CVE-2026-64416

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

mm: swap_cgroup: fix NULL deref in lookup_swap_cgroup_id on swapless host

lookup_swap_cgroup_id() passes swap_cgroup_ctrl[type].map to

__swap_cgroup_id_lookup() without checking that the type was ever

registered via swap_cgroup_swapon(). On a swapless host every ctrl->map

is NULL, so __swap_cgroup_id_lookup() dereferences NULL + a scaled

swp_offset().

Since commit bea67dcc5eea ("mm: attempt to batch free swap entries for

zap_pte_range()"), zap_pte_range() -> swap_pte_batch() calls

lookup_swap_cgroup_id() on any non-present, non-none PTE that decodes as a

real swap entry, without first validating it against swap_info[]. A

single PTE corrupted into a type-0 swap entry takes the host down at

process exit.

We hit this in production on a swapless 6.12.58 host: ~1s of

"get_swap_device: Bad swap file entry 3f800204222bb" (do_swap_page() being

correctly defensive about the same entry) followed by

BUG: unable to handle page fault for address: 000003f800204220

RIP: 0010:lookup_swap_cgroup_id+0x2b/0x60

Call Trace:

swap_pte_batch+0xbf/0x230

zap_pte_range+0x4c8/0x780

unmap_page_range+0x190/0x3e0

exit_mmap+0xd9/0x3c0

do_exit+0x20c/0x4b0

syzbot has reported the identical stack.

The source of the PTE corruption is a separate bug; this change makes the

teardown path as robust as the fault path already is. Every other caller

of lookup_swap_cgroup_id() is downstream of a get_swap_device() that has

already validated the entry, so the new branch is cold.