CVE-2025-21919

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

sched/fair: Fix potential memory corruption in child_cfs_rq_on_list

child_cfs_rq_on_list attempts to convert a prev pointer to a cfs_rq. This prev pointer can originate from struct rqs leaf_cfs_rq_list, making the conversion invalid and potentially leading to memory corruption. Depending on the relative positions of leaf_cfs_rq_list and the task group (tg) pointer within the struct, this can cause a memory fault or access garbage data.

The issue arises in list_add_leaf_cfs_rq, where both cfs_rq->leaf_cfs_rq_list and rq->leaf_cfs_rq_list are added to the same leaf list. Also, rq->tmp_alone_branch can be set to rq->leaf_cfs_rq_list.

This adds a check if (prev == &rq->leaf_cfs_rq_list) after the main conditional in child_cfs_rq_on_list. This ensures that the container_of operation will convert a correct cfs_rq struct.

This check is sufficient because only cfs_rqs on the same CPU are added to the list, so verifying the prev pointer against the current rqs list head is enough.

Fixes a potential memory corruption issue that due to current struct layout might not be manifesting as a crash but could lead to unpredictable behavior when the layout changes.

Affected Software

References

• https://git.kernel.org/stable/c/000c9ee43928f2ce68a156dd40bab7616256f4dd
• https://git.kernel.org/stable/c/3b4035ddbfc8e4521f85569998a7569668cccf51
• https://git.kernel.org/stable/c/5cb300dcdd27e6a351ac02541e0231261c775852
• https://git.kernel.org/stable/c/9cc7f0018609f75a349e42e3aebc3b0e905ba775
• https://git.kernel.org/stable/c/b5741e4b9ef3567613b2351384f91d3f16e59986
• https://git.kernel.org/stable/c/e1dd09df30ba86716cb2ffab97dc35195c01eb8f