RDMA/cxbg: Use correct sizing on buffers holding page DMA addresses

The PBL array that hold the page DMA address is sized off umem->nmap.
This can potentially cause out of bound accesses on the PBL array when
iterating the umem DMA-mapped SGL. This is because if umem pages are
combined, umem->nmap can be much lower than the number of system pages
in umem.

Use ib_umem_num_pages() to size this array.

Cc: Potnuri Bharat Teja <bharat@chelsio.com>
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/cxgb3/iwch_provider.c

@@ -539,7 +539,7 @@ static struct ib_mr *iwch_reg_user_mr(struct ib_pd *pd, u64 start, u64 length,
 
 	shift = PAGE_SHIFT;
 
-	n = mhp->umem->nmap;
+	n = ib_umem_num_pages(mhp->umem);
 
 	err = iwch_alloc_pbl(mhp, n);
 	if (err)

drivers/infiniband/hw/cxgb4/mem.c

@@ -542,7 +542,7 @@ struct ib_mr *c4iw_reg_user_mr(struct ib_pd *pd, u64 start, u64 length,
 
 	shift = PAGE_SHIFT;
 
-	n = mhp->umem->nmap;
+	n = ib_umem_num_pages(mhp->umem);
 	err = alloc_pbl(mhp, n);
 	if (err)
 		goto err_umem_release;