Subject: Re: [PATCH 3/3] powerpc/fsl: add MPIC timer wakeup support

From: Scott Wood <[email-masked]>
Date: Wed, 27 Mar 2013 15:25:59 -0500

On 03/26/2013 10:21:04 PM, Wang Dongsheng-B40534 wrote:
>=20
>=20
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Wednesday, March 27, 2013 1:36 AM
> > To: Wang Dongsheng-B40534
> > Cc: Wood Scott-B07421; Gala Kumar-B11780; =20
> [email-masked];
> > Zhao Chenhui-B35336; Li Yang-R58472
> > Subject: Re: [PATCH 3/3] powerpc/fsl: add MPIC timer wakeup support
> >
> > On 03/25/2013 10:27:24 PM, Wang Dongsheng-B40534 wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Wood Scott-B07421
> > > > Sent: Saturday, March 23, 2013 6:11 AM
> > > > To: Wang Dongsheng-B40534
> > > > Cc: Wood Scott-B07421; Gala Kumar-B11780;
> > > [email-masked];
> > > > Zhao Chenhui-B35336; Li Yang-R58472
> > > > Subject: Re: [PATCH 3/3] powerpc/fsl: add MPIC timer wakeup =20
> support
> > > >
> > > > On 03/22/2013 12:46:24 AM, Wang Dongsheng-B40534 wrote:
> > > > > Under what case is unsafe, please make sense.
> > > >
> > > > char buffer[1] =3D { '5' };
> > > > write(fd, &buffer, 1);
> > > >
> > > > What comes after that '5' byte in the pointer you pass to =20
> kstrtol?
> > > >
> > > The buffer is userspace. It will fall in the kernel space.
> > > Kernel will get a free page, and copy the buffer to page.
> > > This page has been cleared before copy to page.
> > > The page has already have null-terminated.
> >
> > It doesn't allocate a whole page, it uses kmalloc (not kzalloc!).  =20
> Even
> > if kzalloc were used, a larger user buffer could be the exact size =20
> of the
> > region that was allocated.
> >
> > See memdup_user() in mm/util.c
> >
> Did you miss something?
> See fill_write_buffer() in fs/sysfs/file.c. It's used =20
> get_zeroed_page()...

OK, I was looking at fs/sysfs/bin.c which is something slightly =20
different.

fill_write_buffer() forces the size to be no more than "PAGE_SIZE - 1" =20
so we know there's a terminator.

Perhaps kernel/rtmutex-tester.c and kernel/time/clocksource.c are =20
similarly confused?

-Scott=