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.

---------

- Remove duplicate checks

Signed-off-by: backslashxx <118538522+backslashxx@users.noreply.github.com>
Co-authored-by: weishu <twsxtd@gmail.com>
Co-authored-by: ShirkNeko <109797057+ShirkNeko@users.noreply.github.com>

kernel/umount_manager.h

@@ -16,7 +16,6 @@ enum umount_entry_state {
 struct umount_entry {
     struct list_head list;
     char path[256];
-    bool check_mnt;
     int flags;
     enum umount_entry_state state;
     bool is_default;
@@ -40,7 +39,6 @@ enum umount_manager_op {
 struct ksu_umount_manager_cmd {
     __u32 operation;
     char path[256];
-    __u8 check_mnt;
     __s32 flags;
     __u32 count;
     __aligned_u64 entries_ptr;
@@ -48,7 +46,6 @@ struct ksu_umount_manager_cmd {
 
 struct ksu_umount_entry_info {
     char path[256];
-    __u8 check_mnt;
     __s32 flags;
     __u8 is_default;
     __u32 state;
@@ -57,7 +54,7 @@ struct ksu_umount_entry_info {
 
 int ksu_umount_manager_init(void);
 void ksu_umount_manager_exit(void);
-int ksu_umount_manager_add(const char *path, bool check_mnt, int flags, bool is_default);
+int ksu_umount_manager_add(const char *path, int flags, bool is_default);
 int ksu_umount_manager_remove(const char *path);
 void ksu_umount_manager_execute_all(const struct cred *cred);
 int ksu_umount_manager_get_entries(struct ksu_umount_entry_info __user *entries, u32 *count);