fs/pidfs.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/anon_inodes.h>
   3 #include <linux/file.h>
   4 #include <linux/fs.h>
   5 #include <linux/magic.h>
   6 #include <linux/mount.h>
   7 #include <linux/pid.h>
   8 #include <linux/pidfs.h>
   9 #include <linux/pid_namespace.h>
  10 #include <linux/poll.h>
  11 #include <linux/proc_fs.h>
  12 #include <linux/proc_ns.h>
  13 #include <linux/pseudo_fs.h>
  14 #include <linux/ptrace.h>
  15 #include <linux/seq_file.h>
  16 #include <uapi/linux/pidfd.h>
  17 #include <linux/ipc_namespace.h>
  18 #include <linux/time_namespace.h>
  19 #include <linux/utsname.h>
  20 #include <net/net_namespace.h>
  21
  22 #include "internal.h"
  23 #include "mount.h"
  24
  25 #ifdef CONFIG_PROC_FS
  26 /**
  27  * pidfd_show_fdinfo - print information about a pidfd
  28  * @m: proc fdinfo file
  29  * @f: file referencing a pidfd
  30  *
  31  * Pid:
  32  * This function will print the pid that a given pidfd refers to in the
  33  * pid namespace of the procfs instance.
  34  * If the pid namespace of the process is not a descendant of the pid
  35  * namespace of the procfs instance 0 will be shown as its pid. This is
  36  * similar to calling getppid() on a process whose parent is outside of
  37  * its pid namespace.
  38  *
  39  * NSpid:
  40  * If pid namespaces are supported then this function will also print
  41  * the pid of a given pidfd refers to for all descendant pid namespaces
  42  * starting from the current pid namespace of the instance, i.e. the
  43  * Pid field and the first entry in the NSpid field will be identical.
  44  * If the pid namespace of the process is not a descendant of the pid
  45  * namespace of the procfs instance 0 will be shown as its first NSpid
  46  * entry and no others will be shown.
  47  * Note that this differs from the Pid and NSpid fields in
  48  * /proc/<pid>/status where Pid and NSpid are always shown relative to
  49  * the  pid namespace of the procfs instance. The difference becomes
  50  * obvious when sending around a pidfd between pid namespaces from a
  51  * different branch of the tree, i.e. where no ancestral relation is
  52  * present between the pid namespaces:
  53  * - create two new pid namespaces ns1 and ns2 in the initial pid
  54  *   namespace (also take care to create new mount namespaces in the
  55  *   new pid namespace and mount procfs)
  56  * - create a process with a pidfd in ns1
  57  * - send pidfd from ns1 to ns2
  58  * - read /proc/self/fdinfo/<pidfd> and observe that both Pid and NSpid
  59  *   have exactly one entry, which is 0
  60  */
  61 static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
  62 {
  63         struct pid *pid = pidfd_pid(f);
  64         struct pid_namespace *ns;
  65         pid_t nr = -1;
  66
  67         if (likely(pid_has_task(pid, PIDTYPE_PID))) {
  68                 ns = proc_pid_ns(file_inode(m->file)->i_sb);
  69                 nr = pid_nr_ns(pid, ns);
  70         }
  71
  72         seq_put_decimal_ll(m, "Pid:\t", nr);
  73
  74 #ifdef CONFIG_PID_NS
  75         seq_put_decimal_ll(m, "\nNSpid:\t", nr);
  76         if (nr > 0) {
  77                 int i;
  78
  79                 /* If nr is non-zero it means that 'pid' is valid and that
  80                  * ns, i.e. the pid namespace associated with the procfs
  81                  * instance, is in the pid namespace hierarchy of pid.
  82                  * Start at one below the already printed level.
  83                  */
  84                 for (i = ns->level + 1; i <= pid->level; i++)
  85                         seq_put_decimal_ll(m, "\t", pid->numbers[i].nr);
  86         }
  87 #endif
  88         seq_putc(m, '\n');
  89 }
  90 #endif
  91
  92 /*
  93  * Poll support for process exit notification.
