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

[Robert Richter]

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@xxxxxxx>
---
 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;
-- 
2.39.5