// SPDX-License-Identifier: GPL-2.0-or-later /* Filesystem access-by-fd. * * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved. * Written by David Howells (dhowells@redhat.com) */ #include <linux/fs_context.h> #include <linux/fs_parser.h> #include <linux/slab.h> #include <linux/uaccess.h> #include <linux/syscalls.h> #include <linux/security.h> #include <linux/anon_inodes.h> #include <linux/namei.h> #include <linux/file.h> #include <uapi/linux/mount.h> #include "internal.h" #include "mount.h" /* * Allow the user to read back any error, warning or informational messages. */ static ssize_t fscontext_read(struct file *file, char __user *_buf, size_t len, loff_t *pos) { struct fs_context *fc = file->private_data; struct fc_log *log = fc->log.log; unsigned int logsize = ARRAY_SIZE(log->buffer); ssize_t ret; char *p; bool need_free; int index, n; ret = mutex_lock_interruptible(&fc->uapi_mutex); if (ret < 0) return ret; if (log->head == log->tail) { mutex_unlock(&fc->uapi_mutex); return -ENODATA; } index = log->tail & (logsize - 1); p = log->buffer[index]; need_free = log->need_free & (1 << index); log->buffer[index] = NULL; log->need_free &= ~(1 << index); log->tail++; mutex_unlock(&fc->uapi_mutex); ret = -EMSGSIZE; n = strlen(p); if (n > len) goto err_free; ret = -EFAULT; if (copy_to_user(_buf, p, n) != 0) goto err_free; ret = n; err_free: if (need_free) kfree(p); return ret; } static int fscontext_release(struct inode *inode, struct file *file) { struct fs_context *fc = file->private_data; if (fc) { file->private_data = NULL; put_fs_context(fc); } return 0; } const struct file_operations fscontext_fops = { .read = fscontext_read, .release = fscontext_release, .llseek = no_llseek, }; /* * Attach a filesystem context to a file and an fd. */ static int fscontext_create_fd(struct fs_context *fc, unsigned int o_flags) { int fd; fd = anon_inode_getfd("[fscontext]", &fscontext_fops, fc, O_RDWR | o_flags); if (fd < 0) put_fs_context(fc); return fd; } static int fscontext_alloc_log(struct fs_context *fc) { fc->log.log = kzalloc(sizeof(*fc->log.log), GFP_KERNEL); if (!fc->log.log) return -ENOMEM; refcount_set(&fc->log.log->usage, 1); fc->log.log->owner = fc->fs_type->owner; return 0; } /* * Open a filesystem by name so that it can be configured for mounting. * * We are allowed to specify a container in which the filesystem will be * opened, thereby indicating which namespaces will be used (notably, which * network namespace will be used for network filesystems). */ SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags) { struct file_system_type *fs_type; struct fs_context *fc; const char *fs_name; int ret; if (!may_mount()) return -EPERM; if (flags & ~FSOPEN_CLOEXEC) return -EINVAL; fs_name = strndup_user(_fs_name, PAGE_SIZE); if (IS_ERR(fs_name)) return PTR_ERR(fs_name); fs_type = get_fs_type(fs_name); kfree(fs_name); if (!fs_type) return -ENODEV; fc = fs_context_for_mount(fs_type, 0); put_filesystem(fs_type); if (IS_ERR(fc)) return PTR_ERR(fc); fc->phase = FS_CONTEXT_CREATE_PARAMS; ret = fscontext_alloc_log(fc); if (ret < 0) goto err_fc; return fscontext_create_fd(fc, flags & FSOPEN_CLOEXEC ? O_CLOEXEC : 0); err_fc: put_fs_context(fc); return ret; } /* * Pick a superblock into a context for reconfiguration. */ SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags) { struct fs_context *fc; struct path target; unsigned int lookup_flags; int ret; if (!may_mount()) return -EPERM; if ((flags & ~(FSPICK_CLOEXEC | FSPICK_SYMLINK_NOFOLLOW | FSPICK_NO_AUTOMOUNT | FSPICK_EMPTY_PATH)) != 0) return -EINVAL; lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT; if (flags & FSPICK_SYMLINK_NOFOLLOW) lookup_flags &= ~LOOKUP_FOLLOW; if (flags & FSPICK_NO_AUTOMOUNT) lookup_flags &= ~LOOKUP_AUTOMOUNT; if (flags & FSPICK_EMPTY_PATH) lookup_flags |= LOOKUP_EMPTY; ret = user_path_at(dfd, path, lookup_flags, &target); if (ret < 0) goto err; ret = -EINVAL; if (target.mnt->mnt_root != target.dentry) goto err_path; fc = fs_context_for_reconfigure(target.dentry, 0, 0); if (IS_ERR(fc)) { ret = PTR_ERR(fc); goto err_path; } fc->phase = FS_CONTEXT_RECONF_PARAMS; ret = fscontext_alloc_log(fc); if (ret < 0) goto err_fc; path_put(&target); return fscontext_create_fd(fc, flags & FSPICK_CLOEXEC ? O_CLOEXEC : 0); err_fc: put_fs_context(fc); err_path: path_put(&target); err: return ret; } /* * Check the state and apply the configuration. Note that this function is * allowed to 'steal' the value by setting param->xxx to NULL before returning. */ static int vfs_fsconfig_locked(struct fs_context *fc, int cmd, struct fs_parameter *param) { struct super_block *sb; int ret; ret = finish_clean_context(fc); if (ret) return ret; switch (cmd) { case FSCONFIG_CMD_CREATE: if (fc->phase != FS_CONTEXT_CREATE_PARAMS) return -EBUSY; if (!mount_capable(fc)) return -EPERM; fc->phase = FS_CONTEXT_CREATING; ret = vfs_get_tree(fc); if (ret) break; sb = fc->root->d_sb; ret = security_sb_kern_mount(sb); if (unlikely(ret)) { fc_drop_locked(fc); break; } up_write(&sb->s_umount); fc->phase = FS_CONTEXT_AWAITING_MOUNT; return 0; case FSCONFIG_CMD_RECONFIGURE: if (fc->phase != FS_CONTEXT_RECONF_PARAMS) return -EBUSY; fc->phase = FS_CONTEXT_RECONFIGURING; sb = fc->root->d_sb; if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) { ret = -EPERM; break; } down_write(&sb->s_umount); ret = reconfigure_super(fc); up_write(&sb->s_umount); if (ret) break; vfs_clean_context(fc); return 0; default: if (fc->phase != FS_CONTEXT_CREATE_PARAMS && fc->phase != FS_CONTEXT_RECONF_PARAMS) return -EBUSY; return vfs_parse_fs_param(fc, param); } fc->phase = FS_CONTEXT_FAILED; return ret; } /** * sys_fsconfig - Set parameters and trigger actions on a context * @fd: The filesystem context to act upon * @cmd: The action to take * @_key: Where appropriate, the parameter key to set * @_value: Where appropriate, the parameter value to set * @aux: Additional information for the value * * This system call is used to set parameters on a context, including * superblock settings, data source and security labelling. * * Actions include triggering the creation of a superblock and the * reconfiguration of the superblock attached to the specified context. * * When setting a parameter, @cmd indicates the type of value being proposed * and @_key indicates the parameter to be altered. * * @_value and @aux are used to specify the value, should a value be required: * * (*) fsconfig_set_flag: No value is specified. The parameter must be boolean * in nature. The key may be prefixed with "no" to invert the * setting. @_value must be NULL and @aux must be 0. * * (*) fsconfig_set_string: A string value is specified. The parameter can be * expecting boolean, integer, string or take a path. A conversion to an * appropriate type will be attempted (which may include looking up as a * path). @_value points to a NUL-terminated string and @aux must be 0. * * (*) fsconfig_set_binary: A binary blob is specified. @_value points to the * blob and @aux indicates its size. The parameter must be expecting a * blob. * * (*) fsconfig_set_path: A non-empty path is specified. The parameter must be * expecting a path object. @_value points to a NUL-terminated string that * is the path and @aux is a file descriptor at which to start a relative * lookup or AT_FDCWD. * * (*) fsconfig_set_path_empty: As fsconfig_set_path, but with AT_EMPTY_PATH * implied. * * (*) fsconfig_set_fd: An open file descriptor is specified. @_value must be * NULL and @aux indicates the file descriptor. */ SYSCALL_DEFINE5(fsconfig, int, fd, unsigned int, cmd, const char __user *, _key, const void __user *, _value, int, aux) { struct fs_context *fc; struct fd f; int ret; int lookup_flags = 0; struct fs_parameter param = { .type = fs_value_is_undefined, }; if (fd < 0) return -EINVAL; switch (cmd) { case FSCONFIG_SET_FLAG: if (!_key || _value || aux) return -EINVAL; break; case FSCONFIG_SET_STRING: if (!_key || !_value || aux) return -EINVAL; break; case FSCONFIG_SET_BINARY: if (!_key || !_value || aux <= 0 || aux > 1024 * 1024) return -EINVAL; break; case FSCONFIG_SET_PATH: case FSCONFIG_SET_PATH_EMPTY: if (!_key || !_value || (aux != AT_FDCWD && aux < 0)) return -EINVAL; break; case FSCONFIG_SET_FD: if (!_key || _value || aux < 0) return -EINVAL; break; case FSCONFIG_CMD_CREATE: case FSCONFIG_CMD_RECONFIGURE: if (_key || _value || aux) return -EINVAL; break; default: return -EOPNOTSUPP; } f = fdget(fd); if (!f.file) return -EBADF; ret = -EINVAL; if (f.file->f_op != &fscontext_fops) goto out_f; fc = f.file->private_data; if (fc->ops == &legacy_fs_context_ops) { switch (cmd) { case FSCONFIG_SET_BINARY: case FSCONFIG_SET_PATH: case FSCONFIG_SET_PATH_EMPTY: case FSCONFIG_SET_FD: ret = -EOPNOTSUPP; goto out_f; } } if (_key) { param.key = strndup_user(_key, 256); if (IS_ERR(param.key)) { ret = PTR_ERR(param.key); goto out_f; } } switch (cmd) { case FSCONFIG_SET_FLAG: param.type = fs_value_is_flag; break; case FSCONFIG_SET_STRING: param.type = fs_value_is_string; param.string = strndup_user(_value, 256); if (IS_ERR(param.string)) { ret = PTR_ERR(param.string); goto out_key; } param.size = strlen(param.string); break; case FSCONFIG_SET_BINARY: param.type = fs_value_is_blob; param.size = aux; param.blob = memdup_user_nul(_value, aux); if (IS_ERR(param.blob)) { ret = PTR_ERR(param.blob); goto out_key; } break; case FSCONFIG_SET_PATH_EMPTY: lookup_flags = LOOKUP_EMPTY; fallthrough; case FSCONFIG_SET_PATH: param.type = fs_value_is_filename; param.name = getname_flags(_value, lookup_flags, NULL); if (IS_ERR(param.name)) { ret = PTR_ERR(param.name); goto out_key; } param.dirfd = aux; param.size = strlen(param.name->name); break; case FSCONFIG_SET_FD: param.type = fs_value_is_file; ret = -EBADF; param.file = fget(aux); if (!param.file) goto out_key; break; default: break; } ret = mutex_lock_interruptible(&fc->uapi_mutex); if (ret == 0) { ret = vfs_fsconfig_locked(fc, cmd, ¶m); mutex_unlock(&fc->uapi_mutex); } /* Clean up the our record of any value that we obtained from * userspace. Note that the value may have been stolen by the LSM or * filesystem, in which case the value pointer will have been cleared. */ switch (cmd) { case FSCONFIG_SET_STRING: case FSCONFIG_SET_BINARY: kfree(param.string); break; case FSCONFIG_SET_PATH: case FSCONFIG_SET_PATH_EMPTY: if (param.name) putname(param.name); break; case FSCONFIG_SET_FD: if (param.file) fput(param.file); break; default: break; } out_key: kfree(param.key); out_f: fdput(f); return ret; }