1 files changed, 544 insertions, 0 deletions
diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
new file mode 100644
index 000000000000..7496b10532aa
--- /dev/null
+++ b/drivers/android/binderfs.c
@@ -0,0 +1,544 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/compiler_types.h>
+#include <linux/errno.h>
+#include <linux/fs.h>
+#include <linux/fsnotify.h>
+#include <linux/gfp.h>
+#include <linux/idr.h>
+#include <linux/init.h>
+#include <linux/ipc_namespace.h>
+#include <linux/kdev_t.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/magic.h>
+#include <linux/major.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/mount.h>
+#include <linux/parser.h>
+#include <linux/radix-tree.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/spinlock_types.h>
+#include <linux/stddef.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/uaccess.h>
+#include <linux/user_namespace.h>
+#include <linux/xarray.h>
+#include <uapi/asm-generic/errno-base.h>
+#include <uapi/linux/android/binder.h>
+#include <uapi/linux/android/binder_ctl.h>
+
+#include "binder_internal.h"
+
+#define FIRST_INODE 1
+#define SECOND_INODE 2
+#define INODE_OFFSET 3
+#define INTSTRLEN 21
+#define BINDERFS_MAX_MINOR (1U << MINORBITS)
+
+static struct vfsmount *binderfs_mnt;
+
+static dev_t binderfs_dev;
+static DEFINE_MUTEX(binderfs_minors_mutex);
+static DEFINE_IDA(binderfs_minors);
+
+/**
+ * binderfs_info - information about a binderfs mount
+ * @ipc_ns:         The ipc namespace the binderfs mount belongs to.
+ * @control_dentry: This records the dentry of this binderfs mount
+ *                  binder-control device.
+ * @root_uid:       uid that needs to be used when a new binder device is
+ *                  created.
+ * @root_gid:       gid that needs to be used when a new binder device is
+ *                  created.
+ */
+struct binderfs_info {
+	struct ipc_namespace *ipc_ns;
+	struct dentry *control_dentry;
+	kuid_t root_uid;
+	kgid_t root_gid;
+
+};
+
+static inline struct binderfs_info *BINDERFS_I(const struct inode *inode)
+{
+	return inode->i_sb->s_fs_info;
+}
+
+bool is_binderfs_device(const struct inode *inode)
+{
+	if (inode->i_sb->s_magic == BINDERFS_SUPER_MAGIC)
+		return true;
+
+	return false;
+}
+
+/**
+ * binderfs_binder_device_create - allocate inode from super block of a
+ *                                 binderfs mount
+ * @ref_inode: inode from wich the super block will be taken
+ * @userp:     buffer to copy information about new device for userspace to
+ * @req:       struct binderfs_device as copied from userspace
+ *
+ * This function allocated a new binder_device and reserves a new minor
+ * number for it.
+ * Minor numbers are limited and tracked globally in binderfs_minors. The
+ * function will stash a struct binder_device for the specific binder
+ * device in i_private of the inode.
+ * It will go on to allocate a new inode from the super block of the
+ * filesystem mount, stash a struct binder_device in its i_private field
+ * and attach a dentry to that inode.
