6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Zecheng Li zecheng@google.com
[ Upstream commit 3b4035ddbfc8e4521f85569998a7569668cccf51 ]
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: fdaba61ef8a2 ("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 --- kernel/sched/fair.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 726fa69c4d88b..2808dbdd03847 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4118,15 +4118,17 @@ 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);