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sched/fair: Fix potential memory corruption in child_cfs_rq_on_list

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[ Upstream commit 3b4035ddbf ]

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: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Zecheng Li 2025-03-04 21:40:31 +00:00 committed by Greg Kroah-Hartman
parent 49bf314771
commit 5cb300dcdd
1 changed files with 4 additions and 2 deletions
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6
kernel/sched/fair.c
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@ -3303,15 +3303,17 @@ 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);