Re: [PATCH] ACPI: NFIT: Fix input validation of bus-family

[Jeff Moyer <jmoyer@redhat.com>]

Dan Williams <dan.j.williams@intel.com> writes:

> Dan reports that smatch thinks userspace can craft an out-of-bound bus
> family number. However, nd_cmd_clear_to_send() blocks all non-zero
> values of bus-family since only the kernel can initiate these commands.
> However, in the speculation path, family is a user controlled array
> index value so mask it for speculation safety. Also, since the
> nd_cmd_clear_to_send() safety is non-obvious and possibly may change in
> the future include input validation is if userspace could get past the
> nd_cmd_clear_to_send() gatekeeper.
>
> Link: http://lore.kernel.org/r/20201111113000.GA1237157@mwanda
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Fixes: 6450ddbd5d8e ("ACPI: NFIT: Define runtime firmware activation commands")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/acpi/nfit/core.c |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
> index cda7b6c52504..b11b08a60684 100644
> --- a/drivers/acpi/nfit/core.c
> +++ b/drivers/acpi/nfit/core.c
> @@ -5,6 +5,7 @@
>  #include <linux/list_sort.h>
>  #include <linux/libnvdimm.h>
>  #include <linux/module.h>
> +#include <linux/nospec.h>
>  #include <linux/mutex.h>
>  #include <linux/ndctl.h>
>  #include <linux/sysfs.h>
> @@ -479,8 +480,11 @@ int acpi_nfit_ctl(struct nvdimm_bus_descriptor *nd_desc, struct nvdimm *nvdimm,
>  		cmd_mask = nd_desc->cmd_mask;
>  		if (cmd == ND_CMD_CALL && call_pkg->nd_family) {
>  			family = call_pkg->nd_family;
> -			if (!test_bit(family, &nd_desc->bus_family_mask))
> +			if (family > NVDIMM_BUS_FAMILY_MAX ||
> +			    !test_bit(family, &nd_desc->bus_family_mask))
>  				return -EINVAL;
> +			family = array_index_nospec(family,
> +						    NVDIMM_BUS_FAMILY_MAX + 1);
>  			dsm_mask = acpi_desc->family_dsm_mask[family];
>  			guid = to_nfit_bus_uuid(family);
>  		} else {

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>