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

[Suraj Sonawane <surajsonawane0215@gmail.com>]

On 13/11/24 10:08, Alison Schofield wrote:
> 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
>>
>>
Thank you for the feedback and your time.

I appreciate your review and coding convention insights. I have studied 
the suggested change and updated the patch.

I will test the updated patch with syzbot and submit a new version very 
shortly.

Best regards,
Suraj Sonawane