Re:Re:[PATCH 6/6] irq: Potentially 'offset out of size' bug

Re:Re:[PATCH 6/6] irq: Potentially 'offset out of size' bug

[Jiasheng Jiang]

> On Fri, Sep 10 2021 at 03:26, Jiasheng Jiang wrote:
> The find_next_bit() use nr_irqs as size, and using it without
> any check might cause its returned value out of the sizei

On Fri, Sep 10 2021 at 18:28, tglx wrote:
> Why exactly is this a problem? The return value has to be checked at the
> call site anyway.

There is really a check at the call site, but the annotation of the 
irq_get_next_irq() is 'Returns next irq number after offset or nr_irqs 
if none is found', which tells the programmer should not check the
return value of it. In case of a programmer write a new call for the
irq_get_next_irq(), he may not check the return value because of the 
annotation said. Therefore, it had better to add the check inside of
irq_get_next_irq() to fit for the annotation.

Thanks,

        Jiasheng Jiang

Re:Re:[PATCH 6/6] irq: Potentially 'offset out of size' bug

[Thomas Gleixner]

On Tue, Sep 14 2021 at 08:48, Jiasheng Jiang wrote:
>> On Fri, Sep 10 2021 at 03:26, Jiasheng Jiang wrote:
>> The find_next_bit() use nr_irqs as size, and using it without
>> any check might cause its returned value out of the sizei
>
> On Fri, Sep 10 2021 at 18:28, tglx wrote:
>> Why exactly is this a problem? The return value has to be checked at the
>> call site anyway.
>
> There is really a check at the call site, but the annotation of the 
> irq_get_next_irq() is 'Returns next irq number after offset or nr_irqs 
> if none is found', which tells the programmer should not check the
> return value of it. In case of a programmer write a new call for the
> irq_get_next_irq(), he may not check the return value because of the 
> annotation said.

The return value has always to be checked because nr_irqs is guaranteed
to be an invalid index.

> Therefore, it had better to add the check inside of irq_get_next_irq()
> to fit for the annotation.

Care to look what find_next_bit(..., size) does?

    * Returns the bit number for the next set bit
    * If no bits are set, returns @size.

So for:

    res = find_next_bit(addr, size, offset);

res is guaranteed to be:

    offset < res <= size

IOW. irq_get_next_irq() is doing exactly what the comment says.

So again, which problem are you trying to solve?

Thanks,

        tglx