SukiSU-Ultra/kernel/kernel_umount.c

#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/task_work.h>
#include <linux/cred.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/nsproxy.h>
#include <linux/path.h>
#include <linux/printk.h>
#include <linux/types.h>

#include "kernel_umount.h"
#include "klog.h" // IWYU pragma: keep
#include "allowlist.h"
#include "selinux/selinux.h"
#include "feature.h"
#include "ksud.h"

#include "umount_manager.h"
#include "sulog.h"

static bool ksu_kernel_umount_enabled = true;

static int kernel_umount_feature_get(u64 *value)
{
    *value = ksu_kernel_umount_enabled ? 1 : 0;
    return 0;
}

static int kernel_umount_feature_set(u64 value)
{
    bool enable = value != 0;
    ksu_kernel_umount_enabled = enable;
    pr_info("kernel_umount: set to %d\n", enable);
    return 0;
}

static const struct ksu_feature_handler kernel_umount_handler = {
    .feature_id = KSU_FEATURE_KERNEL_UMOUNT,
    .name = "kernel_umount",
    .get_handler = kernel_umount_feature_get,
    .set_handler = kernel_umount_feature_set,
};

extern int path_umount(struct path *path, int flags);

static void ksu_umount_mnt(struct path *path, int flags)
{
    int err = path_umount(path, flags);
    if (err) {
        pr_info("umount %s failed: %d\n", path->dentry->d_iname, err);
    }
}

void try_umount(const char *mnt, int flags)
{
    struct path path;
    int err = kern_path(mnt, 0, &path);
    if (err) {
        return;
    }

    if (path.dentry != path.mnt->mnt_root) {
        // it is not root mountpoint, maybe umounted by others already.
        path_put(&path);
        return;
    }

    ksu_umount_mnt(&path, flags);
}

struct umount_tw {
    struct callback_head cb;
    const struct cred *old_cred;
};

static void umount_tw_func(struct callback_head *cb)
{
    struct umount_tw *tw = container_of(cb, struct umount_tw, cb);
    const struct cred *saved = NULL;
    if (tw->old_cred) {
        saved = override_creds(tw->old_cred);
    }

    struct mount_entry *entry;
    down_read(&mount_list_lock);
    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);
    }
    up_read(&mount_list_lock);

    ksu_umount_manager_execute_all(tw->old_cred);

    if (saved)
        revert_creds(saved);

    if (tw->old_cred)
        put_cred(tw->old_cred);

    kfree(tw);
}

int ksu_handle_umount(uid_t old_uid, uid_t new_uid)
{
    struct umount_tw *tw;

    // if there isn't any module mounted, just ignore it!
    if (!ksu_module_mounted) {
        return 0;
    }

    if (!ksu_kernel_umount_enabled) {
        return 0;
    }

    // There are 5 scenarios:
    // 1. Normal app: zygote -> appuid
    // 2. Isolated process forked from zygote: zygote -> isolated_process
    // 3. App zygote forked from zygote: zygote -> appuid
    // 4. Isolated process froked from app zygote: appuid -> isolated_process (already handled by 3)
    // 5. Isolated process froked from webview zygote (no need to handle, app cannot run custom code)
    if (!is_appuid(new_uid) && !is_isolated_process(new_uid)) {
        return 0;
    }

    if (!ksu_uid_should_umount(new_uid) && !is_isolated_process(new_uid)) {
        return 0;
    }

    // check old process's selinux context, if it is not zygote, ignore it!
    // because some su apps may setuid to untrusted_app but they are in global mount namespace
    // when we umount for such process, that is a disaster!
    // also handle case 4 and 5
    bool is_zygote_child = is_zygote(get_current_cred());
    if (!is_zygote_child) {
        pr_info("handle umount ignore non zygote child: %d\n", current->pid);
        return 0;
    }
#if __SULOG_GATE
    ksu_sulog_report_syscall(new_uid, NULL, "setuid", NULL);
#endif
    // umount the target mnt
    pr_info("handle umount for uid: %d, pid: %d\n", new_uid, current->pid);

    tw = kzalloc(sizeof(*tw), GFP_ATOMIC);
    if (!tw)
        return 0;

    tw->old_cred = get_current_cred();
    tw->cb.func = umount_tw_func;

    int err = task_work_add(current, &tw->cb, TWA_RESUME);
    if (err) {
        if (tw->old_cred) {
            put_cred(tw->old_cred);
        }
        kfree(tw);
        pr_warn("unmount add task_work failed\n");
    }

    return 0;
}

void ksu_kernel_umount_init(void)
{
    int rc = 0;
    rc = ksu_umount_manager_init();
    if (rc) {
        pr_err("Failed to initialize umount manager: %d\n", rc);
    }
    if (ksu_register_feature_handler(&kernel_umount_handler)) {
        pr_err("Failed to register kernel_umount feature handler\n");
    }
}

void ksu_kernel_umount_exit(void)
{
    ksu_unregister_feature_handler(KSU_FEATURE_KERNEL_UMOUNT);
}