root.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 *  linux/fs/proc/root.c
  4 *
  5 *  Copyright (C) 1991, 1992 Linus Torvalds
  6 *
  7 *  proc root directory handling functions
  8 */
  9#include <linux/errno.h>
 10#include <linux/time.h>
 11#include <linux/proc_fs.h>
 12#include <linux/stat.h>
 13#include <linux/init.h>
 14#include <linux/sched.h>
 15#include <linux/sched/stat.h>
 16#include <linux/module.h>
 17#include <linux/bitops.h>
 18#include <linux/user_namespace.h>
 19#include <linux/fs_context.h>
 20#include <linux/mount.h>
 21#include <linux/pid_namespace.h>
 22#include <linux/fs_parser.h>
 23#include <linux/cred.h>
 24#include <linux/magic.h>
 25#include <linux/slab.h>
 26
 27#include "internal.h"
 28
 29struct proc_fs_context {
 30	struct pid_namespace	*pid_ns;
 31	unsigned int		mask;
 32	enum proc_hidepid	hidepid;
 33	int			gid;
 34	enum proc_pidonly	pidonly;
 35};
 36
 37enum proc_param {
 38	Opt_gid,
 39	Opt_hidepid,
 40	Opt_subset,
 41	Opt_pidns,
 42};
 43
 44static const struct fs_parameter_spec proc_fs_parameters[] = {
 45	fsparam_u32("gid",		Opt_gid),
 46	fsparam_string("hidepid",	Opt_hidepid),
 47	fsparam_string("subset",	Opt_subset),
 48	fsparam_file_or_string("pidns",	Opt_pidns),
 49	{}
 50};
 51
 52static inline int valid_hidepid(unsigned int value)
 53{
 54	return (value == HIDEPID_OFF ||
 55		value == HIDEPID_NO_ACCESS ||
 56		value == HIDEPID_INVISIBLE ||
 57		value == HIDEPID_NOT_PTRACEABLE);
 58}
 59
 60static int proc_parse_hidepid_param(struct fs_context *fc, struct fs_parameter *param)
 61{
 62	struct proc_fs_context *ctx = fc->fs_private;
 63	struct fs_parameter_spec hidepid_u32_spec = fsparam_u32("hidepid", Opt_hidepid);
 64	struct fs_parse_result result;
 65	int base = (unsigned long)hidepid_u32_spec.data;
 66
 67	if (param->type != fs_value_is_string)
 68		return invalf(fc, "proc: unexpected type of hidepid value\n");
 69
 70	if (!kstrtouint(param->string, base, &result.uint_32)) {
 71		if (!valid_hidepid(result.uint_32))
 72			return invalf(fc, "proc: unknown value of hidepid - %s\n", param->string);
 73		ctx->hidepid = result.uint_32;
 74		return 0;
 75	}
 76
 77	if (!strcmp(param->string, "off"))
 78		ctx->hidepid = HIDEPID_OFF;
 79	else if (!strcmp(param->string, "noaccess"))
 80		ctx->hidepid = HIDEPID_NO_ACCESS;
 81	else if (!strcmp(param->string, "invisible"))
 82		ctx->hidepid = HIDEPID_INVISIBLE;
 83	else if (!strcmp(param->string, "ptraceable"))
 84		ctx->hidepid = HIDEPID_NOT_PTRACEABLE;
 85	else
 86		return invalf(fc, "proc: unknown value of hidepid - %s\n", param->string);
 87
 88	return 0;
 89}
 90
 91static int proc_parse_subset_param(struct fs_context *fc, char *value)
 92{
 93	struct proc_fs_context *ctx = fc->fs_private;
 94
 95	while (value) {
 96		char *ptr = strchr(value, ',');
 97
 98		if (ptr != NULL)
 99			*ptr++ = '\0';
100
101		if (*value != '\0') {
102			if (!strcmp(value, "pid")) {
