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linux
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inode.c
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// SPDX-License-Identifier: GPL-2.0-only /* * inode.c - part of tracefs, a pseudo file system for activating tracing * * Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com> * * Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com> * * tracefs is the file system that is used by the tracing infrastructure. */ #include <linux/module.h> #include <linux/fs.h> #include <linux/mount.h> #include <linux/kobject.h> #include <linux/namei.h> #include <linux/tracefs.h> #include <linux/fsnotify.h> #include <linux/security.h> #include <linux/seq_file.h> #include <linux/parser.h> #include <linux/magic.h> #include <linux/slab.h> #define TRACEFS_DEFAULT_MODE 0700 static struct vfsmount *tracefs_mount; static int tracefs_mount_count; static bool tracefs_registered; static ssize_t default_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos) { return 0; } static ssize_t default_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos) { return count; } static const struct file_operations tracefs_file_operations = { .read = default_read_file, .write = default_write_file, .open = simple_open, .llseek = noop_llseek, }; static struct tracefs_dir_ops { int (*mkdir)(const char *name); int (*rmdir)(const char *name); } tracefs_ops __ro_after_init; static char *get_dname(struct dentry *dentry) { const char *dname; char *name; int len = dentry->d_name.len; dname = dentry->d_name.name; name = kmalloc(len + 1, GFP_KERNEL); if (!name) return NULL; memcpy(name, dname, len); name[len] = 0; return name; } static int tracefs_syscall_mkdir(struct user_namespace *mnt_userns, struct inode *inode, struct dentry *dentry, umode_t mode) { char *name; int ret; name = get_dname(dentry); if (!name) return -ENOMEM; /* * The mkdir call can call the generic functions that create * the files within the tracefs system. It is up to the individual * mkdir routine to handle races. */ inode_unlock(inode); ret = tracefs_ops.mkdir(name); inode_lock(inode); kfree(name); return ret; } static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry) { char *name; int ret; name = get_dname(dentry); if (!name) return -ENOMEM; /* * The rmdir call can call the generic functions that create * the files within the tracefs system. It is up to the individual * rmdir routine to handle races. * This time we need to unlock not only the parent (inode) but * also the directory that is being deleted. */ inode_unlock(inode); inode_unlock(d_inode(dentry)); ret = tracefs_ops.rmdir(name); inode_lock_nested(inode, I_MUTEX_PARENT); inode_lock(d_inode(dentry)); kfree(name); return ret; } static const struct inode_operations tracefs_dir_inode_operations = { .lookup = simple_lookup, .mkdir = tracefs_syscall_mkdir, .rmdir = tracefs_syscall_rmdir, }; static struct inode *tracefs_get_inode(struct super_block *sb) { struct inode *inode = new_inode(sb); if (inode) { inode->i_ino = get_next_ino(); inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode); } return inode; } struct tracefs_mount_opts { kuid_t uid; kgid_t gid; umode_t mode; }; enum { Opt_uid, Opt_gid, Opt_mode, Opt_err }; static const match_table_t tokens = { {Opt_uid, "uid=%u"}, {Opt_gid, "gid=%u"}, {Opt_mode, "mode=%o"}, {Opt_err, NULL} }; struct tracefs_fs_info { struct tracefs_mount_opts mount_opts; }; static void change_gid(struct dentry *dentry, kgid_t gid) { if (!dentry->d_inode) return; dentry->d_inode->i_gid = gid; } /* * Taken from d_walk, but without he need for handling renames. * Nothing can be renamed while walking the list, as tracefs * does not support renames. This is only called when mounting * or remounting the file system, to set all the files to * the given gid. */ static void set_gid(struct dentry *parent, kgid_t gid) { struct