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sched_ext: Close the pre-enable ops error claim window

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scx_alloc_and_add_sched() publishes ops->priv before
scx_root_enable_workfn() switches the state to SCX_ENABLING. An error
claimed via scx_bpf_error_bstr() from an associated BPF program in that
window is consumed by scx_disable_workfn(), which takes the pre-enable
shortcut in scx_root_disable(). The shortcut returns without any teardown
and restores SCX_DISABLED with an unconditional scx_set_enable_state() xchg
racing the enable workfn's own transition. The enable then completes with
the claim consumed: the scheduler stays up but can never be disabled again,
and bpf_scx_unreg() frees it while still in use, resulting in a
use-after-free. Both WARN_ON_ONCE()s fire back to back:

  WARNING: kernel/sched/ext/ext.c:7522 at
  scx_root_enable_workfn+0xeec/0x1be0, CPU#3: scx_enable_help/276

  WARNING: kernel/sched/ext/ext.c:6398 at scx_root_disable+0xb50/0xdb8,
  CPU#0: sched_ext_helpe/664

scx_root_enable_workfn() switches to SCX_ENABLING before the scheduler
allocation, so ops->priv is never visible while SCX_DISABLED. The allocation
failure path restores SCX_DISABLED.

Fixes: 105dcd005b ("sched_ext: Introduce scx_prog_sched()")
Cc: stable@vger.kernel.org
Signed-off-by: fangqiurong <fangqiurong@kylinos.cn>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
fangqiurong
2026-09-13 05:53:33 -10:00
committed by Tejun Heo
parent 89ff16f071
commit c7a1c6e800
1 changed files with 9 additions and 7 deletions
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kernel/sched/ext/ext.c
+9 -7
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@@ -7516,22 +7516,24 @@ static void scx_root_enable_workfn(struct kthread_work *work)
#ifdef CONFIG_EXT_SUB_SCHED
cgroup_get(cgrp);
#endif
/*
* Transition to ENABLING to arm the disable path. Allocation failure
* still unwinds locally. Full disabling on failure applies only after
* scx_alloc_and_add_sched() succeeds.
*/
WARN_ON_ONCE(scx_set_enable_state(SCX_ENABLING) != SCX_DISABLED);
WARN_ON_ONCE(scx_root);
sch = scx_alloc_and_add_sched(cmd, cgrp, NULL);
if (IS_ERR(sch)) {
ret = PTR_ERR(sch);
WARN_ON_ONCE(scx_set_enable_state(SCX_DISABLED) != SCX_ENABLING);
goto err_free_tid_hash;
}
if (sch->is_cid_type)
static_branch_enable(&__scx_is_cid_type);
/*
* Transition to ENABLING and clear exit info to arm the disable path.
* Failure triggers full disabling from here on.
*/
WARN_ON_ONCE(scx_set_enable_state(SCX_ENABLING) != SCX_DISABLED);
WARN_ON_ONCE(scx_root);
atomic_long_set(&scx_nr_rejected, 0);
for_each_possible_cpu(cpu) {