  94  */
  95 static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
  96 {
  97         struct pid *pid = pidfd_pid(file);
  98         bool thread = file->f_flags & PIDFD_THREAD;
  99         struct task_struct *task;
 100         __poll_t poll_flags = 0;
 101
 102         poll_wait(file, &pid->wait_pidfd, pts);
 103         /*
 104          * Depending on PIDFD_THREAD, inform pollers when the thread
 105          * or the whole thread-group exits.
 106          */
 107         guard(rcu)();
 108         task = pid_task(pid, PIDTYPE_PID);
 109         if (!task)
 110                 poll_flags = EPOLLIN | EPOLLRDNORM | EPOLLHUP;
 111         else if (task->exit_state && (thread || thread_group_empty(task)))
 112                 poll_flags = EPOLLIN | EPOLLRDNORM;
 113
 114         return poll_flags;
 115 }
 116
 117 static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 118 {
 119         struct task_struct *task __free(put_task) = NULL;
 120         struct nsproxy *nsp __free(put_nsproxy) = NULL;
 121         struct pid *pid = pidfd_pid(file);
 122         struct ns_common *ns_common = NULL;
 123
 124         if (arg)
 125                 return -EINVAL;
 126
 127         task = get_pid_task(pid, PIDTYPE_PID);
 128         if (!task)
 129                 return -ESRCH;
 130
 131         scoped_guard(task_lock, task) {
 132                 nsp = task->nsproxy;
 133                 if (nsp)
 134                         get_nsproxy(nsp);
 135         }
 136         if (!nsp)
 137                 return -ESRCH; /* just pretend it didn't exist */
 138
 139         /*
 140          * We're trying to open a file descriptor to the namespace so perform a
 141          * filesystem cred ptrace check. Also, we mirror nsfs behavior.
 142          */
 143         if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
 144                 return -EACCES;
 145
 146         switch (cmd) {
 147         /* Namespaces that hang of nsproxy. */
 148         case PIDFD_GET_CGROUP_NAMESPACE:
 149                 if (IS_ENABLED(CONFIG_CGROUPS)) {
 150                         get_cgroup_ns(nsp->cgroup_ns);
 151                         ns_common = to_ns_common(nsp->cgroup_ns);
 152                 }
 153                 break;
 154         case PIDFD_GET_IPC_NAMESPACE:
 155                 if (IS_ENABLED(CONFIG_IPC_NS)) {
 156                         get_ipc_ns(nsp->ipc_ns);
 157                         ns_common = to_ns_common(nsp->ipc_ns);
 158                 }
 159                 break;
 160         case PIDFD_GET_MNT_NAMESPACE:
 161                 get_mnt_ns(nsp->mnt_ns);
 162                 ns_common = to_ns_common(nsp->mnt_ns);
 163                 break;
 164         case PIDFD_GET_NET_NAMESPACE:
 165                 if (IS_ENABLED(CONFIG_NET_NS)) {
 166                         ns_common = to_ns_common(nsp->net_ns);
 167                         get_net_ns(ns_common);
 168                 }
 169                 break;
 170         case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE:
 171                 if (IS_ENABLED(CONFIG_PID_NS)) {
 172                         get_pid_ns(nsp->pid_ns_for_children);
 173                         ns_common = to_ns_common(nsp->pid_ns_for_children);
 174                 }
 175                 break;
 176         case PIDFD_GET_TIME_NAMESPACE:
 177                 if (IS_ENABLED(CONFIG_TIME_NS)) {
 178                         get_time_ns(nsp->time_ns);
 179                         ns_common = to_ns_common(nsp->time_ns);
 180                 }
 181                 break;
 182         case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE:
 183                 if (IS_ENABLED(CONFIG_TIME_NS)) {
 184                         get_time_ns(nsp->time_ns_for_children);
 185                         ns_common = to_ns_common(nsp->time_ns_for_children);
