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SubjectRe: [PATCH] arm64/smp: check !ipi_desc[i] in arch_show_interrupts
Date
在 2022/6/9 23:20, Will Deacon 写道:
> On Fri, May 27, 2022 at 08:22:36AM +0000, Chen Jun wrote:
>> There is a potential dereferencing null pointer issue in
>> arch_show_interrupts.
>>
>> Problem 1:
>> int arch_show_interrupts(struct seq_file *p, int prec)
>> for (i = 0; i < NR_IPI; i++) {
>> seq_printf(p, "%10u ", irq_desc_kstat_cpu(ipi_desc[i],
>> cpu));
>>
>> Only ipi_desc[0..nr_ipi - 1] are initialized in set_smp_ipi_range.
>> and ipi_desc[nr_ipi..NR_IPI] are NULL.
>> irq_desc_kstat_cpu will dereference NULL pointer.
>> For now, the problem can not be triggered, because NR_IPI is always
>> equal to nr_ipi.
>>
>> Problem 2:
>> If request_percpu_irq failed in set_smp_ipi_range, ipi_desc[i]
>> would be NULL.
>> irq_desc_kstat_cpu will dereference NULL pointer.
>>
>> check !ipi_desc[i] (as arm does) to avoid the problem.
>>
>> Signed-off-by: Chen Jun <chenjun102@huawei.com>
>> ---
>> arch/arm64/kernel/smp.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
>> index 62ed361a4376..3d54f464428b 100644
>> --- a/arch/arm64/kernel/smp.c
>> +++ b/arch/arm64/kernel/smp.c
>> @@ -781,6 +781,9 @@ int arch_show_interrupts(struct seq_file *p, int prec)
>> unsigned int cpu, i;
>>
>> for (i = 0; i < NR_IPI; i++) {
>> + if (!ipi_desc[i])
>> + continue;
>
> Why not just use nr_ipi instead of NR_IPI?

Yee, that is what I do at first. But I noticed that:

void __init set_smp_ipi_range(int ipi_base, int n)
for (i = 0; i < nr_ipi; i++) {
err = request_percpu_irq(ipi_base + i, ipi_handler,
"IPI", &cpu_number);
WARN_ON(err);
ipi_desc[i] = irq_to_desc(ipi_base + i);

If request_percpu_irq return a error, I not sure if ipi_desc[i] makes sense.

>
> Will
>

--
Regards
Chen Jun

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