Re: [PATCH v2] libnvdimm/labels: Fix divide error in nd_label_data_init()

[Davidlohr Bueso]

On Thu, 20 Mar 2025, Robert Richter wrote:

> If a faulty 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);
>
> 4) A subsequent DIV_ROUND_UP() causes a division by zero:
>
> drivers/nvdimm/label.c: /* Make our initial read size a multiple of max_xfer size */
> drivers/nvdimm/label.c: read_size = min(DIV_ROUND_UP(read_size, max_xfer) * max_xfer,
> drivers/nvdimm/label.c-                 config_size);
>
> Fix this by checking the config size parameter by extending an
> existing check.
>
> Signed-off-by: Robert Richter <rrichter@xxxxxxx>
> Reviewed-by: Pankaj Gupta <pankaj.gupta@xxxxxxx>
> Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>

Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>