Android 6 (cyanogenmod 13) external sd card write access

I always used "Samba server" application on all my android devices for uploading files, it worked great with CM12, but in CM13 even with root access Samba server can't write to external SD card, neither can "SSH server" application. As i there was some changes in android 6, but is there any way to grant write access to external SD card for some applications? I tried different samba servers, they all see external SD card and can read from there, but they just can't write. I have the same problem with Cyanogenmod 13 on two different devices, i tried to format external SD card in ext3, ext4, fat32, exfat - no difference at all. There are a lot of "SD card fix" applications in play store, but they all, as I can see for android 5, and just doesn't work for android 6. So, is it a SELinux issue? Should I add somehow user an app runs from into media_rw group? How can I do this? There is id output after ssh connection: uid=10138(u0_a138) gid=10138(u0_a138) groups=10138(u0_a138),3002(net_bt),3003(inet),9997(everybody),50138(all_a138) context=u:r:untrusted_app:s0:c512,c768 It can read but can't write on external sd card, any ideas? Thanks.