efi/efi_test: Use memdup_user() helper

Use memdup_user() helper instead of open-coding to simplify the code.
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Ivan Hu <ivan.hu@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170602135207.21708-12-ard.biesheuvel@linaro.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

drivers/firmware/efi/test/efi_test.c

@@ -71,18 +71,13 @@ copy_ucs2_from_user_len(efi_char16_t **dst, efi_char16_t __user *src,
 	if (!access_ok(VERIFY_READ, src, 1))
 		return -EFAULT;
 
-	buf = kmalloc(len, GFP_KERNEL);
-	if (!buf) {
+	buf = memdup_user(src, len);
+	if (IS_ERR(buf)) {
 		*dst = NULL;
-		return -ENOMEM;
+		return PTR_ERR(buf);
 	}
 	*dst = buf;
 
-	if (copy_from_user(*dst, src, len)) {
-		kfree(buf);
-		return -EFAULT;
-	}
-
 	return 0;
 }