dentry *this_parent; struct list_head *next; this_parent = parent; spin_lock(&this_parent->d_lock); change_gid(this_parent, gid); repeat: next = this_parent->d_subdirs.next; resume: while (next != &this_parent->d_subdirs) { struct list_head *tmp = next; struct dentry *dentry = list_entry(tmp, struct dentry, d_child); next = tmp->next; spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED); change_gid(dentry, gid); if (!list_empty(&dentry->d_subdirs)) { spin_unlock(&this_parent->d_lock); spin_release(&dentry->d_lock.dep_map, _RET_IP_); this_parent = dentry; spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_); goto repeat; } spin_unlock(&dentry->d_lock); } /* * All done at this level ... ascend and resume the search. */ rcu_read_lock(); ascend: if (this_parent != parent) { struct dentry *child = this_parent; this_parent = child->d_parent; spin_unlock(&child->d_lock); spin_lock(&this_parent->d_lock); /* go into the first sibling still alive */ do { next = child->d_child.next; if (next == &this_parent->d_subdirs) goto ascend; child = list_entry(next, struct dentry, d_child); } while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED)); rcu_read_unlock(); goto resume; } rcu_read_unlock(); spin_unlock(&this_parent->d_lock); return; } static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts) { substring_t args[MAX_OPT_ARGS]; int option; int token; kuid_t uid; kgid_t gid; char *p; opts->mode = TRACEFS_DEFAULT_MODE; while ((p = strsep(&data, ",")) != NULL) { if (!*p) continue; token = match_token(p, tokens, args); switch (token) { case Opt_uid: if (match_int(&args[0], &option)) return -EINVAL; uid = make_kuid(current_user_ns(), option); if (!uid_valid(uid)) return -EINVAL; opts->uid = uid; break; case Opt_gid: if (match_int(&args[0], &option)) return -EINVAL; gid = make_kgid(current_user_ns(), option); if (!gid_valid(gid)) return -EINVAL; opts->gid = gid; break; case Opt_mode: if (match_octal(&args[0], &option)) return -EINVAL; opts->mode = option & S_IALLUGO; break; /* * We might like to report bad mount options here; * but traditionally tracefs has ignored all mount options */ } } return 0; } static int tracefs_apply_options(struct super_block *sb) { struct tracefs_fs_info *fsi = sb->s_fs_info; struct inode *inode = d_inode(sb->s_root); struct tracefs_mount_opts *opts = &fsi->mount_opts; inode->i_mode &= ~S_IALLUGO; inode->i_mode |= opts->mode; inode->i_uid = opts->uid; /* Set all the group ids to the mount option */ set_gid(sb->s_root, opts->gid); return 0; } static int tracefs_remount(struct super_block *sb, int *flags, char *data) { int err; struct tracefs_fs_info *fsi = sb->s_fs_info; sync_filesystem(sb); err = tracefs_parse_options(data, &fsi->mount_opts); if (err) goto fail; tracefs_apply_options(sb); fail: return err; } static int tracefs_show_options(struct seq_file *m, struct dentry *root) { struct tracefs_fs_info *fsi = root->d_sb->s_fs_info; struct tracefs_mount_opts *opts = &fsi->mount_opts; if (!uid_eq(opts->uid, GLOBAL_ROOT_UID)) seq_printf(m, ",uid=%u", from_kuid_munged(&init_user_ns, opts->uid)); if (!gid_eq(opts->gid, GLOBAL_ROOT_GID)) seq_printf(m, ",gid=%u", from_kgid_munged(&init_user_ns, opts->gid)); if (opts->mode != TRACEFS_DEFAULT_MODE) seq_printf(m, ",mode=%o", opts->mode); return 0; } static const struct super_operations tracefs_super_operations = { .statfs = simple_statfs, .remount_fs = tracefs_remount, .show_options = tracefs_show_options, }; static int trace_fill_super(struct super_block *sb, void *data, int silent) { static const struct tree_descr trace_files[] = {{""}}; struct tracefs_fs_info *fsi; int err; fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL); sb->s_fs_info = fsi; if (!fsi) { err = -ENOMEM; goto fail; } err = tracefs_parse_options(data, &fsi->mount_opts); if (err) goto fail; err = simple_fill_super(sb, TRACEFS_MAGIC, trace_files); if (err) goto