diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index 7d4e7b9..a0f54e8 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -568,13 +568,18 @@
 {
 	struct mtd_write_req req;
 	struct mtd_oob_ops ops;
-	void __user *usr_data, *usr_oob;
+	const void __user *usr_data, *usr_oob;
 	int ret;
 
-	if (copy_from_user(&req, argp, sizeof(req)) ||
-			!access_ok(VERIFY_READ, req.usr_data, req.len) ||
-			!access_ok(VERIFY_READ, req.usr_oob, req.ooblen))
+	if (copy_from_user(&req, argp, sizeof(req)))
 		return -EFAULT;
+
+	usr_data = (const void __user *)(uintptr_t)req.usr_data;
+	usr_oob = (const void __user *)(uintptr_t)req.usr_oob;
+	if (!access_ok(VERIFY_READ, usr_data, req.len) ||
+	    !access_ok(VERIFY_READ, usr_oob, req.ooblen))
+		return -EFAULT;
+
 	if (!mtd->_write_oob)
 		return -EOPNOTSUPP;
 
@@ -583,10 +588,7 @@
 	ops.ooblen = (size_t)req.ooblen;
 	ops.ooboffs = 0;
 
-	usr_data = (void __user *)(uintptr_t)req.usr_data;
-	usr_oob = (void __user *)(uintptr_t)req.usr_oob;
-
-	if (req.usr_data) {
+	if (usr_data) {
 		ops.datbuf = memdup_user(usr_data, ops.len);
 		if (IS_ERR(ops.datbuf))
 			return PTR_ERR(ops.datbuf);
@@ -594,7 +596,7 @@
 		ops.datbuf = NULL;
 	}
 
-	if (req.usr_oob) {
+	if (usr_oob) {
 		ops.oobbuf = memdup_user(usr_oob, ops.ooblen);
 		if (IS_ERR(ops.oobbuf)) {
 			kfree(ops.datbuf);