1// SPDX-License-Identifier: GPL-2.0
  2#include <linux/sched/signal.h>
  3#include <linux/errno.h>
  4#include <linux/dcache.h>
  5#include <linux/path.h>
  6#include <linux/fdtable.h>
  7#include <linux/namei.h>
  8#include <linux/pid.h>
  9#include <linux/ptrace.h>
 10#include <linux/security.h>
 11#include <linux/file.h>
 12#include <linux/seq_file.h>
 13#include <linux/fs.h>
 14
 15#include <linux/proc_fs.h>
 16
 17#include "../mount.h"
 18#include "internal.h"
 19#include "fd.h"
 20
 21static int seq_show(struct seq_file *m, void *v)
 22{
 23	struct files_struct *files = NULL;
 24	int f_flags = 0, ret = -ENOENT;
 25	struct file *file = NULL;
 26	struct task_struct *task;
 27
 28	task = get_proc_task(m->private);
 29	if (!task)
 30		return -ENOENT;
 31
 32	task_lock(task);
 33	files = task->files;
 34	if (files) {
 35		unsigned int fd = proc_fd(m->private);
 36
 37		spin_lock(&files->file_lock);
 38		file = files_lookup_fd_locked(files, fd);
 39		if (file) {
 40			struct fdtable *fdt = files_fdtable(files);
 41
 42			f_flags = file->f_flags;
 43			if (close_on_exec(fd, fdt))
 44				f_flags |= O_CLOEXEC;
 45
 46			get_file(file);
 47			ret = 0;
 48		}
 49		spin_unlock(&files->file_lock);
 50	}
 51	task_unlock(task);
 52	put_task_struct(task);
 53
 54	if (ret)
 55		return ret;
 56
 57	seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\nino:\t%lu\n",
 58		   (long long)file->f_pos, f_flags,
 59		   real_mount(file->f_path.mnt)->mnt_id,
 60		   file_inode(file)->i_ino);
 61
 62	/* show_fd_locks() never deferences files so a stale value is safe */
 63	show_fd_locks(m, file, files);
 64	if (seq_has_overflowed(m))
 65		goto out;
 66
 67	if (file->f_op->show_fdinfo)
 68		file->f_op->show_fdinfo(m, file);
 69
 70out:
 71	fput(file);
 72	return 0;
 73}
 74
 75static int seq_fdinfo_open(struct inode *inode, struct file *file)
 76{
 77	bool allowed = false;
 78	struct task_struct *task = get_proc_task(inode);
 79
 80	if (!task)
 81		return -ESRCH;
 82
 83	allowed = ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
 84	put_task_struct(task);
 85
 86	if (!allowed)
 87		return -EACCES;
 88
 89	return single_open(file, seq_show, inode);
 90}
 91
 92static const struct file_operations proc_fdinfo_file_operations = {
 93	.open		= seq_fdinfo_open,
 94	.read		= seq_read,
 95	.llseek		= seq_lseek,
 96	.release	= single_release,
 97};
 98
 99static bool tid_fd_mode(struct task_struct *task, unsigned fd, fmode_t *mode)
100{
101	struct file *file;
102
103	rcu_read_lock();
104	file = task_lookup_fd_rcu(task, fd);
105	if (file)
106		*mode = file->f_mode;
107	rcu_read_unlock();
108	return !!file;
109}
110
111static void tid_fd_update_inode(struct task_struct *task, struct inode *inode,
112				fmode_t f_mode)
113{
114	task_dump_owner(task, 0, &inode->i_uid, &inode->i_gid);
115
116	if (S_ISLNK(inode->i_mode)) {
117		unsigned i_mode = S_IFLNK;
118		if (f_mode & FMODE_READ)
119			i_mode |= S_IRUSR | S_IXUSR;
120		if (f_mode & FMODE_WRITE)
121			i_mode |= S_IWUSR | S_IXUSR;
122		inode->i_mode = i_mode;
123	}
124	security_task_to_inode(task, inode);
125}
126
127static int tid_fd_revalidate(struct dentry *dentry, unsigned int flags)
128{
129	struct task_struct *task;
130	struct inode *inode;
131	unsigned int fd;
132
133	if (flags & LOOKUP_RCU)
134		return -ECHILD;
135
136	inode = d_inode(dentry);
137	task = get_proc_task(inode);
138	fd = proc_fd(inode);
139
140	if (task) {
141		fmode_t f_mode;
142		if (tid_fd_mode(task, fd, &f_mode)) {
143			tid_fd_update_inode(task, inode, f_mode);
144			put_task_struct(task);
145			return 1;
146		}
147		put_task_struct(task);
148	}
149	return 0;
150}
151
152static const struct dentry_operations tid_fd_dentry_operations = {
153	.d_revalidate	= tid_fd_revalidate,
154	.d_delete	= pid_delete_dentry,
155};
156
157static int proc_fd_link(struct dentry *dentry, struct path *path)
158{
159	struct task_struct *task;
160	int ret = -ENOENT;
161
162	task = get_proc_task(d_inode(dentry));
163	if (task) {
164		unsigned int fd = proc_fd(d_inode(dentry));
165		struct file *fd_file;
166
167		fd_file = fget_task(task, fd);
168		if (fd_file) {
169			*path = fd_file->f_path;
170			path_get(&fd_file->f_path);
171			ret = 0;
172			fput(fd_file);
173		}
174		put_task_struct(task);
175	}
176
177	return ret;
178}
179
180struct fd_data {
181	fmode_t mode;
182	unsigned fd;
183};
184
185static struct dentry *proc_fd_instantiate(struct dentry *dentry,
186	struct task_struct *task, const void *ptr)
187{
188	const struct fd_data *data = ptr;
