Subject: Re: [PATCH] pcmcia: avoid buffer overflow in pcmcia_setup_isa_irq

From: Christoph Fritz <[email-masked]>
Date: Tue, 03 Aug 2010 12:26:08 +0200

On Tue, 2010-08-03 at 09:40 +0200, Dominik Brodowski wrote:
> On Tue, Aug 03, 2010 at 02:38:19AM +0200, Christoph Fritz wrote:
> > Hi,
> > 
> > buffer overflow in next-tree's commit 6f0f38c45a8f2f511c25893e33011ff32fc811db:
> >  size of array pcmcia_used_irq[] can be less than 32
> > 
> > in drivers/pcmcia/pcmcia_resource.c
> >    +static int pcmcia_setup_isa_irq(struct pcmcia_device *p_dev, int type)
> >    +{
> >    [..]
> >    +       for (try = 0; try < 64; try++) {
> >    +               irq = try % 32;
> >    [..]
> >    +
> >    +               /* avoid an IRQ which is already used by another PCMCIA card */
> >    +               if ((try < 32) && pcmcia_used_irq[irq])
> >    +                       continue;
> > 
> > drivers/pcmcia/pcmcia_resource.c
> >    static u8 pcmcia_used_irq[NR_IRQS];
> > 
> > arch/x86/include/asm/irq_vectors.h
> >    #define NR_IRQS_LEGACY                    16
> >    [..]
> >    #else /* !CONFIG_X86_IO_APIC: */
> >    # define NR_IRQS                        NR_IRQS_LEGACY
> >    #endif
> > 
> > ---
> > non-tested fix:
> 
> What about this?
> 
> 
> [PATCH] pcmcia: avoid buffer overflow in pcmcia_setup_isa_irq
> 
> NR_IRQS may be as low as 16, causing a (harmless?) buffer overflow in
> pcmcia_setup_isa_irq():
> 
> static u8 pcmcia_used_irq[NR_IRQS];
> 
> ...
> 
> 		if ((try < 32) && pcmcia_used_irq[irq])
> 			continue;
> 
> This is read-only, so if this address would be non-zero, it would just
> mean we would not attempt an IRQ >= NR_IRQS -- which would fail anyway!
> And as request_irq() fails for an irq >= NR_IRQS, the setting code path:
> 
> 			pcmcia_used_irq[irq]++;
> 
> is never reached as well.
> 
> Reported-by: Christoph Fritz <[email-masked]>
> CC: [email-masked]
> Signed-off-by: Dominik Brodowski <[email-masked]>
> 
> diff --git a/drivers/pcmcia/pcmcia_resource.c b/drivers/pcmcia/pcmcia_resource.c
> index d48437f..54aa1c2 100644
> --- a/drivers/pcmcia/pcmcia_resource.c
> +++ b/drivers/pcmcia/pcmcia_resource.c
> @@ -677,7 +677,7 @@ EXPORT_SYMBOL(__pcmcia_request_exclusive_irq);
>  #ifdef CONFIG_PCMCIA_PROBE
>  
>  /* mask of IRQs already reserved by other cards, we should avoid using them */
> -static u8 pcmcia_used_irq[NR_IRQS];
> +static u8 pcmcia_used_irq[32];
>  
>  static irqreturn_t test_action(int cpl, void *dev_id)
>  {
> @@ -700,6 +700,9 @@ static int pcmcia_setup_isa_irq(struct pcmcia_device *p_dev, int type)
>  	for (try = 0; try < 64; try++) {
>  		irq = try % 32;
>  
> +		if (irq > NR_IRQS)
> +			continue;
> +
>  		/* marked as available by driver, not blocked by userspace? */
>  		if (!((mask >> irq) & 1))
>  			continue;

thanks,
 you can add a

Signed-off-by: Christoph Fritz <[email-masked]>