Re: [PATCH v2] acpi: nfit: vmalloc-out-of-bounds Read in acpi_nfit_ctl

[Alison Schofield]

On Tue, Nov 12, 2024 at 10:50:35AM +0530, Suraj Sonawane wrote:
> Fix an issue detected by syzbot with KASAN:
> 
> BUG: KASAN: vmalloc-out-of-bounds in cmd_to_func drivers/acpi/nfit/
> core.c:416 [inline]
> BUG: KASAN: vmalloc-out-of-bounds in acpi_nfit_ctl+0x20e8/0x24a0
> drivers/acpi/nfit/core.c:459
> 
> The issue occurs in `cmd_to_func` when the `call_pkg->nd_reserved2`
> array is accessed without verifying that `call_pkg` points to a
> buffer that is sized appropriately as a `struct nd_cmd_pkg`. This
> could lead to out-of-bounds access and undefined behavior if the
> buffer does not have sufficient space.
> 
> To address this issue, a check was added in `acpi_nfit_ctl()` to
> ensure that `buf` is not `NULL` and `buf_len` is greater than or
> equal to `sizeof(struct nd_cmd_pkg)` before casting `buf` to
> `struct nd_cmd_pkg *`. This ensures safe access to the members of
> `call_pkg`, including the `nd_reserved2` array.

That all sounds good! A couple of coding conventions fixups suggested
below -

snip

> @@ -439,7 +439,7 @@ int acpi_nfit_ctl(struct nvdimm_bus_descriptor *nd_desc, struct nvdimm *nvdimm,
>  {
>  	struct acpi_nfit_desc *acpi_desc = to_acpi_desc(nd_desc);
>  	struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
> -	union acpi_object in_obj, in_buf, *out_obj;
> +	union acpi_object in_obj, in_buf, *out_obj = NULL;
>  	const struct nd_cmd_desc *desc = NULL;
>  	struct device *dev = acpi_desc->dev;
>  	struct nd_cmd_pkg *call_pkg = NULL;
> @@ -454,8 +454,14 @@ int acpi_nfit_ctl(struct nvdimm_bus_descriptor *nd_desc, struct nvdimm *nvdimm,
>  	if (cmd_rc)
>  		*cmd_rc = -EINVAL;
>  
> -	if (cmd == ND_CMD_CALL)
> -		call_pkg = buf;
> +	if (cmd == ND_CMD_CALL) {
> +		if (buf == NULL || buf_len < sizeof(struct nd_cmd_pkg)) {

Comparison to NULL and sizeof() usage preferred like this:
	if (!buf || buf_len < sizeof(*call_pkg))


-snip
> 
>