linux-kernel - Re: [PATCH] xen: xenfs: privcmd: check put

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Date:	Fri, 29 Oct 2010 18:44:30 +0100
From:	Ian Campbell <Ian.Campbell@...citrix.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Vasiliy Kulikov <segooon@...il.com>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"virtualization@...ts.osdl.org" <virtualization@...ts.osdl.org>
Subject: Re: [PATCH] xen: xenfs: privcmd: check put_user() return code

On Fri, 2010-10-29 at 18:18 +0100, Jeremy Fitzhardinge wrote:
> On 10/28/2010 04:39 AM, Vasiliy Kulikov wrote:
> > put_user() may fail.  In this case propagate error code from
> > privcmd_ioctl_mmap_batch().
> 
> Thanks for looking at this.  I'm in two minds about this; the existing
> logic is such that these put_users can only fail if something else has
> already failed and its returning an error.  I guess it would be useful
> to get an EFAULT if you've got a problem writing back the results.
> 
> IanC, any opinion?

Not a strong one.

Perhaps what we really want in this case is for traverse_pages to return
the total number of callback failures it encountered rather than
aborting after the first failure?

On the other hand you are correct that gather_array() has already
touched all the pages which we are going to be touching here so how
likely is a new failure at this point anyway?

Ian.

> 
> Thanks,
>     J
> 
> > Signed-off-by: Vasiliy Kulikov <segooon@...il.com>
> > ---
> >  Compile tested.
> >
> >  drivers/xen/xenfs/privcmd.c |    8 ++------
> >  1 files changed, 2 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/xen/xenfs/privcmd.c b/drivers/xen/xenfs/privcmd.c
> > index f80be7f..2eb04c8 100644
> > --- a/drivers/xen/xenfs/privcmd.c
> > +++ b/drivers/xen/xenfs/privcmd.c
> > @@ -266,9 +266,7 @@ static int mmap_return_errors(void *data, void *state)
> >  	xen_pfn_t *mfnp = data;
> >  	struct mmap_batch_state *st = state;
> >  
> > -	put_user(*mfnp, st->user++);
> > -
> > -	return 0;
> > +	return put_user(*mfnp, st->user++);
> >  }
> >  
> >  static struct vm_operations_struct privcmd_vm_ops;
> > @@ -323,10 +321,8 @@ static long privcmd_ioctl_mmap_batch(void __user *udata)
> >  	up_write(&mm->mmap_sem);
> >  
> >  	if (state.err > 0) {
> > -		ret = 0;
> > -
> >  		state.user = m.arr;
> > -		traverse_pages(m.num, sizeof(xen_pfn_t),
> > +		ret = traverse_pages(m.num, sizeof(xen_pfn_t),
> >  			       &pagelist,
> >  			       mmap_return_errors, &state);
> >  	}
> 


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