 186                 }
 187                 break;
 188         case PIDFD_GET_UTS_NAMESPACE:
 189                 if (IS_ENABLED(CONFIG_UTS_NS)) {
 190                         get_uts_ns(nsp->uts_ns);
 191                         ns_common = to_ns_common(nsp->uts_ns);
 192                 }
 193                 break;
 194         /* Namespaces that don't hang of nsproxy. */
 195         case PIDFD_GET_USER_NAMESPACE:
 196                 if (IS_ENABLED(CONFIG_USER_NS)) {
 197                         rcu_read_lock();
 198                         ns_common = to_ns_common(get_user_ns(task_cred_xxx(task, user_ns)));
 199                         rcu_read_unlock();
 200                 }
 201                 break;
 202         case PIDFD_GET_PID_NAMESPACE:
 203                 if (IS_ENABLED(CONFIG_PID_NS)) {
 204                         rcu_read_lock();
 205                         ns_common = to_ns_common( get_pid_ns(task_active_pid_ns(task)));
 206                         rcu_read_unlock();
 207                 }
 208                 break;
 209         default:
 210                 return -ENOIOCTLCMD;
 211         }
 212
 213         if (!ns_common)
 214                 return -EOPNOTSUPP;
 215
 216         /* open_namespace() unconditionally consumes the reference */
 217         return open_namespace(ns_common);
 218 }
 219
 220 static const struct file_operations pidfs_file_operations = {
 221         .poll           = pidfd_poll,
 222 #ifdef CONFIG_PROC_FS
 223         .show_fdinfo    = pidfd_show_fdinfo,
 224 #endif
 225         .unlocked_ioctl = pidfd_ioctl,
 226         .compat_ioctl   = compat_ptr_ioctl,
 227 };
 228
 229 struct pid *pidfd_pid(const struct file *file)
 230 {
 231         if (file->f_op != &pidfs_file_operations)
 232                 return ERR_PTR(-EBADF);
 233         return file_inode(file)->i_private;
 234 }
 235
 236 static struct vfsmount *pidfs_mnt __ro_after_init;
 237
 238 #if BITS_PER_LONG == 32
 239 /*
 240  * Provide a fallback mechanism for 32-bit systems so processes remain
 241  * reliably comparable by inode number even on those systems.
 242  */
 243 static DEFINE_IDA(pidfd_inum_ida);
 244
 245 static int pidfs_inum(struct pid *pid, unsigned long *ino)
 246 {
 247         int ret;
 248
 249         ret = ida_alloc_range(&pidfd_inum_ida, RESERVED_PIDS + 1,
 250                               UINT_MAX, GFP_ATOMIC);
 251         if (ret < 0)
 252                 return -ENOSPC;
 253
 254         *ino = ret;
 255         return 0;
 256 }
 257
 258 static inline void pidfs_free_inum(unsigned long ino)
 259 {
 260         if (ino > 0)
 261                 ida_free(&pidfd_inum_ida, ino);
 262 }
 263 #else
 264 static inline int pidfs_inum(struct pid *pid, unsigned long *ino)
 265 {
 266         *ino = pid->ino;
 267         return 0;
 268 }
 269 #define pidfs_free_inum(ino) ((void)(ino))
 270 #endif
 271
 272 /*
 273  * The vfs falls back to simple_setattr() if i_op->setattr() isn't
 274  * implemented. Let's reject it completely until we have a clean
 275  * permission concept for pidfds.
 276  */
 277 static int pidfs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 278                          struct iattr *attr)
 279 {
 280         return -EOPNOTSUPP;
 281 }
 282
 283
 284 /*
 285  * User space expects pidfs inodes to have no file type in st_mode.
 286  *
 287  * In particular, 'lsof' has this legacy logic:
 288  *
 289  *      type = s->st_mode & S_IFMT;
 290  *      switch (type) {
 291  *        ...
 292  *      case 0:
 293  *              if (!strcmp(p, "anon_inode"))
 294  *                      Lf->ntype = Ntype = N_ANON_INODE;
 295  *
 296  * to detect our old anon_inode logic.
 297  *
 298  * Rather than mess with our internal sane inode data, just fix it
 299  * up here in getattr() by masking off the format bits.
