/* -*- linux-c -*- --------------------------------------------------------- * * * linux/fs/devpts/inode.c * * Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved * * This file is part of the Linux kernel and is made available under * the terms of the GNU General Public License, version 2, or at your * option, any later version, incorporated herein by reference. * * ------------------------------------------------------------------------- */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include <linux/module.h> #include <linux/init.h> #include <linux/fs.h> #include <linux/sched.h> #include <linux/namei.h> #include <linux/slab.h> #include <linux/mount.h> #include <linux/tty.h> #include <linux/mutex.h> #include <linux/magic.h> #include <linux/idr.h> #include <linux/devpts_fs.h> #include <linux/parser.h> #include <linux/fsnotify.h> #include <linux/seq_file.h> #define DEVPTS_DEFAULT_MODE 0600 /* * ptmx is a new node in /dev/pts and will be unused in legacy (single- * instance) mode. To prevent surprises in user space, set permissions of * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful * permissions. */ #define DEVPTS_DEFAULT_PTMX_MODE 0000 #define PTMX_MINOR 2 /* * sysctl support for setting limits on the number of Unix98 ptys allocated. * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly. */ static int pty_limit = NR_UNIX98_PTY_DEFAULT; static int pty_reserve = NR_UNIX98_PTY_RESERVE; static int pty_limit_min; static int pty_limit_max = INT_MAX; static int pty_count; static struct ctl_table pty_table[] = { { .procname = "max", .maxlen = sizeof(int), .mode = 0644, .data = &pty_limit, .proc_handler = proc_dointvec_minmax, .extra1 = &pty_limit_min, .extra2 = &pty_limit_max, }, { .procname = "reserve", .maxlen = sizeof(int), .mode = 0644, .data = &pty_reserve, .proc_handler = proc_dointvec_minmax, .extra1 = &pty_limit_min, .extra2 = &pty_limit_max, }, { .procname = "nr", .maxlen = sizeof(int), .mode = 0444, .data = &pty_count, .proc_handler = proc_dointvec, }, {} }; static struct ctl_table pty_kern_table[] = { { .procname = "pty", .mode = 0555, .child = pty_table, }, {} }; static struct ctl_table pty_root_table[] = { { .procname = "kernel", .mode = 0555, .child = pty_kern_table, }, {} }; static DEFINE_MUTEX(allocated_ptys_lock); static struct vfsmount *devpts_mnt; struct pts_mount_opts { int setuid; int setgid; kuid_t uid; kgid_t gid; umode_t mode; umode_t ptmxmode; int newinstance; int max; }; enum { Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max, Opt_err }; static const match_table_t tokens = { {Opt_uid, "uid=%u"}, {Opt_gid, "gid=%u"}, {Opt_mode, "mode=%o"}, #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES {Opt_ptmxmode, "ptmxmode=%o"}, {Opt_newinstance, "newinstance"}, {Opt_max, "max=%d"}, #endif {Opt_err, NULL} }; struct pts_fs_info { struct ida allocated_ptys; struct pts_mount_opts mount_opts; struct dentry *ptmx_dentry; }; static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb) { return sb->s_fs_info; } static inline struct super_block *pts_sb_from_inode(struct inode *inode) { #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC) return inode->i_sb; #endif return devpts_mnt->mnt_sb; } #define PARSE_MOUNT 0 #define PARSE_REMOUNT 1 /* * parse_mount_options(): * Set @opts to mount options specified in @data. If an option is not * specified in @data, set it to its default value. The exception is * 'newinstance' option which can only be set/cleared on a mount (i.e. * cannot be changed during remount). * * Note: @data may be NULL (in which case all options are set to default). */ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts) { char *p; kuid_t uid; kgid_t gid; opts->setuid = 0; opts->setgid = 0; opts->uid = GLOBAL_ROOT_UID; opts->gid = GLOBAL_ROOT_GID; opts->mode = DEVPTS_DEFAULT_MODE; opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE; opts->max = NR_UNIX98_PTY_MAX; /* newinstance makes sense only on initial mount */ if (op == PARSE_MOUNT) opts->newinstance = 0; while ((p = strsep(&data, ",")) != NULL) { substring_t args[MAX_OPT_ARGS]; int token; int option; 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; opts->setuid = 1; 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; opts->setgid = 1; break; case Opt_mode: if (match_octal(&args[0], &option)) return -EINVAL; opts->mode = option & S_IALLUGO; break; #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES case Opt_ptmxmode: if (match_octal(&args[0], &option)) return -EINVAL; opts->ptmxmode = option & S_IALLUGO; break; case Opt_newinstance: /* newinstance makes sense only on initial mount */ if (op == PARSE_MOUNT) opts->newinstance = 1; break; case Opt_max: if (match_int(&args[0], &option) || option < 0 || option > NR_UNIX98_PTY_MAX) return -EINVAL; opts->max = option; break; #endif default: pr_err("called with bogus options\n"); return -EINVAL; } } return 0; } #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES static int mknod_ptmx(struct super_block *sb) { int mode; int rc = -ENOMEM; struct dentry *dentry; struct inode *inode; struct dentry *root = sb->s_root; struct pts_fs_info *fsi = DEVPTS_SB(sb); struct pts_mount_opts *opts = &fsi->mount_opts; kuid_t root_uid; kgid_t root_gid; root_uid = make_kuid(current_user_ns(), 0); root_gid = make_kgid(current_user_ns(), 0); if (!uid_valid(root_uid) || !gid_valid(root_gid)) return -EINVAL; mutex_lock(&root->d_inode->i_mutex); /* If we have already created ptmx node, return */ if (fsi->ptmx_dentry) { rc = 0; goto out; } dentry = d_alloc_name(root, "ptmx"); if (!dentry) { pr_err("Unable to alloc dentry for ptmx node\n"); goto out; } /* * Create a new 'ptmx' node in this mount of devpts. */ inode = new_inode(sb); if (!inode) { pr_err("Unable to alloc inode for ptmx node\n"); dput(dentry); goto out; } inode->i_ino = 2; inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; mode = S_IFCHR|opts->ptmxmode; init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2)); inode->i_uid = root_uid; inode->i_gid = root_gid; d_add(dentry, inode); fsi->ptmx_dentry = dentry; rc = 0; out: mutex_unlock(&root->d_inode->i_mutex); return rc; } static void update_ptmx_mode(struct pts_fs_info *fsi) { struct inode *inode; if (fsi->ptmx_dentry) { inode = fsi->ptmx_dentry->d_inode; inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode; } } #else static inline void update_ptmx_mode(struct pts_fs_info *fsi) { return; } #endif static int devpts_remount(struct super_block *sb, int *flags, char *data) { int err; struct pts_fs_info *fsi = DEVPTS_SB(sb); struct pts_mount_opts *opts = &fsi->mount_opts; sync_filesystem(sb); err = parse_mount_options(data, PARSE_REMOUNT, opts); /* * parse_mount_options() restores options to default values * before parsing and may have changed ptmxmode. So, update the * mode in the inode too. Bogus options don't fail the remount, * so do this even on error return. */ update_ptmx_mode(fsi); return err; } static int devpts_show_options(struct seq_file *seq, struct dentry *root) { struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb); struct pts_mount_opts *opts = &fsi->mount_opts; if (opts->setuid) seq_printf(seq, ",uid=%u", from_kuid_munged(&init_user_ns, opts->uid)); if (opts->setgid) seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, opts->gid)); seq_printf(seq, ",mode=%03o", opts->mode); #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode); if (opts->max < NR_UNIX98_PTY_MAX) seq_printf(seq, ",max=%d", opts->max); #endif return 0; } static const struct super_operations devpts_sops = { .statfs = simple_statfs, .remount_fs = devpts_remount, .show_options = devpts_show_options, }; static void *new_pts_fs_info(void) { struct pts_fs_info *fsi; fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL); if (!fsi) return NULL; ida_init(&fsi->allocated_ptys); fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE; fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE; return fsi; } static int devpts_fill_super(struct super_block *s, void *data, int silent) { struct inode *inode; s->s_blocksize = 1024; s->s_blocksize_bits = 10; s->s_magic = DEVPTS_SUPER_MAGIC; s->s_op = &devpts_sops; s->s_time_gran = 1; s->s_fs_info = new_pts_fs_info(); if (!s->s_fs_info) goto fail; inode = new_inode(s); if (!inode) goto fail; inode->i_ino = 1; inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR; inode->i_op = &simple_dir_inode_operations; inode->i_fop = &simple_dir_operations; set_nlink(inode, 2); s->s_root = d_make_root(inode); if (s->s_root) return 0; pr_err("get root dentry failed\n"); fail: return -ENOMEM; } #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES static int compare_init_pts_sb(struct super_block *s, void *p) { if (devpts_mnt) return devpts_mnt->mnt_sb == s; return 0; } /* * devpts_mount() * * If the '-o newinstance' mount option was specified, mount a new * (private) instance of devpts. PTYs created in this instance are * independent of the PTYs in other devpts instances. * * If the '-o newinstance' option was not specified, mount/remount the * initial kernel mount of devpts. This type of mount gives the * legacy, single-instance semantics. * * The 'newinstance' option is needed to support multiple namespace * semantics in devpts while preserving backward compatibility of the * current 'single-namespace' semantics. i.e all mounts of devpts * without the 'newinstance' mount option should bind to the initial * kernel mount, like mount_single(). * * Mounts with 'newinstance' option create a new, private namespace. * * NOTE: * * For single-mount semantics, devpts cannot use mount_single(), * because mount_single()/sget() find and use the super-block from * the most recent mount of devpts. But that recent mount may be a * 'newinstance' mount and mount_single() would pick the newinstance * super-block instead of the initial super-block. */ static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags, const char *dev_name, void *data) { int error; struct pts_mount_opts opts; struct super_block *s; error = parse_mount_options(data, PARSE_MOUNT, &opts); if (error) return ERR_PTR(error); /* Require newinstance for all user namespace mounts to ensure * the mount options are not changed. */ if ((current_user_ns() != &init_user_ns) && !opts.newinstance) return ERR_PTR(-EINVAL); if (opts.newinstance) s = sget(fs_type, NULL, set_anon_super, flags, NULL); else s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags, NULL); if (IS_ERR(s)) return ERR_CAST(s); if (!s->s_root) { error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0); if (error) goto out_undo_sget; s->s_flags |= MS_ACTIVE; } memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts)); error = mknod_ptmx(s); if (error) goto out_undo_sget; return dget(s->s_root); out_undo_sget: deactivate_locked_super(s); return ERR_PTR(error); } #else /* * This supports only the legacy single-instance semantics (no * multiple-instance semantics) */ static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags, const char *dev_name, void *data) { return mount_single(fs_type, flags, data, devpts_fill_super); } #endif static void devpts_kill_sb(struct super_block *sb) { struct pts_fs_info *fsi = DEVPTS_SB(sb); ida_destroy(&fsi->allocated_ptys); kfree(fsi); kill_litter_super(sb); } static struct file_system_type devpts_fs_type = { .name = "devpts", .mount = devpts_mount, .kill_sb = devpts_kill_sb, #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES .fs_flags = FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT, #endif }; /* * The normal naming convention is simply /dev/pts/<number>; this conforms * to