CVE-2026-64416

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> mm: swap_cgroup: fix NULL deref in lookup_swap_cgroup_id on swapless host<br /> <br /> lookup_swap_cgroup_id() passes swap_cgroup_ctrl[type].map to<br /> __swap_cgroup_id_lookup() without checking that the type was ever<br /> registered via swap_cgroup_swapon(). On a swapless host every ctrl-&gt;map<br /> is NULL, so __swap_cgroup_id_lookup() dereferences NULL + a scaled<br /> swp_offset().<br /> <br /> Since commit bea67dcc5eea ("mm: attempt to batch free swap entries for<br /> zap_pte_range()"), zap_pte_range() -&gt; swap_pte_batch() calls<br /> lookup_swap_cgroup_id() on any non-present, non-none PTE that decodes as a<br /> real swap entry, without first validating it against swap_info[]. A<br /> single PTE corrupted into a type-0 swap entry takes the host down at<br /> process exit.<br /> <br /> We hit this in production on a swapless 6.12.58 host: ~1s of<br /> "get_swap_device: Bad swap file entry 3f800204222bb" (do_swap_page() being<br /> correctly defensive about the same entry) followed by<br /> <br /> BUG: unable to handle page fault for address: 000003f800204220<br /> RIP: 0010:lookup_swap_cgroup_id+0x2b/0x60<br /> Call Trace:<br /> swap_pte_batch+0xbf/0x230<br /> zap_pte_range+0x4c8/0x780<br /> unmap_page_range+0x190/0x3e0<br /> exit_mmap+0xd9/0x3c0<br /> do_exit+0x20c/0x4b0<br /> <br /> syzbot has reported the identical stack.<br /> <br /> The source of the PTE corruption is a separate bug; this change makes the<br /> teardown path as robust as the fault path already is. Every other caller<br /> of lookup_swap_cgroup_id() is downstream of a get_swap_device() that has<br /> already validated the entry, so the new branch is cold.