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Linux/fs/proc/fd.c

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

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