[ROOT]Gaining write access on system partition

The latest update to .368 restricts access to /system, in particular 'mount -o remount,rw /system' won't give write access.

With the SuperSU 'supolicy' tool and a current busybox there is an easy way around the protection:

Code:

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/system/xbin/supolicy --live \
  "allow init_shell unlabeled file {execute execute_no_trans}"\
  "allow  {init_shell kernel} {device unlabeled mmc_block_device} blk_file {getattr read write open ioctl}"\
  "allow init_shell kernel process setsched"\
  "allow init_shell {rootfs labeledfs} filesystem {mount umount remount}"

mknod /dev/loop2 b 7 2
losetup /dev/loop2 /dev/block/mmcblk0 -o 96468992
mount -t ext4 /dev/loop2 /system

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The number in the losetup command is the position of the system partition in bytes in the internal memory. (This number in blocks (bytes = blocks * 512) is displayed in the expert mode of fdisk)

This works because we do not use the device corresponding to the system partition but construct an equivalent device.