Re: [PATCH] libnvdimm/labels: Fix divide error in nd_label_data_init()

["Gupta, Pankaj" <pankaj.gupta@amd.com>]

On 3/19/2025 12:32 PM, Robert Richter wrote:
> If a CXL memory device returns a broken zero LSA size in its memory
> device information (Identify Memory Device (Opcode 4000h), CXL
> spec. 3.1, 8.2.9.9.1.1), a divide error occurs in the libnvdimm
> driver:
> 
>   Oops: divide error: 0000 [#1] PREEMPT SMP NOPTI
>   RIP: 0010:nd_label_data_init+0x10e/0x800 [libnvdimm]
> 
> Code and flow:
> 
> 1) CXL Command 4000h returns LSA size = 0,
> 2) config_size is assigned to zero LSA size (CXL pmem driver):
> 
> drivers/cxl/pmem.c:             .config_size = mds->lsa_size,
> 
> 3) max_xfer is set to zero (nvdimm driver):
> 
> drivers/nvdimm/label.c: max_xfer = min_t(size_t, ndd->nsarea.max_xfer, config_size);
> drivers/nvdimm/label.c: if (read_size < max_xfer) {
> drivers/nvdimm/label.c-         /* trim waste */
> 
> 4) DIV_ROUND_UP() causes division by zero:
> 
> drivers/nvdimm/label.c:         max_xfer -= ((max_xfer - 1) - (config_size - 1) % max_xfer) /
> drivers/nvdimm/label.c:                     DIV_ROUND_UP(config_size, max_xfer);
> drivers/nvdimm/label.c-         /* make certain we read indexes in exactly 1 read */
> drivers/nvdimm/label.c:         if (max_xfer < read_size)
> drivers/nvdimm/label.c:                 max_xfer = read_size;
> drivers/nvdimm/label.c- }
> 
> Fix this by checking the config size parameter by extending an
> existing check.
> 
> Signed-off-by: Robert Richter <rrichter@amd.com>

LGTM

Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>

> ---
>   drivers/nvdimm/label.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/nvdimm/label.c b/drivers/nvdimm/label.c
> index 082253a3a956..04f4a049599a 100644
> --- a/drivers/nvdimm/label.c
> +++ b/drivers/nvdimm/label.c
> @@ -442,7 +442,8 @@ int nd_label_data_init(struct nvdimm_drvdata *ndd)
>   	if (ndd->data)
>   		return 0;
>   
> -	if (ndd->nsarea.status || ndd->nsarea.max_xfer == 0) {
> +	if (ndd->nsarea.status || ndd->nsarea.max_xfer == 0 ||
> +	    ndd->nsarea.config_size == 0) {
>   		dev_dbg(ndd->dev, "failed to init config data area: (%u:%u)\n",
>   			ndd->nsarea.max_xfer, ndd->nsarea.config_size);
>   		return -ENXIO;