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Merge: CVE-2025-21919: sched/fair: Fix potential memory corruption in child_cfs_rq_on_list 

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/6799

JIRA: https://issues.redhat.com/browse/RHEL-88083
CVE: CVE-2025-21919

```
commit 3b4035ddbfc8e4521f85569998a7569668cccf51
Author: Zecheng Li <zecheng@google.com>
Date:   Tue Mar 4 21:40:31 2025 +0000

    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.

    Fixes: fdaba61ef8 ("sched/fair: Ensure that the CFS parent is added after unthrottling")
    Signed-off-by: Zecheng Li <zecheng@google.com>
    Reviewed-and-tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
    Link: https://lore.kernel.org/r/20250304214031.2882646-1-zecheng@google.com```

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

---

<small>Created 2025-04-29 13:27 UTC by backporter - [KWF FAQ](https://red.ht/kernel_workflow_doc) - [Slack #team-kernel-workflow](https://redhat-internal.slack.com/archives/C04LRUPMJQ5) - [Source](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/webhook/utils/backporter.py) - [Documentation](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/docs/README.backporter.md) - [Report an issue](https://issues.redhat.com/secure/CreateIssueDetails!init.jspa?pid=12334433&issuetype=1&priority=4&summary=backporter+webhook+issue&components=kernel-workflow+/+backporter)</small>

Approved-by: Phil Auld <pauld@redhat.com>
Approved-by: Xiubo Li <xiubli@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Augusto Caringi <acaringi@redhat.com>
This commit is contained in:
Augusto Caringi 2025-07-21 18:52:54 -03:00
parent b4d1a37187 cbcf831332
commit bdb8764f6f
1 changed files with 4 additions and 2 deletions
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6
kernel/sched/fair.c
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@ -3708,15 +3708,17 @@ static inline bool child_cfs_rq_on_list(struct cfs_rq *cfs_rq)
{
struct cfs_rq *prev_cfs_rq;
struct list_head *prev;
struct rq *rq = rq_of(cfs_rq);
if (cfs_rq->on_list) {
prev = cfs_rq->leaf_cfs_rq_list.prev;
} else {
struct rq *rq = rq_of(cfs_rq);
prev = rq->tmp_alone_branch;
}
if (prev == &rq->leaf_cfs_rq_list)
return false;
prev_cfs_rq = container_of(prev, struct cfs_rq, leaf_cfs_rq_list);
return (prev_cfs_rq->tg->parent == cfs_rq->tg);