linux-kernel - Re: [PATCH] irq/irq_domain: Quit ignoring error returns from irq_alloc_desc

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Date:	Fri, 06 Apr 2012 18:26:16 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	David Daney <ddaney.cavm@...il.com>,
	devicetree-discuss@...ts.ozlabs.org,
	Rob Herring <rob.herring@...xeda.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH] irq/irq_domain: Quit ignoring error returns from irq_alloc_desc_from().

On Thu,  5 Apr 2012 16:52:13 -0700, David Daney <ddaney.cavm@...il.com> wrote:
> From: David Daney <david.daney@...ium.com>
> 
> In commit 4bbdd45a (irq_domain/powerpc: eliminate irq_map; use
> irq_alloc_desc() instead) code was added that ignores error returns
> from irq_alloc_desc_from() by (silently) casting the return value to
> unsigned.  The negitive value error return now suddenly looks like a
> valid irq number.
> 
> Commits cc79ca69 (irq_domain: Move irq_domain code from powerpc to
> kernel/irq) and 1bc04f2c (irq_domain: Add support for base irq and
> hwirq in legacy mappings) move this code to its current location in
> irqdomain.c
> 
> The result of all of this is a null pointer dereference OOPS if one of
> the error cases is hit.
> 
> The fix: Don't cast away the negativeness of the return value and then
> check for errors.
> 
> Signed-off-by: David Daney <david.daney@...ium.com>
> ---
>  kernel/irq/irqdomain.c |   11 ++++++-----
>  1 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
> index af48e59..9d3e3ae 100644
> --- a/kernel/irq/irqdomain.c
> +++ b/kernel/irq/irqdomain.c
> @@ -351,6 +351,7 @@ unsigned int irq_create_mapping(struct irq_domain *domain,
>  				irq_hw_number_t hwirq)
>  {
>  	unsigned int virq, hint;
> +	int irq;

Merged, but I've dropped the new variable in favour of making virq an
int.  Makes for a smaller diffstat.

g.

>  
>  	pr_debug("irq: irq_create_mapping(0x%p, 0x%lx)\n", domain, hwirq);
>  
> @@ -380,14 +381,14 @@ unsigned int irq_create_mapping(struct irq_domain *domain,
>  	hint = hwirq % irq_virq_count;
>  	if (hint == 0)
>  		hint++;
> -	virq = irq_alloc_desc_from(hint, 0);
> -	if (!virq)
> -		virq = irq_alloc_desc_from(1, 0);
> -	if (!virq) {
> +	irq = irq_alloc_desc_from(hint, 0);
> +	if (irq <= 0)
> +		irq = irq_alloc_desc_from(1, 0);
> +	if (irq <= 0) {
>  		pr_debug("irq: -> virq allocation failed\n");
>  		return 0;
>  	}
> -
> +	virq = irq;
>  	if (irq_setup_virq(domain, virq, hwirq)) {
>  		if (domain->revmap_type != IRQ_DOMAIN_MAP_LEGACY)
>  			irq_free_desc(virq);
> -- 
> 1.7.2.3
> 

-- 
Grant Likely, B.Sc, P.Eng.
Secret Lab Technologies,Ltd.
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