ksmbd: check invalid FileOffset and BeyondFinalZero in FSCTL_ZERO_DATA

FileOffset should not be greater than BeyondFinalZero in FSCTL_ZERO_DATA.
And don't call ksmbd_vfs_zero_data() if length is zero.

Cc: stable@vger.kernel.org
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/smb2pdu.c

@@ -7700,7 +7700,7 @@ int smb2_ioctl(struct ksmbd_work *work)
 	{
 		struct file_zero_data_information *zero_data;
 		struct ksmbd_file *fp;
-		loff_t off, len;
+		loff_t off, len, bfz;
 
 		if (!test_tree_conn_flag(work->tcon, KSMBD_TREE_CONN_FLAG_WRITABLE)) {
 			ksmbd_debug(SMB,
@@ -7717,19 +7717,26 @@ int smb2_ioctl(struct ksmbd_work *work)
 		zero_data =
 			(struct file_zero_data_information *)&req->Buffer[0];
 
-		fp = ksmbd_lookup_fd_fast(work, id);
-		if (!fp) {
-			ret = -ENOENT;
+		off = le64_to_cpu(zero_data->FileOffset);
+		bfz = le64_to_cpu(zero_data->BeyondFinalZero);
+		if (off > bfz) {
+			ret = -EINVAL;
 			goto out;
 		}
 
-		off = le64_to_cpu(zero_data->FileOffset);
-		len = le64_to_cpu(zero_data->BeyondFinalZero) - off;
+		len = bfz - off;
+		if (len) {
+			fp = ksmbd_lookup_fd_fast(work, id);
+			if (!fp) {
+				ret = -ENOENT;
+				goto out;
+			}
 
-		ret = ksmbd_vfs_zero_data(work, fp, off, len);
-		ksmbd_fd_put(work, fp);
-		if (ret < 0)
-			goto out;
+			ret = ksmbd_vfs_zero_data(work, fp, off, len);
+			ksmbd_fd_put(work, fp);
+			if (ret < 0)
+				goto out;
+		}
 		break;
 	}
 	case FSCTL_QUERY_ALLOCATED_RANGES: