xref: /openbmc/linux/fs/proc/fd.c (revision fce96cf0443083e37455eff8f78fd240c621dae3)
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  
21  static 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  
70  out:
71  	fput(file);
72  	return 0;
73  }
74  
75  static 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  
92  static 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  
99  static 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  
111  static 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  
127  static 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  
152  static const struct dentry_operations tid_fd_dentry_operations = {
153  	.d_revalidate	= tid_fd_revalidate,
154  	.d_delete	= pid_delete_dentry,
155  };
156  
157  static 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  
180  struct fd_data {
181  	fmode_t mode;
182  	unsigned fd;
183  };
184  
185  static 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  
209  static 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);
225  out:
226  	put_task_struct(task);
227  out_no_task:
228  	return result;
229  }
230  
231  static 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();
267  out:
268  	put_task_struct(p);
269  	return 0;
270  }
271  
272  static int proc_readfd(struct file *file, struct dir_context *ctx)
273  {
274  	return proc_readfd_common(file, ctx, proc_fd_instantiate);
275  }
276  
277  const struct file_operations proc_fd_operations = {
278  	.read		= generic_read_dir,
279  	.iterate_shared	= proc_readfd,
280  	.llseek		= generic_file_llseek,
281  };
282  
283  static 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   */
293  int 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  
312  const struct inode_operations proc_fd_inode_operations = {
313  	.lookup		= proc_lookupfd,
314  	.permission	= proc_fd_permission,
315  	.setattr	= proc_setattr,
316  };
317  
318  static 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  
339  static struct dentry *
340  proc_lookupfdinfo(struct inode *dir, struct dentry *dentry, unsigned int flags)
341  {
342  	return proc_lookupfd_common(dir, dentry, proc_fdinfo_instantiate);
343  }
344  
345  static int proc_readfdinfo(struct file *file, struct dir_context *ctx)
346  {
347  	return proc_readfd_common(file, ctx,
348  				  proc_fdinfo_instantiate);
349  }
350  
351  const struct inode_operations proc_fdinfo_inode_operations = {
352  	.lookup		= proc_lookupfdinfo,
353  	.setattr	= proc_setattr,
354  };
355  
356  const struct file_operations proc_fdinfo_operations = {
357  	.read		= generic_read_dir,
358  	.iterate_shared	= proc_readfdinfo,
359  	.llseek		= generic_file_llseek,
360  };
361