netdev - Re: [patch] isdn: fix a wrapping bug in isdn_ppp

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Date:	Wed, 10 Oct 2012 06:00:07 -0700
From:	Joe Perches <joe@...ches.com>
To:	Andreas Schwab <schwab@...ux-m68k.org>
Cc:	Dan Carpenter <dan.carpenter@...cle.com>,
	Karsten Keil <isdn@...ux-pingi.de>,
	"David S. Miller" <davem@...emloft.net>,
	Masanari Iida <standby24x7@...il.com>, netdev@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] isdn: fix a wrapping bug in isdn_ppp_ioctl()

On Wed, 2012-10-10 at 14:05 +0200, Andreas Schwab wrote:
> Joe Perches <joe@...ches.com> writes:
> 
> > @@ -589,16 +589,15 @@ isdn_ppp_ioctl(int min, struct file *file, unsigned int cmd, unsigned long arg)
> >  		break;
> >  	case PPPIOCGCOMPRESSORS:
> >  	{
> > -		unsigned long protos[8] = {0,};
> > +		DECLARE_BITMAP(protos, BITS_PER_LONG * 8) = { 0, };
> >  		struct isdn_ppp_compressor *ipc = ipc_head;
> > +
> >  		while (ipc) {
> > -			j = ipc->num / (sizeof(long) * 8);
> > -			i = ipc->num % (sizeof(long) * 8);
> > -			if (j < 8)
> > -				protos[j] |= (0x1 << i);
> > +			if (ipc->num < BITS_PER_LONG * 8)
> > +				set_bit(ipc->num, protos);
> >  			ipc = ipc->next;
> >  		}
> > -		if ((r = set_arg(argp, protos, 8 * sizeof(long))))
> > +		if ((r = set_arg(argp, protos, sizeof(protos))))
> 
> This changes the bit endianess.

How does it do that?

include/linux/bitops.h:#define BIT_MASK(nr)		(1UL << ((nr) % BITS_PER_LONG))
include/linux/bitops.h:#define BIT_WORD(nr)		((nr) / BITS_PER_LONG)

include/asm-generic/bitops/atomic.h:static inline void set_bit(int nr, volatile unsigned long *addr)
include/asm-generic/bitops/atomic.h-{
include/asm-generic/bitops/atomic.h-	unsigned long mask = BIT_MASK(nr);
include/asm-generic/bitops/atomic.h-	unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
include/asm-generic/bitops/atomic.h-	unsigned long flags;
include/asm-generic/bitops/atomic.h-
include/asm-generic/bitops/atomic.h-	_atomic_spin_lock_irqsave(p, flags);
include/asm-generic/bitops/atomic.h-	*p  |= mask;
include/asm-generic/bitops/atomic.h-	_atomic_spin_unlock_irqrestore(p, flags);
include/asm-generic/bitops/atomic.h-}


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