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sched_ext: Fix premature ops->priv publication in scx_alloc_and_add_sched()

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scx_alloc_and_add_sched() publishes @sch through ops->priv before allocating
the cgroup path. If that allocation fails, the unwind path clears ops->priv
and frees @sch immediately. scx_prog_sched() callers can dereference
ops->priv from RCU context the moment it is set, so freeing without a grace
period can use-after-free a concurrent kfunc caller.

Move the publication below the cgroup path allocation so that every failure
path after publication frees @sch through kobject_put(), whose release path
defers the freeing by a grace period.

Fixes: 105dcd005b ("sched_ext: Introduce scx_prog_sched()")
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo
2026-07-09 11:08:22 -10:00
parent db4e9defd2
commit 49b3378a75
1 changed files with 12 additions and 6 deletions
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18
kernel/sched/ext/ext.c
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@@ -6878,11 +6878,6 @@ static struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
sch->ops = *cmd->ops;
}
rcu_assign_pointer(ops->priv, sch);
sch->kobj.kset = scx_kset;
INIT_LIST_HEAD(&sch->all);
#ifdef CONFIG_EXT_SUB_SCHED
char *buf = kzalloc(PATH_MAX, GFP_KERNEL);
if (!buf) {
@@ -6900,7 +6895,19 @@ static struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
sch->cgrp = cgrp;
INIT_LIST_HEAD(&sch->children);
INIT_LIST_HEAD(&sch->sibling);
#endif /* CONFIG_EXT_SUB_SCHED */
/*
* Publishing makes @sch visible to scx_prog_sched() readers. Failure
* paths after this point must free @sch through kobject_put() whose
* release path defers the actual freeing by an RCU grace period.
*/
rcu_assign_pointer(ops->priv, sch);
sch->kobj.kset = scx_kset;
INIT_LIST_HEAD(&sch->all);
#ifdef CONFIG_EXT_SUB_SCHED
if (parent) {
/*
* Pin @parent for @sch's lifetime. The kobject hierarchy pins
@@ -6955,7 +6962,6 @@ static struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
#ifdef CONFIG_EXT_SUB_SCHED
err_free_lb_resched:
RCU_INIT_POINTER(ops->priv, NULL);
free_cpumask_var(sch->bypass_lb_resched_cpumask);
#endif
err_free_lb_cpumask: