diff options
Diffstat (limited to 'drivers/android/binderfs.c')
| -rw-r--r-- | drivers/android/binderfs.c | 544 |
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); |