the System V naming convention */ int devpts_new_index(struct inode *ptmx_inode) { struct super_block *sb = pts_sb_from_inode(ptmx_inode); struct pts_fs_info *fsi = DEVPTS_SB(sb); int index; int ida_ret; retry: if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL)) return -ENOMEM; mutex_lock(&allocated_ptys_lock); if (pty_count >= pty_limit - (fsi->mount_opts.newinstance ? pty_reserve : 0)) { mutex_unlock(&allocated_ptys_lock); return -ENOSPC; } ida_ret = ida_get_new(&fsi->allocated_ptys, &index); if (ida_ret < 0) { mutex_unlock(&allocated_ptys_lock); if (ida_ret == -EAGAIN) goto retry; return -EIO; } if (index >= fsi->mount_opts.max) { ida_remove(&fsi->allocated_ptys, index); mutex_unlock(&allocated_ptys_lock); return -ENOSPC; } pty_count++; mutex_unlock(&allocated_ptys_lock); return index; } void devpts_kill_index(struct inode *ptmx_inode, int idx) { struct super_block *sb = pts_sb_from_inode(ptmx_inode); struct pts_fs_info *fsi = DEVPTS_SB(sb); mutex_lock(&allocated_ptys_lock); ida_remove(&fsi->allocated_ptys, idx); pty_count--; mutex_unlock(&allocated_ptys_lock); } /** * devpts_pty_new -- create a new inode in /dev/pts/ * @ptmx_inode: inode of the master * @device: major+minor of the node to be created * @index: used as a name of the node * @priv: what's given back by devpts_get_priv * * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill. */ struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index, void *priv) { struct dentry *dentry; struct super_block *sb = pts_sb_from_inode(ptmx_inode); struct inode *inode; struct dentry *root = sb->s_root; struct pts_fs_info *fsi = DEVPTS_SB(sb); struct pts_mount_opts *opts = &fsi->mount_opts; char s[12]; inode = new_inode(sb); if (!inode) return ERR_PTR(-ENOMEM); inode->i_ino = index + 3; inode->i_uid = opts->setuid ? opts->uid : current_fsuid(); inode->i_gid = opts->setgid ? opts->gid : current_fsgid(); inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; init_special_inode(inode, S_IFCHR|opts->mode, device); inode->i_private = priv; sprintf(s, "%d", index); mutex_lock(&root->d_inode->i_mutex); dentry = d_alloc_name(root, s); if (dentry) { d_add(dentry, inode); fsnotify_create(root->d_inode, dentry); } else { iput(inode); inode = ERR_PTR(-ENOMEM); } mutex_unlock(&root->d_inode->i_mutex); return inode; } /** * devpts_get_priv -- get private data for a slave * @pts_inode: inode of the slave * * Returns whatever was passed as priv in devpts_pty_new for a given inode. */ void *devpts_get_priv(struct inode *pts_inode) { struct dentry *dentry; void *priv = NULL; BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR)); /* Ensure dentry has not been deleted by devpts_pty_kill() */ dentry = d_find_alias(pts_inode); if (!dentry) return NULL; if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC) priv = pts_inode->i_private; dput(dentry); return priv; } /** * devpts_pty_kill -- remove inode form /dev/pts/ * @inode: inode of the slave to be removed * * This is an inverse operation of devpts_pty_new. */ void devpts_pty_kill(struct inode *inode) { struct super_block *sb = pts_sb_from_inode(inode); struct dentry *root = sb->s_root; struct dentry *dentry; BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR)); mutex_lock(&root->d_inode->i_mutex); dentry = d_find_alias(inode); drop_nlink(inode); d_delete(dentry); dput(dentry); /* d_alloc_name() in devpts_pty_new() */ dput(dentry); /* d_find_alias above */ mutex_unlock(&root->d_inode->i_mutex); } static int __init init_devpts_fs(void) { int err = register_filesystem(&devpts_fs_type); struct ctl_table_header *table; if (!err) { table = register_sysctl_table(pty_root_table); devpts_mnt = kern_mount(&devpts_fs_type); if (IS_ERR(devpts_mnt)) { err = PTR_ERR(devpts_mnt); unregister_filesystem(&devpts_fs_type); unregister_sysctl_table(table); } } return err; } module_init(init_devpts_fs)