103				ctx->pidonly = PROC_PIDONLY_ON;
104			} else {
105				return invalf(fc, "proc: unsupported subset option - %s\n", value);
106			}
107		}
108		value = ptr;
109	}
110
111	return 0;
112}
113
114#ifdef CONFIG_PID_NS
115static int proc_parse_pidns_param(struct fs_context *fc,
116				  struct fs_parameter *param,
117				  struct fs_parse_result *result)
118{
119	struct proc_fs_context *ctx = fc->fs_private;
120	struct pid_namespace *target, *active = task_active_pid_ns(current);
121	struct ns_common *ns;
122	struct file *ns_filp __free(fput) = NULL;
123
124	switch (param->type) {
125	case fs_value_is_file:
126		/* came through fsconfig, steal the file reference */
127		ns_filp = no_free_ptr(param->file);
128		break;
129	case fs_value_is_string:
130		ns_filp = filp_open(param->string, O_RDONLY, 0);
131		break;
132	default:
133		WARN_ON_ONCE(true);
134		break;
135	}
136	if (!ns_filp)
137		ns_filp = ERR_PTR(-EBADF);
138	if (IS_ERR(ns_filp)) {
139		errorfc(fc, "could not get file from pidns argument");
140		return PTR_ERR(ns_filp);
141	}
142
143	if (!proc_ns_file(ns_filp))
144		return invalfc(fc, "pidns argument is not an nsfs file");
145	ns = get_proc_ns(file_inode(ns_filp));
146	if (ns->ns_type != CLONE_NEWPID)
147		return invalfc(fc, "pidns argument is not a pidns file");
148	target = container_of(ns, struct pid_namespace, ns);
149
150	/*
151	 * pidns= is shorthand for joining the pidns to get a fsopen fd, so the
152	 * permission model should be the same as pidns_install().
153	 */
154	if (!ns_capable(target->user_ns, CAP_SYS_ADMIN)) {
155		errorfc(fc, "insufficient permissions to set pidns");
156		return -EPERM;
157	}
158	if (!pidns_is_ancestor(target, active))
159		return invalfc(fc, "cannot set pidns to non-descendant pidns");
160
161	put_pid_ns(ctx->pid_ns);
162	ctx->pid_ns = get_pid_ns(target);
163	put_user_ns(fc->user_ns);
164	fc->user_ns = get_user_ns(ctx->pid_ns->user_ns);
165	return 0;
166}
167#endif /* CONFIG_PID_NS */
168
169static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
170{
171	struct proc_fs_context *ctx = fc->fs_private;
172	struct fs_parse_result result;
173	int opt, err;
174
175	opt = fs_parse(fc, proc_fs_parameters, param, &result);
176	if (opt < 0)
177		return opt;
178
179	switch (opt) {
180	case Opt_gid:
181		ctx->gid = result.uint_32;
182		break;
183
184	case Opt_hidepid:
185		err = proc_parse_hidepid_param(fc, param);
186		if (err)
187			return err;
188		break;
189
190	case Opt_subset:
191		err = proc_parse_subset_param(fc, param->string);
192		if (err)
193			return err;
194		break;
195
196	case Opt_pidns:
197#ifdef CONFIG_PID_NS
198		/*
199		 * We would have to RCU-protect every proc_pid_ns() or
200		 * proc_sb_info() access if we allowed this to be reconfigured
201		 * for an existing procfs instance. Luckily, procfs instances
202		 * are cheap to create, and mount-beneath would let you
203		 * atomically replace an instance even with overmounts.
