on cache invalidation entrynum and entrylen

iommufdhwptinvalidate() takes a user-controlled entrynum and entrylen, each bounded only by U32MAX. An entrylen beyond the kernel's struct size makes the copy helper verify the extra bytes are zero, scanning that excess in one uninterruptible pass; a multi-gigabyte value over zeroed user memory trips the soft-lockup watchdog.

A large entrynum is the other half, driving the backend invalidation loop with no reschedule. The VT-d nested handler, for one, copies each entry and flushes caches per iteration, pinning the CPU on a non-preemptible kernel.

Cap both in the ioctl. entrylen is held under PAGESIZE, above any request struct, and entrynum under 1 << 19, the order of a hardware invalidation queue and well beyond any real batch, bounding the per-call loop length.