The sunxi-debug driver in Allwinner 3.4 legacy kernel for H3, A83T and H8 devices allows local users to gain root privileges by sending "rootmydevice" to /proc/sunxi_debug/sunxi_debug.
https://irclog.whitequark.org/linux-sunxi/2016-04-29#16314390
https://forum.armbian.com/index.php?/topic/1108-security-alert-for-allwinner-sun8i-h3a83th8/
http://www.securityfocus.com/bid/93442