Re: [PATCH v2 0/2] acpi/nfit: Fix command-supported detection

[Dan Williams]

On Tue, Jan 15, 2019 at 12:39 PM Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
>
> Dan Williams <dan.j.williams@xxxxxxxxx> writes:
>
> > On Tue, Jan 15, 2019 at 6:16 AM Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
> >>
> >> Dan Williams <dan.j.williams@xxxxxxxxx> writes:
> >>
> >> > Changes since v1 [1]:
> >> > * Include another patch make sure that function-number zero can be
> >> >   safely used as an invalid function number (Jeff)
> >> > * Add a comment clarifying why zero is an invalid function number (Jeff)
> >> > * Pass nfit_mem to cmd_to_func() (Jeff)
> >> > * Collect a Tested-by from Sujith
> >> > [1]: https://lists.01.org/pipermail/linux-nvdimm/2019-January/019435.html
> >>
> >> For the series:
> >>
> >> Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
> >>
> >> Thanks, Dan!
> >
> > Thanks, although I just realized one more change. The ND_CMD_CALL case
> > should zero out command after the function translation, otherwise
> > userspace can call functions that the kernel is blocking in the
> > dsm_mask.
> >
> > Holler if this invalidates your "Reviewed-by".
>
> AAAAAAAHHHHHHHHHH!!!!
>
> :)
>
> > diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
> > index 87e02f281e51..d7747aceb7ab 100644
> > --- a/drivers/acpi/nfit/core.c
> > +++ b/drivers/acpi/nfit/core.c
> > @@ -463,6 +463,12 @@ int acpi_nfit_ctl(struct nvdimm_bus_descriptor
> > *nd_desc, struct nvdimm *nvdimm,
> >                 func = cmd_to_func(nfit_mem, cmd, buf);
> >                 if (func < 0)
> >                         return func;
> > +               /*
> > +                * In the ND_CMD_CALL case we're now dependent on 'func'
> > +                * being validated by the dimm's dsm_mask
> > +                */
> > +               if (cmd == ND_CMD_CALL)
> > +                       cmd = 0;
> >                 dimm_name = nvdimm_name(nvdimm);
> >                 cmd_name = nvdimm_cmd_name(cmd);
> >                 cmd_mask = nvdimm_cmd_mask(nvdimm);
>                 dsm_mask = nfit_mem->dsm_mask;
>                 desc = nd_cmd_dimm_desc(cmd);
>
> That sure doesn't look right.  Now cmd_name and desc will be wrong.

Ah, whoops, yes good catch. Guess this shows there is not good
ND_CMD_CALL coverage in the unit tests...

>
> > @@ -477,8 +483,10 @@ int acpi_nfit_ctl(struct nvdimm_bus_descriptor
> > *nd_desc, struct nvdimm *nvdimm,
> >                 cmd_name = nvdimm_bus_cmd_name(cmd);
> >                 cmd_mask = nd_desc->cmd_mask;
> >                 dsm_mask = cmd_mask;
> > -               if (cmd == ND_CMD_CALL)
> > +               if (cmd == ND_CMD_CALL) {
> >                         dsm_mask = nd_desc->bus_dsm_mask;
> > +                       cmd = 0;
> > +               }
> >                 desc = nd_cmd_bus_desc(cmd);
>
> And again here.
>
> We could reorder the zeroing, or you could modify the check for a valid
> comand/function.  Something like this?
>
>         /*
>          * Check for a valid command.  For ND_CMD_CALL, we also
>          * have to make sure that the DSM function is supported.
>          */
>         if (cmd == ND_CMD_CALL && !test_bit(func, &dsm_mask))
>                 return -ENOTTY;
>         else if (!test_bit(cmd, &cmd_mask))
>                 return -ENOTTY;
>
> Which way do you think is cleaner?

Modifying the check looks cleaner. Thanks for hollering!