fail; sb->s_op = &tracefs_super_operations; tracefs_apply_options(sb); return 0; fail: kfree(fsi); sb->s_fs_info = NULL; return err; } static struct dentry *trace_mount(struct file_system_type *fs_type, int flags, const char *dev_name, void *data) { return mount_single(fs_type, flags, data, trace_fill_super); } static struct file_system_type trace_fs_type = { .owner = THIS_MODULE, .name = "tracefs", .mount = trace_mount, .kill_sb = kill_litter_super, }; MODULE_ALIAS_FS("tracefs"); static struct dentry *start_creating(const char *name, struct dentry *parent) { struct dentry *dentry; int error; pr_debug("tracefs: creating file '%s'\n",name); error = simple_pin_fs(&trace_fs_type, &tracefs_mount, &tracefs_mount_count); if (error) return ERR_PTR(error); /* If the parent is not specified, we create it in the root. * We need the root dentry to do this, which is in the super * block. A pointer to that is in the struct vfsmount that we * have around. */ if (!parent) parent = tracefs_mount->mnt_root; inode_lock(d_inode(parent)); if (unlikely(IS_DEADDIR(d_inode(parent)))) dentry = ERR_PTR(-ENOENT); else dentry = lookup_one_len(name, parent, strlen(name)); if (!IS_ERR(dentry) && d_inode(dentry)) { dput(dentry); dentry = ERR_PTR(-EEXIST); } if (IS_ERR(dentry)) { inode_unlock(d_inode(parent)); simple_release_fs(&tracefs_mount, &tracefs_mount_count); } return dentry; } static struct dentry *failed_creating(struct dentry *dentry) { inode_unlock(d_inode(dentry->d_parent)); dput(dentry); simple_release_fs(&tracefs_mount, &tracefs_mount_count); return NULL; } static struct dentry *end_creating(struct dentry *dentry) { inode_unlock(d_inode(dentry->d_parent)); return dentry; } /** * tracefs_create_file - create a file in the tracefs filesystem * @name: a pointer to a string containing the name of the file to create. * @mode: the permission that the file should have. * @parent: a pointer to the parent dentry for this file. This should be a * directory dentry if set. If this parameter is NULL, then the * file will be created in the root of the tracefs filesystem. * @data: a pointer to something that the caller will want to get to later * on. The inode.i_private pointer will point to this value on * the open() call. * @fops: a pointer to a struct file_operations that should be used for * this file. * * This is the basic "create a file" function for tracefs. It allows for a * wide range of flexibility in creating a file, or a directory (if you want * to create a directory, the tracefs_create_dir() function is * recommended to be used instead.) * * This function will return a pointer to a dentry if it succeeds. This * pointer must be passed to the tracefs_remove() function when the file is * to be removed (no automatic cleanup happens if your module is unloaded, * you are responsible here.) If an error occurs, %NULL will be returned. * * If tracefs is not enabled in the kernel, the value -%ENODEV will be * returned. */ struct dentry *tracefs_create_file(const char *name, umode_t mode, struct dentry *parent, void *data, const struct file_operations *fops) { struct dentry *dentry; struct inode *inode; if (security_locked_down(LOCKDOWN_TRACEFS)) return NULL; if (!(mode & S_IFMT)) mode |= S_IFREG; BUG_ON(!S_ISREG(mode)); dentry = start_creating(name, parent); if (IS_ERR(dentry)) return NULL; inode = tracefs_get_inode(dentry->d_sb); if (unlikely(!inode)) return failed_creating(dentry); inode->i_mode = mode; inode->i_fop = fops ? fops : &tracefs_file_operations; inode->i_private = data; inode->i_uid = d_inode(dentry->d_parent)->i_uid; inode->i_gid = d_inode(dentry->d_parent)->i_gid; d_instantiate(dentry, inode); fsnotify_create(d_inode(dentry->d_parent), dentry); return end_creating(dentry); } static struct dentry *__create_dir(const char *name, struct dentry *parent, const struct inode_operations *ops) { struct dentry *dentry = start_creating(name, parent); struct inode *inode; if (IS_ERR(dentry)) return NULL; inode = tracefs_get_inode(dentry->d_sb); if (unlikely(!inode)) return failed_creating(dentry); /* Do not set bits for OTH */ inode->i_mode = S_IFDIR | S_IRWXU | S_IRUSR| S_IRGRP | S_IXUSR | S_IXGRP; inode->i_op = ops; inode->i_fop = &simple_dir_operations; inode->i_uid = d_inode(dentry->d_parent)->i_uid; inode->i_gid = d_inode(dentry->d_parent)->i_gid; /* directory inodes start off with i_nlink == 2 (for "." entry) */ inc_nlink(inode); d_instantiate(dentry, inode); inc_nlink(d_inode(dentry->d_parent)); fsnotify_mkdir(d_inode(dentry->d_parent), dentry); return end_creating(dentry); } /** * tracefs_create_dir - create a directory in the tracefs filesystem * @name: a pointer to a string containing the name of the directory to * create. * @parent: a pointer to the parent dentry for this file. This should be a * directory dentry if set. If this parameter is NULL, then the * directory will be created in the root of the tracefs filesystem. * * This function creates a directory in tracefs with the given name. * * This function will return a pointer to a dentry if it succeeds. This * pointer must be passed to the tracefs_remove() function when the file is * to be removed. If an error occurs, %NULL will be returned. * * If tracing is not enabled in the kernel, the value -%ENODEV will be * returned. */ struct dentry *tracefs_create_dir(const char *name, struct dentry *parent) { return __create_dir(name, parent, &simple_dir_inode_operations); } /** * tracefs_create_instance_dir - create the tracing instances directory * @name: The name of the instances directory to create * @parent: The parent directory that the instances directory will exist * @mkdir: The function to call when a mkdir is performed. * @rmdir: The function to call when a rmdir is performed. * * Only one instances directory is allowed. * * The instances directory is special as it allows for mkdir and rmdir to * to be done by userspace. When a mkdir or rmdir is performed, the inode * locks are released and the methods passed in (@mkdir and @rmdir) are * called without locks and with the name of the directory being created * within the instances directory. * * Returns the dentry of the instances directory. */ __init struct dentry *tracefs_create_instance_dir(const char *name, struct dentry *parent, int (*mkdir)(const char *name), int (*rmdir)(const char *name)) { struct dentry *dentry; /* Only allow one instance of the instances directory. */ if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir)) return NULL; dentry = __create_dir(name, parent, &tracefs_dir_inode_operations); if (!dentry) return NULL; tracefs_ops.mkdir = mkdir; tracefs_ops.rmdir = rmdir; return dentry; } static void remove_one(struct dentry *victim) { simple_release_fs(&tracefs_mount, &tracefs_mount_count); } /** * tracefs_remove - recursively removes a directory * @dentry: a pointer to a the dentry of the directory to be removed. * * This function recursively removes a directory tree in tracefs that * was previously created with a call to another tracefs function * (like tracefs_create_file() or variants thereof.) */ void tracefs_remove(struct dentry *dentry) { if (IS_ERR_OR_NULL(dentry)) return; simple_pin_fs(&trace_fs_type, &tracefs_mount, &tracefs_mount_count); simple_recursive_removal(dentry, remove_one); simple_release_fs(&tracefs_mount, &tracefs_mount_count); } /** * tracefs_initialized - Tells whether tracefs has been registered */ bool tracefs_initialized(void) { return tracefs_registered; } static int __init tracefs_init(void) { int retval; retval = sysfs_create_mount_point(kernel_kobj, "tracing"); if (retval) return -EINVAL; retval = register_filesystem(&trace_fs_type); if (!retval) tracefs_registered = true; return retval; } core_initcall(tracefs_init);
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