+ *
+ * Return: 0 on success, negative errno on failure
+ */
+static int binderfs_binder_device_create(struct inode *ref_inode,
+					 struct binderfs_device __user *userp,
+					 struct binderfs_device *req)
+{
+	int minor, ret;
+	struct dentry *dentry, *dup, *root;
+	struct binder_device *device;
+	size_t name_len = BINDERFS_MAX_NAME + 1;
+	char *name = NULL;
+	struct inode *inode = NULL;
+	struct super_block *sb = ref_inode->i_sb;
+	struct binderfs_info *info = sb->s_fs_info;
+
+	/* Reserve new minor number for the new device. */
+	mutex_lock(&binderfs_minors_mutex);
+	minor = ida_alloc_max(&binderfs_minors, BINDERFS_MAX_MINOR, GFP_KERNEL);
+	mutex_unlock(&binderfs_minors_mutex);
+	if (minor < 0)
+		return minor;
+
+	ret = -ENOMEM;
+	device = kzalloc(sizeof(*device), GFP_KERNEL);
+	if (!device)
+		goto err;
+
+	inode = new_inode(sb);
+	if (!inode)
+		goto err;
+
+	inode->i_ino = minor + INODE_OFFSET;
+	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
+	init_special_inode(inode, S_IFCHR | 0600,
+			   MKDEV(MAJOR(binderfs_dev), minor));
+	inode->i_fop = &binder_fops;
+	inode->i_uid = info->root_uid;
+	inode->i_gid = info->root_gid;
+
+	name = kmalloc(name_len, GFP_KERNEL);
+	if (!name)
+		goto err;
+
+	strscpy(name, req->name, name_len);
+
+	device->binderfs_inode = inode;
+	device->context.binder_context_mgr_uid = INVALID_UID;
+	device->context.name = name;
+	device->miscdev.name = name;
+	device->miscdev.minor = minor;
+	mutex_init(&device->context.context_mgr_node_lock);
+
+	req->major = MAJOR(binderfs_dev);
+	req->minor = minor;
+
+	ret = copy_to_user(userp, req, sizeof(*req));
+	if (ret) {
+		ret = -EFAULT;
+		goto err;
+	}
+
+	root = sb->s_root;
+	inode_lock(d_inode(root));
+	dentry = d_alloc_name(root, name);
+	if (!dentry) {
+		inode_unlock(d_inode(root));
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	/* Verify that the name userspace gave us is not already in use. */
+	dup = d_lookup(root, &dentry->d_name);
+	if (dup) {
+		if (d_really_is_positive(dup)) {
+			dput(dup);
+			dput(dentry);
+			inode_unlock(d_inode(root));
+			ret = -EEXIST;
+			goto err;
+		}
+		dput(dup);
+	}
+
+	inode->i_private = device;
+	d_add(dentry, inode);
+	fsnotify_create(root->d_inode, dentry);
+	inode_unlock(d_inode(root));
+
+	return 0;
+
+err:
+	kfree(name);
+	kfree(device);
+	mutex_lock(&binderfs_minors_mutex);
+	ida_free(&binderfs_minors, minor);
+	mutex_unlock(&binderfs_minors_mutex);
+	iput(inode);
+
+	return ret;
+}
+
+/**
+ * binderfs_ctl_ioctl - handle binder device node allocation requests
+ *
+ * The request handler for the binder-control device. All requests operate on
+ * the binderfs mount the binder-control device resides in:
+ * - BINDER_CTL_ADD
+ *   Allocate a new binder device.
+ *
+ * Return: 0 on success, negative errno on failure
+ */
+static long binder_ctl_ioctl(struct file *file, unsigned int cmd,
+			     unsigned long arg)
+{
+	int ret = -EINVAL;
+	struct inode *inode = file_inode(file);
+	struct binderfs_device __user *device = (struct binderfs_device __user *)arg;
+	struct binderfs_device device_req;
+
+	switch (cmd) {
+	case BINDER_CTL_ADD:
+		ret = copy_from_user(&device_req, device, sizeof(device_req));
+		if (ret) {
+			ret = -EFAULT;
+			break;
+		}
+
+		ret = binderfs_binder_device_create(inode, device, &device_req);
+		break;
+	default:
+		break;
+	}
+
+	return ret;
+}
+
+static void binderfs_evict_inode(struct inode *inode)
+{
+	struct binder_device *device = inode->i_private;
+
+	clear_inode(inode);
+
+	if (!device)
+		return;
+
+	mutex_lock(&binderfs_minors_mutex);
+	ida_free(&binderfs_minors, device->miscdev.minor);
+	mutex_unlock(&binderfs_minors_mutex);
+
+	kfree(device->context.name);
+	kfree(device);
+}
+
+static const struct super_operations binderfs_super_ops = {
+	.statfs = simple_statfs,
+	.evict_inode = binderfs_evict_inode,
+};
+
+static int binderfs_rename(struct inode *old_dir, struct dentry *old_dentry,
+			   struct inode *new_dir, struct dentry *new_dentry,
+			   unsigned int flags)
+{
+	struct inode *inode = d_inode(old_dentry);
+
+	/* binderfs doesn't support directories. */
+	if (d_is_dir(old_dentry))
+		return -EPERM;
+
+	if (flags & ~RENAME_NOREPLACE)
+		return -EINVAL;
+
+	if (!simple_empty(new_dentry))
+		return -ENOTEMPTY;
+
+	if (d_really_is_positive(new_dentry))
+		simple_unlink(new_dir, new_dentry);
+
+	old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
+		new_dir->i_mtime = inode->i_ctime = current_time(old_dir);
+
+	return 0;
+}
+
+static int binderfs_unlink(struct inode *dir, struct dentry *dentry)
+{
+	/*
+	 * The control dentry is only ever touched during mount so checking it
+	 * here should not require us to take lock.
