CVE-2026-90004

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

mm/damon/core: handle region split failure in apply_min_nr_regions()

damon_apply_min_nr_regions() repeatedly split each region until its size

becomes small enough to meet the user-defined low limit of the number of

regions. The loop assumes the split operation (damon_split_region_at())

will always succeed and create the new region. But the operation could

silently fail for memory allocation failures, for example.

If such failure happens and the region was the last region, the linked

list-based next region fetching returns invalid pointer. As a result,

invalid memory dereference and corruption could happen. Even if the

corner case is handled, it imposes stress to the allocator by trying split

regions for other targets. Fix the issue by breaking all the loops for

any region split failure.

This means there could be a min_nr_regions violation. It will only rarely

happen since the allocation is arguably too small to fail. Even if it

happens, it is only temporal. damon_apply_min_nr_regions() will be called

again after the aggregation interval.

The user impact of the issue should be minor, since the allocation is

arguably too small to fail. But, it could still theoretically happen, and

the consequence is very bad.

This issue was discovered [1] by Sashiko.