nvme: sanitize metadata bounce buffer for reads

User can request more metadata bytes than the device will write. Ensure
kernel buffer is initialized so we're not leaking unsanitized memory on
the copy-out.

Fixes: 0b7f1f2 ("nvme: use the block layer for userspace passthrough metadata")
Reviewed-by: Jens Axboe <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Kanchan Joshi <[email protected]>
Reviewed-by: Chaitanya Kulkarni <[email protected]>
Signed-off-by: Keith Busch <[email protected]>

Author: keithbusch

drivers/nvme/host/ioctl.c

@@ -108,9 +108,13 @@ static void *nvme_add_user_metadata(struct request *req, void __user *ubuf,
 	if (!buf)
 		goto out;
 
-	ret = -EFAULT;
-	if ((req_op(req) == REQ_OP_DRV_OUT) && copy_from_user(buf, ubuf, len))
-		goto out_free_meta;
+	if (req_op(req) == REQ_OP_DRV_OUT) {
+		ret = -EFAULT;
+		if (copy_from_user(buf, ubuf, len))
+			goto out_free_meta;
+	} else {
+		memset(buf, 0, len);
+	}
 
 	bip = bio_integrity_alloc(bio, GFP_KERNEL, 1);
 	if (IS_ERR(bip)) {