[PATCH v2] binder: implement binderfs
Dan Carpenter
dan.carpenter at oracle.com
Fri Dec 14 07:11:23 UTC 2018
On Thu, Dec 13, 2018 at 10:59:11PM +0100, Christian Brauner wrote:
> +/**
> + * binderfs_new_inode - 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
> + * @device: binder device for which the new inode will be allocated
> + * @req: struct binderfs_device as copied from userspace
> + *
> + * This function will allocate a new inode from the super block of the
> + * filesystem mount and attach a dentry to that inode.
> + * 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.
> + *
> + * Return: 0 on success, negative errno on failure
> + */
> +static int binderfs_new_inode(struct inode *ref_inode,
> + struct binder_device *device,
> + struct binderfs_device __user *userp,
> + struct binderfs_device *req)
> +{
> + int minor, ret;
> + struct dentry *dentry, *dup, *root;
> + 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;
> + 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;
> + inode->i_private = device;
> +
> + name = kmalloc(name_len, GFP_KERNEL);
> + if (!name)
> + goto err;
> +
> + ret = snprintf(name, name_len, "%s", req->name);
> + if (ret < 0 || (size_t)ret >= name_len) {
kernel snprintf() doesn't return negatives and the cast isn't required
either.
> + ret = -EINVAL;
> + goto err;
> + }
> +
> + 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)
> + goto err;
copy_to_user() returns the number of bytes remaining.
ret = -EFAULT;
if (copy_to_user(userp, req, sizeof(*req)))
goto err;
Also if this copy_to_user() fails, then does the kfree(name) and the
iput(inode) lead to a double free of name in binderfs_evict_inode()?
> +
> + 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));
> + /*
> + * Prevent double free since iput() calls
> + * binderfs_evict_inode().
> + */
> + inode->i_private = NULL;
> + ret = -EEXIST;
> + goto err;
> + }
> + dput(dup);
> + }
> +
> + d_add(dentry, inode);
> + fsnotify_create(root->d_inode, dentry);
> + inode_unlock(d_inode(root));
> +
> + return 0;
> +
> +err:
> + kfree(name);
> + mutex_lock(&binderfs_minors_mutex);
> + ida_free(&binderfs_minors, minor);
> + mutex_unlock(&binderfs_minors_mutex);
> + iput(inode);
> +
> + return ret;
> +}
> +
> +static int binderfs_binder_device_create(struct inode *inode,
> + struct binderfs_device __user *userp,
> + struct binderfs_device *req)
> +{
> + struct binder_device *device;
> + int ret;
> +
> + device = kzalloc(sizeof(*device), GFP_KERNEL);
> + if (!device)
> + return -ENOMEM;
Just move this allocation into binderfs_new_inode() and get rid of this
function.
> +
> + ret = binderfs_new_inode(inode, device, userp, req);
> + if (ret < 0) {
> + kfree(device);
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +/**
> + * 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)
> +{
> + struct binderfs_info *info;
> + int ret = -EINVAL;
> + struct inode *inode = file_inode(file);
> + struct binderfs_device __user *device = (struct binderfs_device __user *)arg;
> + struct binderfs_device device_req;
> +
> + info = BINDERFS_I(inode);
info is not used.
> + switch (cmd) {
> + case BINDER_CTL_ADD:
> + ret = copy_from_user(&device_req, device, sizeof(device_req));
if (copy_from_user(&device_req, device, sizeof(device_req))) {
ret = -EFAULT;
break;
}
> + if (ret)
> + 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;
> + struct dentry *dentry;
> + struct binder_device *device;
> + int ret = 0;
> + 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 (info->control_dentry)
> + goto out;
I have a private static checker warning for gotos like this where we
don't set the error code before the goto out. Apparently here this
is a success path. I'm not an fs dev, so I don't know why this is a
success path. :( Maybe you could add a comment?
> +
> + 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;
> + inode->i_private = device;
> +
> + device->binderfs_inode = inode;
> + device->miscdev.minor = minor;
> +
> + dentry = d_alloc_name(root, "binder-control");
> + if (!dentry)
> + goto out;
> +
> + info->control_dentry = dentry;
> + d_add(dentry, inode);
> + inode_unlock(d_inode(root));
> +
> + return 0;
> +
> +out:
> + inode_unlock(d_inode(root));
> + kfree(device);
> + if (inode) {
> + inode->i_private = NULL;
> + 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)
> + return ret;
You can't return directly here, you need to goto the put_ipc_ns()
function in the error handling.
> +
> + 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:
> + if (inode)
> + iput(inode);
iput accepts NULL pointers.
> + kfree(info);
> + put_ipc_ns(ipc_ns);
> +
> + 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 < 0)
^^^^^^^
> + return ret;
> +
> + ret = register_filesystem(&binder_fs_type);
> + if (ret) {
^^^
These functions both return negative on error. From my static checker
perspective it's easiest if everyone checks "if (ret) " but either way
let's make it consistent.
> + 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);
Use gotos to unwind.
> + }
> +
> + return ret;
> +}
regards,
dan carpenter
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