kernel: Implementing editable, removable mount points

kernel/umount_manager.c

@@ -0,0 +1,242 @@
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/uaccess.h>
+#include <linux/namei.h>
+#include <linux/path.h>
+#include <linux/mount.h>
+#include <linux/cred.h>
+
+#include "klog.h"
+#include "kernel_umount.h"
+#include "umount_manager.h"
+
+static struct umount_manager g_umount_mgr = {
+    .entry_count = 0,
+    .max_entries = 64,
+};
+
+static void try_umount_path(struct umount_entry *entry)
+{
+    try_umount(entry->path, entry->flags);
+}
+
+static struct umount_entry *find_entry_locked(const char *path)
+{
+    struct umount_entry *entry;
+
+    list_for_each_entry(entry, &g_umount_mgr.entry_list, list) {
+        if (strcmp(entry->path, path) == 0) {
+            return entry;
+        }
+    }
+
+    return NULL;
+}
+
+int ksu_umount_manager_init(void)
+{
+    INIT_LIST_HEAD(&g_umount_mgr.entry_list);
+    spin_lock_init(&g_umount_mgr.lock);
+
+    return 0;
+}
+
+void ksu_umount_manager_exit(void)
+{
+    struct umount_entry *entry, *tmp;
+    unsigned long flags;
+
+    spin_lock_irqsave(&g_umount_mgr.lock, flags);
+
+    list_for_each_entry_safe(entry, tmp, &g_umount_mgr.entry_list, list) {
+        list_del(&entry->list);
+        kfree(entry);
+        g_umount_mgr.entry_count--;
+    }
+
+    spin_unlock_irqrestore(&g_umount_mgr.lock, flags);
+
+    pr_info("Umount manager cleaned up\n");
+}
+
+int ksu_umount_manager_add(const char *path, int flags, bool is_default)
+{
+    struct umount_entry *entry;
+    unsigned long irqflags;
+    int ret = 0;
+
+    if (flags == -1)
+        flags = MNT_DETACH;
+
+    if (!path || strlen(path) == 0 || strlen(path) >= 256) {
+        return -EINVAL;
+    }
+
+    spin_lock_irqsave(&g_umount_mgr.lock, irqflags);
+
+    if (g_umount_mgr.entry_count >= g_umount_mgr.max_entries) {
+        pr_err("Umount manager: max entries reached\n");
+        ret = -ENOMEM;
+        goto out;
+    }
+
+    if (find_entry_locked(path)) {
+        pr_warn("Umount manager: path already exists: %s\n", path);
+        ret = -EEXIST;
+        goto out;
+    }
+
+    entry = kzalloc(sizeof(*entry), GFP_ATOMIC);
+    if (!entry) {
+        ret = -ENOMEM;
+        goto out;
+    }
+
+    strncpy(entry->path, path, sizeof(entry->path) - 1);
+    entry->flags = flags;
+    entry->state = UMOUNT_STATE_IDLE;
+    entry->is_default = is_default;
+    entry->ref_count = 0;
+
+    list_add_tail(&entry->list, &g_umount_mgr.entry_list);
+    g_umount_mgr.entry_count++;
+
+    pr_info("Umount manager: added %s entry: %s\n",
+            is_default ? "default" : "custom", path);
+
+out:
+    spin_unlock_irqrestore(&g_umount_mgr.lock, irqflags);
+    return ret;
+}
+
+int ksu_umount_manager_remove(const char *path)
+{
+    struct umount_entry *entry;
+    unsigned long flags;
+    int ret = 0;
+
+    if (!path) {
+        return -EINVAL;
+    }
+
+    spin_lock_irqsave(&g_umount_mgr.lock, flags);
+
+    entry = find_entry_locked(path);
+    if (!entry) {
+        ret = -ENOENT;
+        goto out;
+    }
+
+    if (entry->is_default) {
+        pr_err("Umount manager: cannot remove default entry: %s\n", path);
+        ret = -EPERM;
+        goto out;
+    }
+
+    if (entry->state == UMOUNT_STATE_BUSY || entry->ref_count > 0) {
+        pr_err("Umount manager: entry is busy: %s\n", path);
+        ret = -EBUSY;
+        goto out;
+    }
+
+    list_del(&entry->list);
+    g_umount_mgr.entry_count--;
+    kfree(entry);
+
+    pr_info("Umount manager: removed entry: %s\n", path);
+
+out:
+    spin_unlock_irqrestore(&g_umount_mgr.lock, flags);
+    return ret;
+}
+
+void ksu_umount_manager_execute_all(const struct cred *cred)
+{
+    struct umount_entry *entry;
+    unsigned long flags;
+
+    spin_lock_irqsave(&g_umount_mgr.lock, flags);
+
+    list_for_each_entry(entry, &g_umount_mgr.entry_list, list) {
+        if (entry->state == UMOUNT_STATE_IDLE) {
+            entry->ref_count++;
+        }
+    }
+
+    spin_unlock_irqrestore(&g_umount_mgr.lock, flags);
+
+    list_for_each_entry(entry, &g_umount_mgr.entry_list, list) {
+        if (entry->ref_count > 0 && entry->state == UMOUNT_STATE_IDLE) {
+            try_umount_path(entry);
+        }
+    }
+
+    spin_lock_irqsave(&g_umount_mgr.lock, flags);
+
+    list_for_each_entry(entry, &g_umount_mgr.entry_list, list) {
+        if (entry->ref_count > 0) {
+            entry->ref_count--;
+        }
+    }
+
+    spin_unlock_irqrestore(&g_umount_mgr.lock, flags);
+}
+
+int ksu_umount_manager_get_entries(struct ksu_umount_entry_info __user *entries, u32 *count)
+{
+    struct umount_entry *entry;
+    struct ksu_umount_entry_info info;
+    unsigned long flags;
+    u32 idx = 0;
+    u32 max_count = *count;
+
+    spin_lock_irqsave(&g_umount_mgr.lock, flags);
+
+    list_for_each_entry(entry, &g_umount_mgr.entry_list, list) {
+        if (idx >= max_count) {
+            break;
+        }
+
+        memset(&info, 0, sizeof(info));
+        strncpy(info.path, entry->path, sizeof(info.path) - 1);
+        info.flags = entry->flags;
+        info.is_default = entry->is_default;
+        info.state = entry->state;
+        info.ref_count = entry->ref_count;
+
+        if (copy_to_user(&entries[idx], &info, sizeof(info))) {
+            spin_unlock_irqrestore(&g_umount_mgr.lock, flags);
+            return -EFAULT;
+        }
+
+        idx++;
+    }
+
+    *count = idx;
+
+    spin_unlock_irqrestore(&g_umount_mgr.lock, flags);
+    return 0;
+}
+
+int ksu_umount_manager_clear_custom(void)
+{
+    struct umount_entry *entry, *tmp;
+    unsigned long flags;
+    u32 cleared = 0;
+
+    spin_lock_irqsave(&g_umount_mgr.lock, flags);
+
+    list_for_each_entry_safe(entry, tmp, &g_umount_mgr.entry_list, list) {
+        if (!entry->is_default && entry->state == UMOUNT_STATE_IDLE && entry->ref_count == 0) {
+            list_del(&entry->list);
+            kfree(entry);
+            g_umount_mgr.entry_count--;
+            cleared++;
+        }
+    }
+
+    spin_unlock_irqrestore(&g_umount_mgr.lock, flags);
+
+    pr_info("Umount manager: cleared %u custom entries\n", cleared);
+    return 0;
+}