+	 */
+	if (BINDERFS_I(dir)->control_dentry == dentry)
+		return -EPERM;
+
+	return simple_unlink(dir, dentry);
+}
+
+static const struct file_operations binder_ctl_fops = {
+	.owner		= THIS_MODULE,
+	.open		= nonseekable_open,
+	.unlocked_ioctl	= binder_ctl_ioctl,
+	.compat_ioctl	= binder_ctl_ioctl,
+	.llseek		= noop_llseek,
+};
+
+/**
+ * binderfs_binder_ctl_create - create a new binder-control device
+ * @sb: super block of the binderfs mount
+ *
+ * This function creates a new binder-control device node in the binderfs mount
+ * referred to by @sb.
+ *
+ * Return: 0 on success, negative errno on failure
+ */
+static int binderfs_binder_ctl_create(struct super_block *sb)
+{
+	int minor, ret;
+	struct dentry *dentry;
+	struct binder_device *device;
+	struct inode *inode = NULL;
+	struct dentry *root = sb->s_root;
+	struct binderfs_info *info = sb->s_fs_info;
+
+	device = kzalloc(sizeof(*device), GFP_KERNEL);
+	if (!device)
+		return -ENOMEM;
+
+	inode_lock(d_inode(root));
+
+	/* If we have already created a binder-control node, return. */
+	if (info->control_dentry) {
+		ret = 0;
+		goto out;
+	}
+
+	ret = -ENOMEM;
+	inode = new_inode(sb);
+	if (!inode)
+		goto out;
+
+	/* Reserve a new minor number for the new device. */
+	mutex_lock(&binderfs_minors_mutex);
+	minor = ida_alloc_max(&binderfs_minors, BINDERFS_MAX_MINOR, GFP_KERNEL);
+	mutex_unlock(&binderfs_minors_mutex);
+	if (minor < 0) {
+		ret = minor;
+		goto out;
+	}
+
+	inode->i_ino = SECOND_INODE;
+	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
+	init_special_inode(inode, S_IFCHR | 0600,
+			   MKDEV(MAJOR(binderfs_dev), minor));
+	inode->i_fop = &binder_ctl_fops;
+	inode->i_uid = info->root_uid;
+	inode->i_gid = info->root_gid;
+
+	device->binderfs_inode = inode;
+	device->miscdev.minor = minor;
+
+	dentry = d_alloc_name(root, "binder-control");
+	if (!dentry)
+		goto out;
+
+	inode->i_private = device;
+	info->control_dentry = dentry;
+	d_add(dentry, inode);
+	inode_unlock(d_inode(root));
+
+	return 0;
+
+out:
+	inode_unlock(d_inode(root));
+	kfree(device);
+	iput(inode);
+
+	return ret;
+}
+
+static const struct inode_operations binderfs_dir_inode_operations = {
+	.lookup = simple_lookup,
+	.rename = binderfs_rename,
+	.unlink = binderfs_unlink,
+};
+
+static int binderfs_fill_super(struct super_block *sb, void *data, int silent)
+{
+	struct binderfs_info *info;
+	int ret = -ENOMEM;
+	struct inode *inode = NULL;
+	struct ipc_namespace *ipc_ns = sb->s_fs_info;
+
+	get_ipc_ns(ipc_ns);
+
+	sb->s_blocksize = PAGE_SIZE;
+	sb->s_blocksize_bits = PAGE_SHIFT;
+
+	/*
+	 * The binderfs filesystem can be mounted by userns root in a
+	 * non-initial userns. By default such mounts have the SB_I_NODEV flag
+	 * set in s_iflags to prevent security issues where userns root can
+	 * just create random device nodes via mknod() since it owns the
+	 * filesystem mount. But binderfs does not allow to create any files
+	 * including devices nodes. The only way to create binder devices nodes
+	 * is through the binder-control device which userns root is explicitly
+	 * allowed to do. So removing the SB_I_NODEV flag from s_iflags is both
+	 * necessary and safe.
