pds_fwctl: Replace kzalloc + copy_from_user with memdup_user in pdsfc_fw_rpc

Replace kzalloc() followed by copy_from_user() with memdup_user() to
improve and simplify pdsfc_fw_rpc().

Return early if an error occurs and remove the obsolete 'err_out' label.

No functional changes intended.

Link: https://patch.msgid.link/r/[e-mail]
Signed-off-by: Thorsten Blum <[e-mail]>
Reviewed-by: Dave Jiang <[e-mail]>
Reviewed-by: Jason Gunthorpe <[e-mail]>
Tested-by: Brett Creeley <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

drivers/fwctl/pds/main.c

···
 #include <linux/pci.h>
 #include <linux/vmalloc.h>
 #include <linux/bitfield.h>
+#include <linux/string.h>
 
 #include <uapi/fwctl/fwctl.h>
 #include <uapi/fwctl/pds.h>
···
 		return ERR_PTR(err);
 
 	if (rpc->in.len > 0) {
-		in_payload = kzalloc(rpc->in.len, GFP_KERNEL);
-		if (!in_payload) {
-			dev_err(dev, "Failed to allocate in_payload\n");
-			err = -ENOMEM;
-			goto err_out;
-		}
-
-		if (copy_from_user(in_payload, u64_to_user_ptr(rpc->in.payload),
-				   rpc->in.len)) {
+		in_payload = memdup_user(u64_to_user_ptr(rpc->in.payload), rpc->in.len);
+		if (IS_ERR(in_payload)) {
 			dev_dbg(dev, "Failed to copy in_payload from user\n");
-			err = -EFAULT;
-			goto err_in_payload;
+			return in_payload;
 		}
 
 		in_payload_dma_addr = dma_map_single(dev->parent, in_payload,
···
 				 rpc->in.len, DMA_TO_DEVICE);
 err_in_payload:
 	kfree(in_payload);
-err_out:
 	if (err)
 		return ERR_PTR(err);