netdev - Re: [PATCH net-next] net: ipa: don't proceed to out-of-bound write

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Date:   Wed, 18 May 2022 20:22:46 -0500
From:   Alex Elder <elder@...e.org>
To:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, pabeni@...hat.com,
        elder@...nel.org
Subject: Re: [PATCH net-next] net: ipa: don't proceed to out-of-bound write

On 5/18/22 7:44 PM, Jakub Kicinski wrote:
> GCC 12 seems upset that we check ipa_irq against array bound
> but then proceed, anyway:
> 
> drivers/net/ipa/ipa_interrupt.c: In function ‘ipa_interrupt_add’:
> drivers/net/ipa/ipa_interrupt.c:196:27: warning: array subscript 30 is above array bounds of ‘void (*[30])(struct ipa *, enum ipa_irq_id)’ [-Warray-bounds]
>    196 |         interrupt->handler[ipa_irq] = handler;
>        |         ~~~~~~~~~~~~~~~~~~^~~~~~~~~
> drivers/net/ipa/ipa_interrupt.c:42:27: note: while referencing ‘handler’
>     42 |         ipa_irq_handler_t handler[IPA_IRQ_COUNT];
>        |                           ^~~~~~~
> 
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>

Well, that's a reasonable thing to complain about.  I think when
I switched to using these WARN*() calls Leon said testing the
return value was unusual in the networking code.

In any case, this is a good fix.  The problem won't happen
anyway, so silencing the error this way is just fine.

Reviewed-by: Alex Elder <elder@...aro.org>

> ---
> CC: elder@...nel.org
> ---
>   drivers/net/ipa/ipa_interrupt.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ipa/ipa_interrupt.c b/drivers/net/ipa/ipa_interrupt.c
> index b35170a93b0f..307bed2ee707 100644
> --- a/drivers/net/ipa/ipa_interrupt.c
> +++ b/drivers/net/ipa/ipa_interrupt.c
> @@ -191,7 +191,8 @@ void ipa_interrupt_add(struct ipa_interrupt *interrupt,
>   	struct ipa *ipa = interrupt->ipa;
>   	u32 offset;
>   
> -	WARN_ON(ipa_irq >= IPA_IRQ_COUNT);
> +	if (WARN_ON(ipa_irq >= IPA_IRQ_COUNT))
> +		return;
>   
>   	interrupt->handler[ipa_irq] = handler;
>   
> @@ -208,7 +209,8 @@ ipa_interrupt_remove(struct ipa_interrupt *interrupt, enum ipa_irq_id ipa_irq)
>   	struct ipa *ipa = interrupt->ipa;
>   	u32 offset;
>   
> -	WARN_ON(ipa_irq >= IPA_IRQ_COUNT);
> +	if (WARN_ON(ipa_irq >= IPA_IRQ_COUNT))
> +		return;
>   
>   	/* Update the IPA interrupt mask to disable it */
>   	interrupt->enabled &= ~BIT(ipa_irq);