kernel: expose umount list to ioctl interface (#2950)

This idea is borrowed from simonpunk's susfs4ksu.
What we see here is that, yeah well, lets just have userspace send us
what it
wants unmounted, this is better than hardcoding everything.

This also solves that issue where MNT_DETACH fails, as long as we send
unmountables in proper order.

A small anti-duplicate mechanism is also added.

While in-kernel umount is a bit worse than zygisk-provider-based ones,
this can still
serve as a healthy alternative.

---------

Signed-off-by: backslashxx <118538522+backslashxx@users.noreply.github.com>
Co-authored-by: weishu <twsxtd@gmail.com>
Signed-off-by: fc5b87cf <rissu.ntk@gmail.com>

kernel/supercalls.h

@@ -121,6 +121,16 @@ struct ksu_manage_mark_cmd {
 #define KSU_MARK_UNMARK 3
 #define KSU_MARK_REFRESH 4
 
+struct ksu_add_try_umount_cmd {
+	__aligned_u64 arg; // char ptr, this is the mountpoint
+	__u32 flags; // this is the flag we use for it
+	__u8 mode; // denotes what to do with it 0:wipe_list 1:add_to_list 2:delete_entry
+};
+
+#define KSU_UMOUNT_WIPE 0 // ignore everything and wipe list
+#define KSU_UMOUNT_ADD 1 // add entry (path + flags)
+#define KSU_UMOUNT_DEL 2 // delete entry, strcmp
+
 // IOCTL command definitions
 #define KSU_IOCTL_GRANT_ROOT _IOC(_IOC_NONE, 'K', 1, 0)
 #define KSU_IOCTL_GET_INFO _IOC(_IOC_READ, 'K', 2, 0)
@@ -138,6 +148,8 @@ struct ksu_manage_mark_cmd {
 #define KSU_IOCTL_SET_FEATURE _IOC(_IOC_WRITE, 'K', 14, 0)
 #define KSU_IOCTL_GET_WRAPPER_FD _IOC(_IOC_WRITE, 'K', 15, 0)
 #define KSU_IOCTL_MANAGE_MARK _IOC(_IOC_READ | _IOC_WRITE, 'K', 16, 0)
+// #define KSU_IOCTL_NUKE_EXT4_SYSFS _IOC(_IOC_WRITE, 'K', 17, 0)
+#define KSU_IOCTL_ADD_TRY_UMOUNT _IOC(_IOC_WRITE, 'K', 18, 0)
 // Other IOCTL command definitions
 #define KSU_IOCTL_GET_FULL_VERSION _IOC(_IOC_READ, 'K', 100, 0)
 #define KSU_IOCTL_HOOK_TYPE _IOC(_IOC_READ, 'K', 101, 0)