Re: [PATCH] libxc: Have xc_translate_foreign_address() set errno properly

[Wei Liu <wei.liu2@citrix.com>]

On Thu, Mar 03, 2016 at 02:53:25PM +0200, Razvan Cojocaru wrote:
> On 03/03/2016 02:47 PM, Wei Liu wrote:
> > On Wed, Mar 02, 2016 at 08:51:51AM +0200, Razvan Cojocaru wrote:
> >> Currently it's possible for xc_translate_foreign_address() to fail
> >> and errno still be set to success. This patch fixes the issue.
> >> Based on the first half of Don Slutz' patch:
> >> http://lists.xen.org/archives/html/xen-devel/2014-03/msg03720.html
> >>
> >> Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
> >> ---
> >>  tools/libxc/xc_pagetab.c | 36 +++++++++++++++++++++++++++++++++---
> >>  1 file changed, 33 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/tools/libxc/xc_pagetab.c b/tools/libxc/xc_pagetab.c
> >> index ec97890..f7dc30b 100644
> >> --- a/tools/libxc/xc_pagetab.c
> >> +++ b/tools/libxc/xc_pagetab.c
> >> @@ -34,9 +34,14 @@ unsigned long xc_translate_foreign_address(xc_interface *xch, uint32_t dom,
> >>      int size, level, pt_levels = 2;
> >>      void *map;
> >>  
> >> -    if (xc_domain_getinfo(xch, dom, 1, &dominfo) != 1 
> >> +    if (xc_domain_getinfo(xch, dom, 1, &dominfo) != 1
> >>          || dominfo.domid != dom)
> >> +    {
> >> +        if (errno == 0)
> >> +            errno = EINVAL;
> >> +
> >>          return 0;
> >> +    }
> >>  
> > 
> > Shouldn't we look into fixing the libxc functions that fail to set errno?
> > 
> > With an approach like this you end up getting whatever errno set prior
> > to calling xc_ function, which isn't very helpful in any case.
> 
> Yes, you're right. I took that part of Don's patch a while ago and ran
> with it, but a better approach would be indeed to make sure that all
> those functions do set errno properly - so I'll check to see if they do.
> 
> The only exception is the "if (!(pte & 1))" case, where errno should
> just be set directly I think.
> 
> I'll see if I can spin this into a V2.
> 

Thanks!

> 
> Thanks,
> Razvan

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