189	struct proc_inode *ei;
190	struct inode *inode;
191
192	inode = proc_pid_make_inode(dentry->d_sb, task, S_IFLNK);
193	if (!inode)
194		return ERR_PTR(-ENOENT);
195
196	ei = PROC_I(inode);
197	ei->fd = data->fd;
198
199	inode->i_op = &proc_pid_link_inode_operations;
200	inode->i_size = 64;
201
202	ei->op.proc_get_link = proc_fd_link;
203	tid_fd_update_inode(task, inode, data->mode);
204
205	d_set_d_op(dentry, &tid_fd_dentry_operations);
206	return d_splice_alias(inode, dentry);
207}
208
209static struct dentry *proc_lookupfd_common(struct inode *dir,
210					   struct dentry *dentry,
211					   instantiate_t instantiate)
212{
213	struct task_struct *task = get_proc_task(dir);
214	struct fd_data data = {.fd = name_to_int(&dentry->d_name)};
215	struct dentry *result = ERR_PTR(-ENOENT);
216
217	if (!task)
218		goto out_no_task;
219	if (data.fd == ~0U)
220		goto out;
221	if (!tid_fd_mode(task, data.fd, &data.mode))
222		goto out;
223
224	result = instantiate(dentry, task, &data);
225out:
226	put_task_struct(task);
227out_no_task:
228	return result;
229}
230
231static int proc_readfd_common(struct file *file, struct dir_context *ctx,
232			      instantiate_t instantiate)
233{
234	struct task_struct *p = get_proc_task(file_inode(file));
235	unsigned int fd;
236
237	if (!p)
238		return -ENOENT;
239
240	if (!dir_emit_dots(file, ctx))
241		goto out;
242
243	rcu_read_lock();
244	for (fd = ctx->pos - 2;; fd++) {
245		struct file *f;
246		struct fd_data data;
247		char name[10 + 1];
248		unsigned int len;
249
250		f = task_lookup_next_fd_rcu(p, &fd);
251		ctx->pos = fd + 2LL;
252		if (!f)
253			break;
254		data.mode = f->f_mode;
255		rcu_read_unlock();
256		data.fd = fd;
257
258		len = snprintf(name, sizeof(name), "%u", fd);
259		if (!proc_fill_cache(file, ctx,
260				     name, len, instantiate, p,
261				     &data))
262			goto out;
263		cond_resched();
264		rcu_read_lock();
265	}
266	rcu_read_unlock();
267out:
268	put_task_struct(p);
269	return 0;
270}
271
272static int proc_readfd(struct file *file, struct dir_context *ctx)
273{
274	return proc_readfd_common(file, ctx, proc_fd_instantiate);
275}
276
277const struct file_operations proc_fd_operations = {
278	.read		= generic_read_dir,
279	.iterate_shared	= proc_readfd,
280	.llseek		= generic_file_llseek,
281};
282
283static struct dentry *proc_lookupfd(struct inode *dir, struct dentry *dentry,
284				    unsigned int flags)
285{
286	return proc_lookupfd_common(dir, dentry, proc_fd_instantiate);
287}
288
289/*
290 * /proc/pid/fd needs a special permission handler so that a process can still
291 * access /proc/self/fd after it has executed a setuid().
292 */
293int proc_fd_permission(struct user_namespace *mnt_userns,
294		       struct inode *inode, int mask)
295{
296	struct task_struct *p;
297	int rv;
298
299	rv = generic_permission(&init_user_ns, inode, mask);
300	if (rv == 0)
301		return rv;
302
303	rcu_read_lock();
304	p = pid_task(proc_pid(inode), PIDTYPE_PID);
305	if (p && same_thread_group(p, current))
306		rv = 0;
307	rcu_read_unlock();
308
309	return rv;
310}
311
312const struct inode_operations proc_fd_inode_operations = {
313	.lookup		= proc_lookupfd,
314	.permission	= proc_fd_permission,
315	.setattr	= proc_setattr,
316};
317
318static struct dentry *proc_fdinfo_instantiate(struct dentry *dentry,
319	struct task_struct *task, const void *ptr)
320{
321	const struct fd_data *data = ptr;
322	struct proc_inode *ei;
323	struct inode *inode;
324
325	inode = proc_pid_make_inode(dentry->d_sb, task, S_IFREG | S_IRUGO);
326	if (!inode)
327		return ERR_PTR(-ENOENT);
328
329	ei = PROC_I(inode);
330	ei->fd = data->fd;
331
332	inode->i_fop = &proc_fdinfo_file_operations;
333	tid_fd_update_inode(task, inode, 0);
334
335	d_set_d_op(dentry, &tid_fd_dentry_operations);
336	return d_splice_alias(inode, dentry);
337}
338
339static struct dentry *
340proc_lookupfdinfo(struct inode *dir, struct dentry *dentry, unsigned int flags)
341{
342	return proc_lookupfd_common(dir, dentry, proc_fdinfo_instantiate);
343}
344
345static int proc_readfdinfo(struct file *file, struct dir_context *ctx)
346{
347	return proc_readfd_common(file, ctx,
348				  proc_fdinfo_instantiate);
349}
350
351const struct inode_operations proc_fdinfo_inode_operations = {
352	.lookup		= proc_lookupfdinfo,
353	.setattr	= proc_setattr,
354};
355
356const struct file_operations proc_fdinfo_operations = {
357	.read		= generic_read_dir,
358	.iterate_shared	= proc_readfdinfo,
359	.llseek		= generic_file_llseek,
360};