204		 */
205		if (fc->purpose == FS_CONTEXT_FOR_RECONFIGURE) {
206			errorfc(fc, "cannot reconfigure pidns for existing procfs");
207			return -EBUSY;
208		}
209		err = proc_parse_pidns_param(fc, param, &result);
210		if (err)
211			return err;
212		break;
213#else
214		errorfc(fc, "pidns mount flag not supported on this system");
215		return -EOPNOTSUPP;
216#endif
217
218	default:
219		return -EINVAL;
220	}
221
222	ctx->mask |= 1 << opt;
223	return 0;
224}
225
226static void proc_apply_options(struct proc_fs_info *fs_info,
227			       struct fs_context *fc,
228			       struct user_namespace *user_ns)
229{
230	struct proc_fs_context *ctx = fc->fs_private;
231
232	if (ctx->mask & (1 << Opt_gid))
233		fs_info->pid_gid = make_kgid(user_ns, ctx->gid);
234	if (ctx->mask & (1 << Opt_hidepid))
235		fs_info->hide_pid = ctx->hidepid;
236	if (ctx->mask & (1 << Opt_subset))
237		fs_info->pidonly = ctx->pidonly;
238	if (ctx->mask & (1 << Opt_pidns) &&
239	    !WARN_ON_ONCE(fc->purpose == FS_CONTEXT_FOR_RECONFIGURE)) {
240		put_pid_ns(fs_info->pid_ns);
241		fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
242	}
243}
244
245static int proc_fill_super(struct super_block *s, struct fs_context *fc)
246{
247	struct proc_fs_context *ctx = fc->fs_private;
248	struct inode *root_inode;
249	struct proc_fs_info *fs_info;
250	int ret;
251
252	fs_info = kzalloc(sizeof(*fs_info), GFP_KERNEL);
253	if (!fs_info)
254		return -ENOMEM;
255
256	fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
257	proc_apply_options(fs_info, fc, current_user_ns());
258
259	/* User space would break if executables or devices appear on proc */
260	s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV;
261	s->s_flags |= SB_NODIRATIME | SB_NOSUID | SB_NOEXEC;
262	s->s_blocksize = 1024;
263	s->s_blocksize_bits = 10;
264	s->s_magic = PROC_SUPER_MAGIC;
265	s->s_op = &proc_sops;
266	s->s_time_gran = 1;
267	s->s_fs_info = fs_info;
268
269	/*
270	 * procfs isn't actually a stacking filesystem; however, there is
271	 * too much magic going on inside it to permit stacking things on
272	 * top of it
273	 */
274	s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
275
276	/* procfs dentries and inodes don't require IO to create */
277	s->s_shrink->seeks = 0;
278
279	pde_get(&proc_root);
280	root_inode = proc_get_inode(s, &proc_root);
281	if (!root_inode) {
282		pr_err("proc_fill_super: get root inode failed\n");
283		return -ENOMEM;
284	}
285
286	s->s_root = d_make_root(root_inode);
287	if (!s->s_root) {
288		pr_err("proc_fill_super: allocate dentry failed\n");
289		return -ENOMEM;
290	}
291
292	ret = proc_setup_self(s);
293	if (ret) {
294		return ret;
295	}
296	return proc_setup_thread_self(s);
297}
298
299static int proc_reconfigure(struct fs_context *fc)
300{
301	struct super_block *sb = fc->root->d_sb;
302	struct proc_fs_info *fs_info = proc_sb_info(sb);
303
304	sync_filesystem(sb);
305
306	proc_apply_options(fs_info, fc, current_user_ns());
307	return 0;
308}
309
310static int proc_get_tree(struct fs_context *fc)
311{
312	return get_tree_nodev(fc, proc_fill_super);
313}
314
315static void proc_fs_context_free(struct fs_context *fc)
316{
317	struct proc_fs_context *ctx = fc->fs_private;
318
319	put_pid_ns(ctx->pid_ns);
320	kfree(ctx);
321}
322
323static const struct fs_context_operations proc_fs_context_ops = {
324	.free		= proc_fs_context_free,
325	.parse_param	= proc_parse_param,
326	.get_tree	= proc_get_tree,
327	.reconfigure	= proc_reconfigure,
328};
329
330static int proc_init_fs_context(struct fs_context *fc)
