CVE-2025-21919
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk10th percentile - higher than 10% of all known CVEs
Summary
In the Linux kernel scheduler CFS, a potential memory corruption vulnerability was found in the child_cfs_rq_on_list function. The issue stems from an invalid conversion of the 'prev' pointer from the rq's leaf_cfs_rq_list, potentially causing memory faults or garbage data access.
Risk Assessment
The vulnerability may lead to system instability, kernel panic, or unpredictable behavior, especially after changes in kernel data structure layout.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit adding a check of the 'prev' pointer against the rq->leaf_cfs_rq_list).
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Original NVD description (English source)
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 rq's 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 rq's 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.