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

[Russell King - ARM Linux]

On Mon, Apr 18, 2016 at 01:35:34PM +0800, Baoquan He 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;
> 
> These segments are built in kexec utility, their availability should be
> guaranteed there. If without some alignment handling, wrapping around
> might not happen here. But I don't have strong objection to it.

In which case, what's the point of all the other validation which is done,
like the check below:

> >  		if ((mstart & ~PAGE_MASK) || (mend & ~PAGE_MASK))
> >  			return result;
> >  		if (mend >= KEXEC_DESTINATION_MEMORY_LIMIT)

Your reply is contradictory to the whole suite of tests which kexec does
to validate its input from userspace.

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.