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

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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>
This commit is contained in:
backslashxx
2025-11-18 11:10:44 +08:00
committed by ShirkNeko
parent 2aa0034695
commit 3510203fa6
4 changed files with 156 additions and 40 deletions
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59
kernel/kernel_umount.c
View File

@@ -44,28 +44,11 @@ static const struct ksu_feature_handler kernel_umount_handler = {
.set_handler = kernel_umount_feature_set,
};
static bool should_umount(struct path *path)
{
if (!path) {
return false;
}
if (current->nsproxy->mnt_ns == init_nsproxy.mnt_ns) {
pr_info("ignore global mnt namespace process: %d\n",
current_uid().val);
return false;
}
if (path->mnt && path->mnt->mnt_sb && path->mnt->mnt_sb->s_type) {
const char *fstype = path->mnt->mnt_sb->s_type->name;
return strcmp(fstype, "overlay") == 0;
}
return false;
}
#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 9, 0) || defined(KSU_HAS_PATH_UMOUNT)
#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 9, 0) || \
defined(KSU_HAS_PATH_UMOUNT)
extern int path_umount(struct path *path, int flags);
static void ksu_umount_mnt(const char *__never_use_mnt, struct path *path, int flags)
static void ksu_umount_mnt(const char *__never_use_mnt, struct path *path,
int flags)
{
int err = path_umount(path, flags);
if (err) {
@@ -91,12 +74,12 @@ static void ksu_sys_umount(const char *mnt, int flags)
#define ksu_umount_mnt(mnt, __unused, flags) \
({ \
path_put(__unused); \
ksu_sys_umount(mnt, flags); \
ksu_sys_umount(mnt, flags); \
})
#endif
static void try_umount(const char *mnt, bool check_mnt, int flags)
static void try_umount(const char *mnt, int flags)
{
struct path path;
int err = kern_path(mnt, 0, &path);
@@ -110,25 +93,17 @@ static void try_umount(const char *mnt, bool check_mnt, int flags)
return;
}
// we are only interest in some specific mounts
if (check_mnt && !should_umount(&path)) {
path_put(&path);
return;
}
ksu_umount_mnt(mnt, &path, flags);
}
static inline void do_ksu_umount_lists(void)
static inline void do_umount_work(void)
{
// fixme: use `collect_mounts` and `iterate_mount` to iterate all mountpoint and
// filter the mountpoint whose target is `/data/adb`
try_umount("/odm", true, 0);
try_umount("/system", true, 0);
try_umount("/vendor", true, 0);
try_umount("/product", true, 0);
try_umount("/system_ext", true, 0);
try_umount("/data/adb/modules", false, MNT_DETACH);
struct mount_entry *entry;
list_for_each_entry (entry, &mount_list, list) {
pr_info("%s: unmounting: %s flags 0x%x\n", __func__,
entry->umountable, entry->flags);
try_umount(entry->umountable, entry->flags);
}
}
#ifdef KSU_SHOULD_USE_NEW_TP
@@ -145,7 +120,9 @@ static void umount_tw_func(struct callback_head *cb)
saved = override_creds(tw->old_cred);
}
do_ksu_umount_lists();
down_read(&mount_list_lock);
do_umount_work();
up_read(&mount_list_lock);
if (saved)
revert_creds(saved);
@@ -208,7 +185,9 @@ int ksu_handle_umount(uid_t old_uid, uid_t new_uid)
}
#else
// Using task work for non-kp context is expansive?
do_ksu_umount_lists();
down_read(&mount_list_lock);
do_umount_work();
up_read(&mount_list_lock);
#endif
return 0;