Re: [PATCH v3 4/5] drm: Add decoding of i915 ioctls

Gabriel Laskar
2015-07-06T14:40:26Z

On Mon, 6 Jul 2015 12:35:52 +0200
Patrik Jakobsson <patrik.jakobsson@linux.intel.com> wrote:

> On Fri, Jul 03, 2015 at 03:36:09AM +0300, Dmitry V. Levin wrote:
> > On Wed, Jul 01, 2015 at 02:52:47PM +0200, Patrik Jakobsson wrote:
> > [...]
> > > --- a/drm.c
> > > +++ b/drm.c
> > > @@ -35,6 +35,9 @@
> > >
> > > #define DRM_MAX_NAME_LEN 128
> > >
> > > +extern int drm_i915_decode_number(struct tcb *tcp, unsigned int arg);
> >
> > Please rename "arg" to "code", and ...
> >
> > > +extern int drm_i915_ioctl(struct tcb *tcp, const unsigned int code, long arg);
> >
> > ... move both declarations to defs.h to make them visible also
> > in the file where these functions are defined.
> >
> > [...]
> > > +static int i915_setparam(struct tcb *tcp, const unsigned int code, long arg)
> > > +{
> > > + struct drm_i915_setparam param;
> > > +
> > > + if (entering(tcp)) {
> > > + if (umove(tcp, arg, &param))
> > > + return 0;
> > > +
> > > + tprints(", {param=");
> > > + printxval(drm_i915_setparams, param.param, "I915_PARAM_???");
> > > + tprintf(", value=%d}", param.value);
> > > + }
> > > +
> > > + return 1;
> > > +}
> >
> > In this and most of other parsers of _IOC_WRITE ioctls added by this and
> > the next patches, any error in parser that leads to "return 0" will result
> > to disabled "arg" decoding, including the fallback decoding performed by
> > sys_ioctl.
> >
> > Maybe it's time to deal with this issue in a more generic way.
> >
>
> Yes, I'm thinking SYS_FUNC(ioctl) could be improved. But on the other hand how
> likely is it that we fail in umove and what chance do we have to recover from
> that anyway? All I can think of is OOM.

umove() can fail in multiple ways. For example, if the memory is not
valid in the tracee, umove() will fail.

Anyway, SYS_FUNC(ioctl) is a bit complicated, and the handling of the
fallbacks on failure should be more generic.

--
Gabriel Laskar