[PATCH 2/3] kexec: ensure user memory sizes do not wrap

[Minfei Huang]

On 04/28/16 at 01:22pm, Russell King - ARM Linux wrote:
> On Thu, Apr 28, 2016 at 07:07:22PM +0800, Minfei Huang wrote:
> > On 04/14/16 at 09:00pm, Russell King wrote:
> > > Ensure that user memory sizes do not wrap around when validating the
> > > user input, which can lead to the following input validation working
> > > incorrectly.
> > > 
> > > Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
> > > ---
> > >  kernel/kexec_core.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> > > index 8d34308ea449..d719a4d0ef55 100644
> > > --- a/kernel/kexec_core.c
> > > +++ b/kernel/kexec_core.c
> > > @@ -169,6 +169,8 @@ int sanity_check_segment_list(struct kimage *image)
> > >  
> > >  		mstart = image->segment[i].mem;
> > >  		mend   = mstart + image->segment[i].memsz;
> > > +		if (mstart > mend)
> > > +			return result;
> > 
> > The type of image->segment[i].memsz is unsigned. So it is no need to
> > have a test here.
> 
> Absolutely wrong.  Consider the case:
> 
> 	segment[i].mem = 0xfff00000;
> 	segment[i].size = 0x00200000;
> 
> Here, mstart will be 0xfff00000, and mend will be 0x00100000.  Just
> because it's some random type does not make things magically work.

Hi, Russell.

Do you mean in PAE mode? If so, we will be in big trouble, because there
are a lot of functions which use unsigned long to store memory address,
and this type is 32 bit in PAE mode.

Thanks
Minfei