+	 */
+	sb->s_iflags &= ~SB_I_NODEV;
+	sb->s_iflags |= SB_I_NOEXEC;
+	sb->s_magic = BINDERFS_SUPER_MAGIC;
+	sb->s_op = &binderfs_super_ops;
+	sb->s_time_gran = 1;
+
+	info = kzalloc(sizeof(struct binderfs_info), GFP_KERNEL);
+	if (!info)
+		goto err_without_dentry;
+
+	info->ipc_ns = ipc_ns;
+	info->root_gid = make_kgid(sb->s_user_ns, 0);
+	if (!gid_valid(info->root_gid))
+		info->root_gid = GLOBAL_ROOT_GID;
+	info->root_uid = make_kuid(sb->s_user_ns, 0);
+	if (!uid_valid(info->root_uid))
+		info->root_uid = GLOBAL_ROOT_UID;
+
+	sb->s_fs_info = info;
+
+	inode = new_inode(sb);
+	if (!inode)
+		goto err_without_dentry;
+
+	inode->i_ino = FIRST_INODE;
+	inode->i_fop = &simple_dir_operations;
+	inode->i_mode = S_IFDIR | 0755;
+	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
+	inode->i_op = &binderfs_dir_inode_operations;
+	set_nlink(inode, 2);
+
+	sb->s_root = d_make_root(inode);
+	if (!sb->s_root)
+		goto err_without_dentry;
+
+	ret = binderfs_binder_ctl_create(sb);
+	if (ret)
+		goto err_with_dentry;
+
+	return 0;
+
+err_with_dentry:
+	dput(sb->s_root);
+	sb->s_root = NULL;
+
+err_without_dentry:
+	put_ipc_ns(ipc_ns);
+	iput(inode);
+	kfree(info);
+
+	return ret;
+}
+
+static int binderfs_test_super(struct super_block *sb, void *data)
+{
+	struct binderfs_info *info = sb->s_fs_info;
+
+	if (info)
+		return info->ipc_ns == data;
+
+	return 0;
+}
+
+static int binderfs_set_super(struct super_block *sb, void *data)
+{
+	sb->s_fs_info = data;
+	return set_anon_super(sb, NULL);
+}
+
+static struct dentry *binderfs_mount(struct file_system_type *fs_type,
+				     int flags, const char *dev_name,
+				     void *data)
+{
+	struct super_block *sb;
+	struct ipc_namespace *ipc_ns = current->nsproxy->ipc_ns;
+
+	if (!ns_capable(ipc_ns->user_ns, CAP_SYS_ADMIN))
+		return ERR_PTR(-EPERM);
+
+	sb = sget_userns(fs_type, binderfs_test_super, binderfs_set_super,
+			 flags, ipc_ns->user_ns, ipc_ns);
+	if (IS_ERR(sb))
+		return ERR_CAST(sb);
+
+	if (!sb->s_root) {
+		int ret = binderfs_fill_super(sb, data, flags & SB_SILENT ? 1 : 0);
+		if (ret) {
+			deactivate_locked_super(sb);
+			return ERR_PTR(ret);
+		}
+
+		sb->s_flags |= SB_ACTIVE;
+	}
+
+	return dget(sb->s_root);
+}
+
+static void binderfs_kill_super(struct super_block *sb)
+{
+	struct binderfs_info *info = sb->s_fs_info;
+
+	if (info && info->ipc_ns)
+		put_ipc_ns(info->ipc_ns);
+
+	kfree(info);
+	kill_litter_super(sb);
+}
+
+static struct file_system_type binder_fs_type = {
+	.name		= "binder",
+	.mount		= binderfs_mount,
+	.kill_sb	= binderfs_kill_super,
+	.fs_flags	= FS_USERNS_MOUNT,
+};
+
+static int __init init_binderfs(void)
+{
+	int ret;
+
+	/* Allocate new major number for binderfs. */
+	ret = alloc_chrdev_region(&binderfs_dev, 0, BINDERFS_MAX_MINOR,
+				  "binder");
+	if (ret)
+		return ret;
+
+	ret = register_filesystem(&binder_fs_type);
+	if (ret) {
+		unregister_chrdev_region(binderfs_dev, BINDERFS_MAX_MINOR);
+		return ret;
+	}
+
+	binderfs_mnt = kern_mount(&binder_fs_type);
+	if (IS_ERR(binderfs_mnt)) {
+		ret = PTR_ERR(binderfs_mnt);
+		binderfs_mnt = NULL;
+		unregister_filesystem(&binder_fs_type);
+		unregister_chrdev_region(binderfs_dev, BINDERFS_MAX_MINOR);
+	}
+
+	return ret;
+}
+
+device_initcall(init_binderfs);