We used to construct /sbin tmpfs overlay in early-init stage after
SELinux is properly initialized. However the way it is implemented
(forking daemon from magiskinit with complicated file waiting triggers)
is extremely complicated and error prone.
This commit moves the construction of the sbin overlay to pre-init
stage. The catch is that since SELinux is not present at that point,
proper selabel has to be reconstructed afterwards. Some additional
SEPolicy rules are added to make sure init can access magisk binaries,
and the secontext relabeling task is assigned to the main Magisk daemon.
Android Q init assumes rootfs to always be on EXT4 images, thus
never runs restorecon on the whole root directory. This is an issue
because some folders in rootfs were set with special selabels in
the system partition, but when copying over to initramfs by magiskinit,
these labels will not be preserved.
So the solution is to relabel the files in rootfs with the original
context right? Yes, but rootfs does not allow security xattr to be set
on files before the kernel SELinux initializes with genfs_contexts.
We have to load our sepolicy to the kernel before we clone the root
directory from system partition, which we will also restore the selabel
in the meantime.
Unfortunately this means that for each reboot, the exact same policy
will be loaded to the kernel twice: once in magiskinit so we can label
rootfs properly, and once by the original init, which is part of the
boot procedure. There is no easy way to prevent init from loading
sepolicy, as init will refuse to continue if policy loading has failed.
Since we switched to imageless Magisk, module files are directly
stored in /data. However, /data is mounted with nosuid, which also
prevents SELinux typetransition to work (auto transition from one
domain to another when executing files with specific context).
This could cause serious issues when we are replacing system critical
components (e.g. app_process for Xposed), because most of them
are daemons that run in special process domains.
This commit introduced /data mirror. Using similar mirroring technique
we used for system and vendor, we mount another mirror that mounts
/data without nosuid flag. All module files are then mounted from this
mirror mountpoint instead of directly from /data.
Close#1080
Mounting ext4 images causes tons of issues, such as unmountable with broken F2FS drivers.
Resizing is also very complicated and does not work properly on all devices.
Each step in either measuring free space, resizing, and shrinking the image is a
point of failure, and either step's failure could cause the module system completely broken.
The new method is to directly store modules into /data/adb/modules, and for module installation
on boot /data/adb/modules_update. Several compatibility layers has been done: the new path is
bind mounted to the old path (/sbin/.magisk/img), and the helper functions in util_functions.sh
will now transparently make existing modules install to the new location without any changes.
MagiskHide is also updated to unmount module files stored in this new location.
1. Introduce new applet: imgtool for better separation from the main program
2. Actually mount the image and check statvfs for free space in the image
This shall eliminate any possible module installation failure from image resizing issues.