 300  */
 301 static int pidfs_getattr(struct mnt_idmap *idmap, const struct path *path,
 302                          struct kstat *stat, u32 request_mask,
 303                          unsigned int query_flags)
 304 {
 305         struct inode *inode = d_inode(path->dentry);
 306
 307         generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
 308         stat->mode &= ~S_IFMT;
 309         return 0;
 310 }
 311
 312 static const struct inode_operations pidfs_inode_operations = {
 313         .getattr = pidfs_getattr,
 314         .setattr = pidfs_setattr,
 315 };
 316
 317 static void pidfs_evict_inode(struct inode *inode)
 318 {
 319         struct pid *pid = inode->i_private;
 320
 321         clear_inode(inode);
 322         put_pid(pid);
 323         pidfs_free_inum(inode->i_ino);
 324 }
 325
 326 static const struct super_operations pidfs_sops = {
 327         .drop_inode     = generic_delete_inode,
 328         .evict_inode    = pidfs_evict_inode,
 329         .statfs         = simple_statfs,
 330 };
 331
 332 /*
 333  * 'lsof' has knowledge of out historical anon_inode use, and expects
 334  * the pidfs dentry name to start with 'anon_inode'.
 335  */
 336 static char *pidfs_dname(struct dentry *dentry, char *buffer, int buflen)
 337 {
 338         return dynamic_dname(buffer, buflen, "anon_inode:[pidfd]");
 339 }
 340
 341 static const struct dentry_operations pidfs_dentry_operations = {
 342         .d_delete       = always_delete_dentry,
 343         .d_dname        = pidfs_dname,
 344         .d_prune        = stashed_dentry_prune,
 345 };
 346
 347 static int pidfs_init_inode(struct inode *inode, void *data)
 348 {
 349         inode->i_private = data;
 350         inode->i_flags |= S_PRIVATE;
 351         inode->i_mode |= S_IRWXU;
 352         inode->i_op = &pidfs_inode_operations;
 353         inode->i_fop = &pidfs_file_operations;
 354         /*
 355          * Inode numbering for pidfs start at RESERVED_PIDS + 1. This
 356          * avoids collisions with the root inode which is 1 for pseudo
 357          * filesystems.
 358          */
 359         return pidfs_inum(data, &inode->i_ino);
 360 }
 361
 362 static void pidfs_put_data(void *data)
 363 {
 364         struct pid *pid = data;
 365         put_pid(pid);
 366 }
 367
 368 static const struct stashed_operations pidfs_stashed_ops = {
 369         .init_inode = pidfs_init_inode,
 370         .put_data = pidfs_put_data,
 371 };
 372
 373 static int pidfs_init_fs_context(struct fs_context *fc)
 374 {
 375         struct pseudo_fs_context *ctx;
 376
 377         ctx = init_pseudo(fc, PID_FS_MAGIC);
 378         if (!ctx)
 379                 return -ENOMEM;
 380
 381         ctx->ops = &pidfs_sops;
 382         ctx->dops = &pidfs_dentry_operations;
 383         fc->s_fs_info = (void *)&pidfs_stashed_ops;
 384         return 0;
 385 }
 386
 387 static struct file_system_type pidfs_type = {
 388         .name                   = "pidfs",
 389         .init_fs_context        = pidfs_init_fs_context,
 390         .kill_sb                = kill_anon_super,
 391 };
 392
 393 struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
 394 {
 395
 396         struct file *pidfd_file;
 397         struct path path;
 398         int ret;
 399
 400         ret = path_from_stashed(&pid->stashed, pidfs_mnt, get_pid(pid), &path);
 401         if (ret < 0)
 402                 return ERR_PTR(ret);
 403
 404         pidfd_file = dentry_open(&path, flags, current_cred());
 405         path_put(&path);
 406         return pidfd_file;
 407 }
 408
 409 void __init pidfs_init(void)
 410 {
 411         pidfs_mnt = kern_mount(&pidfs_type);
 412         if (IS_ERR(pidfs_mnt))
 413                 panic("Failed to mount pidfs pseudo filesystem");
 414 }