From: Peter Zijlstra peterz@infradead.org
mainline inclusion from mainline-v5.13-rc1 commit 3a7956e25e1d7b3c148569e78895e1f3178122a9 bugzilla: 52510 https://gitee.com/openeuler/kernel/issues/I4DDEL
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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The kthread_is_per_cpu() construct relies on only being called on PF_KTHREAD tasks (per the WARN in to_kthread). This gives rise to the following usage pattern:
if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p))
However, as reported by syzcaller, this is broken. The scenario is:
CPU0 CPU1 (running p)
(p->flags & PF_KTHREAD) // true
begin_new_exec() me->flags &= ~(PF_KTHREAD|...); kthread_is_per_cpu(p) to_kthread(p) WARN(!(p->flags & PF_KTHREAD) <-- *SPLAT*
Introduce __to_kthread() that omits the WARN and is sure to check both values.
Use this to remove the problematic pattern for kthread_is_per_cpu() and fix a number of other kthread_*() functions that have similar issues but are currently not used in ways that would expose the problem.
Notably kthread_func() is only ever called on 'current', while kthread_probe_data() is only used for PF_WQ_WORKER, which implies the task is from kthread_create*().
Fixes: ac687e6e8c26 ("kthread: Extract KTHREAD_IS_PER_CPU") Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Valentin Schneider Valentin.Schneider@arm.com Link: https://lkml.kernel.org/r/YH6WJc825C4P0FCK@hirez.programming.kicks-ass.net Signed-off-by: Zheng Zucheng zhengzucheng@huawei.com
Conflicts: kernel/sched/core.c Reviewed-by: Chen Hui judy.chenhui@huawei.com Signed-off-by: Chen Jun chenjun102@huawei.com --- kernel/kthread.c | 33 +++++++++++++++++++++++++++------ kernel/sched/fair.c | 2 +- 2 files changed, 28 insertions(+), 7 deletions(-)
diff --git a/kernel/kthread.c b/kernel/kthread.c index 9825cf89c614..508fe5278285 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -84,6 +84,25 @@ static inline struct kthread *to_kthread(struct task_struct *k) return (__force void *)k->set_child_tid; }
+/* + * Variant of to_kthread() that doesn't assume @p is a kthread. + * + * Per construction; when: + * + * (p->flags & PF_KTHREAD) && p->set_child_tid + * + * the task is both a kthread and struct kthread is persistent. However + * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and + * begin_new_exec()). + */ +static inline struct kthread *__to_kthread(struct task_struct *p) +{ + void *kthread = (__force void *)p->set_child_tid; + if (kthread && !(p->flags & PF_KTHREAD)) + kthread = NULL; + return kthread; +} + void free_kthread_struct(struct task_struct *k) { struct kthread *kthread; @@ -168,8 +187,9 @@ EXPORT_SYMBOL_GPL(kthread_freezable_should_stop); */ void *kthread_func(struct task_struct *task) { - if (task->flags & PF_KTHREAD) - return to_kthread(task)->threadfn; + struct kthread *kthread = __to_kthread(task); + if (kthread) + return kthread->threadfn; return NULL; } EXPORT_SYMBOL_GPL(kthread_func); @@ -199,10 +219,11 @@ EXPORT_SYMBOL_GPL(kthread_data); */ void *kthread_probe_data(struct task_struct *task) { - struct kthread *kthread = to_kthread(task); + struct kthread *kthread = __to_kthread(task); void *data = NULL;
- copy_from_kernel_nofault(&data, &kthread->data, sizeof(data)); + if (kthread) + copy_from_kernel_nofault(&data, &kthread->data, sizeof(data)); return data; }
@@ -514,9 +535,9 @@ void kthread_set_per_cpu(struct task_struct *k, int cpu) set_bit(KTHREAD_IS_PER_CPU, &kthread->flags); }
-bool kthread_is_per_cpu(struct task_struct *k) +bool kthread_is_per_cpu(struct task_struct *p) { - struct kthread *kthread = to_kthread(k); + struct kthread *kthread = __to_kthread(p); if (!kthread) return false;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index bd42f8e9f5ad..32fea109e604 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7804,7 +7804,7 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) return 0;
/* Disregard pcpu kthreads; they are where they need to be. */ - if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p)) + if (kthread_is_per_cpu(p)) return 0;
if (!cpumask_test_cpu(env->dst_cpu, p->cpus_ptr)) {