331{
332	struct proc_fs_context *ctx;
333
334	ctx = kzalloc(sizeof(struct proc_fs_context), GFP_KERNEL);
335	if (!ctx)
336		return -ENOMEM;
337
338	ctx->pid_ns = get_pid_ns(task_active_pid_ns(current));
339	put_user_ns(fc->user_ns);
340	fc->user_ns = get_user_ns(ctx->pid_ns->user_ns);
341	fc->fs_private = ctx;
342	fc->ops = &proc_fs_context_ops;
343	return 0;
344}
345
346static void proc_kill_sb(struct super_block *sb)
347{
348	struct proc_fs_info *fs_info = proc_sb_info(sb);
349
350	kill_anon_super(sb);
351	if (fs_info) {
352		put_pid_ns(fs_info->pid_ns);
353		kfree_rcu(fs_info, rcu);
354	}
355}
356
357static struct file_system_type proc_fs_type = {
358	.name			= "proc",
359	.init_fs_context	= proc_init_fs_context,
360	.parameters		= proc_fs_parameters,
361	.kill_sb		= proc_kill_sb,
362	.fs_flags		= FS_USERNS_MOUNT | FS_DISALLOW_NOTIFY_PERM,
363};
364
365void __init proc_root_init(void)
366{
367	proc_init_kmemcache();
368	set_proc_pid_nlink();
369	proc_self_init();
370	proc_thread_self_init();
371	proc_symlink("mounts", NULL, "self/mounts");
372
373	proc_net_init();
374	proc_mkdir("fs", NULL);
375	proc_mkdir("driver", NULL);
376	proc_create_mount_point("fs/nfsd"); /* somewhere for the nfsd filesystem to be mounted */
377#if defined(CONFIG_SUN_OPENPROMFS) || defined(CONFIG_SUN_OPENPROMFS_MODULE)
378	/* just give it a mountpoint */
379	proc_create_mount_point("openprom");
380#endif
381	proc_tty_init();
382	proc_mkdir("bus", NULL);
383	proc_sys_init();
384
385	/*
386	 * Last things last. It is not like userspace processes eager
387	 * to open /proc files exist at this point but register last
388	 * anyway.
389	 */
390	register_filesystem(&proc_fs_type);
391}
392
393static int proc_root_getattr(struct mnt_idmap *idmap,
394			     const struct path *path, struct kstat *stat,
395			     u32 request_mask, unsigned int query_flags)
396{
397	generic_fillattr(&nop_mnt_idmap, request_mask, d_inode(path->dentry),
398			 stat);
399	stat->nlink = proc_root.nlink + nr_processes();
400	return 0;
401}
402
403static struct dentry *proc_root_lookup(struct inode * dir, struct dentry * dentry, unsigned int flags)
404{
405	if (!proc_pid_lookup(dentry, flags))
406		return NULL;
407
408	return proc_lookup(dir, dentry, flags);
409}
410
411static int proc_root_readdir(struct file *file, struct dir_context *ctx)
412{
413	if (ctx->pos < FIRST_PROCESS_ENTRY) {
414		int error = proc_readdir(file, ctx);
415		if (unlikely(error <= 0))
416			return error;
417		ctx->pos = FIRST_PROCESS_ENTRY;
418	}
419
420	return proc_pid_readdir(file, ctx);
421}
422
423/*
424 * The root /proc directory is special, as it has the
425 * <pid> directories. Thus we don't use the generic
426 * directory handling functions for that..
427 */
428static const struct file_operations proc_root_operations = {
429	.read		 = generic_read_dir,
430	.iterate_shared	 = proc_root_readdir,
431	.llseek		= generic_file_llseek,
432};
433
434/*
435 * proc root can do almost nothing..
436 */
437static const struct inode_operations proc_root_inode_operations = {
438	.lookup		= proc_root_lookup,
439	.getattr	= proc_root_getattr,
440};
441
442/*
443 * This is the root "inode" in the /proc tree..
444 */
445struct proc_dir_entry proc_root = {
446	.low_ino	= PROCFS_ROOT_INO,
447	.namelen	= 5,
448	.mode		= S_IFDIR | S_IRUGO | S_IXUGO,
449	.nlink		= 2,
450	.refcnt		= REFCOUNT_INIT(1),
451	.proc_iops	= &proc_root_inode_operations,
452	.proc_dir_ops	= &proc_root_operations,
453	.parent		= &proc_root,
454	.subdir		= RB_ROOT,
455	.name		= "/proc",
456};