RDMA/hns: Fix NULL pointer derefernce in hns_roce_map_mr_sg()

ib_map_mr_sg() allows ULPs to specify NULL as the sg_offset argument.
The driver needs to check whether it is a NULL pointer before
dereferencing it.

Fixes: d387d4b ("RDMA/hns: Fix missing pagesize and alignment check in FRMR")
Signed-off-by: Junxian Huang <huangjunxian6@hisilicon.com>
Link: https://patch.msgid.link/20241108075743.2652258-3-huangjunxian6@hisilicon.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>

Author: Junxian Huang

drivers/infiniband/hw/hns/hns_roce_mr.c

@@ -435,15 +435,16 @@ static int hns_roce_set_page(struct ib_mr *ibmr, u64 addr)
 }
 
 int hns_roce_map_mr_sg(struct ib_mr *ibmr, struct scatterlist *sg, int sg_nents,
-		       unsigned int *sg_offset)
+		       unsigned int *sg_offset_p)
 {
+	unsigned int sg_offset = sg_offset_p ? *sg_offset_p : 0;
 	struct hns_roce_dev *hr_dev = to_hr_dev(ibmr->device);
 	struct ib_device *ibdev = &hr_dev->ib_dev;
 	struct hns_roce_mr *mr = to_hr_mr(ibmr);
 	struct hns_roce_mtr *mtr = &mr->pbl_mtr;
 	int ret, sg_num = 0;
 
-	if (!IS_ALIGNED(*sg_offset, HNS_ROCE_FRMR_ALIGN_SIZE) ||
+	if (!IS_ALIGNED(sg_offset, HNS_ROCE_FRMR_ALIGN_SIZE) ||
 	    ibmr->page_size < HNS_HW_PAGE_SIZE ||
 	    ibmr->page_size > HNS_HW_MAX_PAGE_SIZE)
 		return sg_num;
@@ -454,7 +455,7 @@ int hns_roce_map_mr_sg(struct ib_mr *ibmr, struct scatterlist *sg, int sg_nents,
 	if (!mr->page_list)
 		return sg_num;
 
-	sg_num = ib_sg_to_pages(ibmr, sg, sg_nents, sg_offset, hns_roce_set_page);
+	sg_num = ib_sg_to_pages(ibmr, sg, sg_nents, sg_offset_p, hns_roce_set_page);
 	if (sg_num < 1) {
 		ibdev_err(ibdev, "failed to store sg pages %u %u, cnt = %d.\n",
 			  mr->npages, mr->pbl_mtr.hem_cfg.buf_pg_count, sg_num);