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

mm: fix NULL pointer dereference in alloc_pages_bulk_noprof

We triggered a NULL pointer dereference for ac.preferred_zoneref->zone in
alloc_pages_bulk_noprof() when the task is migrated between cpusets.

When cpuset is enabled, in prepare_alloc_pages(), ac->nodemask may be
&current->mems_allowed.  when first_zones_zonelist() is called to find
preferred_zoneref, the ac->nodemask may be modified concurrently if the
task is migrated between different cpusets.  Assuming we have 2 NUMA Node,
when traversing Node1 in ac->zonelist, the nodemask is 2, and when
traversing Node2 in ac->zonelist, the nodemask is 1.  As a result, the
ac->preferred_zoneref points to NULL zone.

In alloc_pages_bulk_noprof(), for_each_zone_zonelist_nodemask() finds a
allowable zone and calls zonelist_node_idx(ac.preferred_zoneref), leading
to NULL pointer dereference.

__alloc_pages_noprof() fixes this issue by checking NULL pointer in commit
ea57485af8f4 ("mm, page_alloc: fix check for NULL preferred_zone") and
commit df76cee6bbeb ("mm, page_alloc: remove redundant checks from alloc
fastpath").

To fix it, check NULL pointer for preferred_zoneref->zone.

https://git.kernel.org/stable/c/31502374627ba9ec3e710dbd0bb00457cc6d2c19

https://git.kernel.org/stable/c/6addb2d9501ec866d7b3a3b4e665307c437e9be2

https://git.kernel.org/stable/c/8ce41b0f9d77cca074df25afd39b86e2ee3aa68e

https://git.kernel.org/stable/c/d0f16cec79774c3132df006cf771eddd89d08f58