1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/anon_inodes.h> 3 #include <linux/exportfs.h> 4 #include <linux/file.h> 5 #include <linux/fs.h> 6 #include <linux/cgroup.h> 7 #include <linux/magic.h> 8 #include <linux/mount.h> 9 #include <linux/pid.h> 10 #include <linux/pidfs.h> 11 #include <linux/pid_namespace.h> 12 #include <linux/poll.h> 13 #include <linux/proc_fs.h> 14 #include <linux/proc_ns.h> 15 #include <linux/pseudo_fs.h> 16 #include <linux/ptrace.h> 17 #include <linux/seq_file.h> 18 #include <uapi/linux/pidfd.h> 19 #include <linux/ipc_namespace.h> 20 #include <linux/time_namespace.h> 21 #include <linux/utsname.h> 22 #include <net/net_namespace.h> 23 #include <linux/coredump.h> 24 #include <linux/xattr.h> 25 26 #include "internal.h" 27 #include "mount.h" 28 29 #define PIDFS_PID_DEAD ERR_PTR(-ESRCH) 30 31 static struct kmem_cache *pidfs_attr_cachep __ro_after_init; 32 static struct kmem_cache *pidfs_xattr_cachep __ro_after_init; 33 34 static struct path pidfs_root_path = {}; 35 36 void pidfs_get_root(struct path *path) 37 { 38 *path = pidfs_root_path; 39 path_get(path); 40 } 41 42 /* 43 * Stashes information that userspace needs to access even after the 44 * process has been reaped. 45 */ 46 struct pidfs_exit_info { 47 __u64 cgroupid; 48 __s32 exit_code; 49 __u32 coredump_mask; 50 }; 51 52 struct pidfs_attr { 53 struct simple_xattrs *xattrs; 54 struct pidfs_exit_info __pei; 55 struct pidfs_exit_info *exit_info; 56 }; 57 58 static struct rb_root pidfs_ino_tree = RB_ROOT; 59 60 #if BITS_PER_LONG == 32 61 static inline unsigned long pidfs_ino(u64 ino) 62 { 63 return lower_32_bits(ino); 64 } 65 66 /* On 32 bit the generation number are the upper 32 bits. */ 67 static inline u32 pidfs_gen(u64 ino) 68 { 69 return upper_32_bits(ino); 70 } 71 72 #else 73 74 /* On 64 bit simply return ino. */ 75 static inline unsigned long pidfs_ino(u64 ino) 76 { 77 return ino; 78 } 79 80 /* On 64 bit the generation number is 0. */ 81 static inline u32 pidfs_gen(u64 ino) 82 { 83 return 0; 84 } 85 #endif 86 87 static int pidfs_ino_cmp(struct rb_node *a, const struct rb_node *b) 88 { 89 struct pid *pid_a = rb_entry(a, struct pid, pidfs_node); 90 struct pid *pid_b = rb_entry(b, struct pid, pidfs_node); 91 u64 pid_ino_a = pid_a->ino; 92 u64 pid_ino_b = pid_b->ino; 93 94 if (pid_ino_a < pid_ino_b) 95 return -1; 96 if (pid_ino_a > pid_ino_b) 97 return 1; 98 return 0; 99 } 100 101 void pidfs_add_pid(struct pid *pid) 102 { 103 static u64 pidfs_ino_nr = 2; 104 105 /* 106 * On 64 bit nothing special happens. The 64bit number assigned 107 * to struct pid is the inode number. 108 * 109 * On 32 bit the 64 bit number assigned to struct pid is split 110 * into two 32 bit numbers. The lower 32 bits are used as the 111 * inode number and the upper 32 bits are used as the inode 112 * generation number. 113 * 114 * On 32 bit pidfs_ino() will return the lower 32 bit. When 115 * pidfs_ino() returns zero a wrap around happened. When a 116 * wraparound happens the 64 bit number will be incremented by 2 117 * so inode numbering starts at 2 again. 118 * 119 * On 64 bit comparing two pidfds is as simple as comparing 120 * inode numbers. 121 * 122 * When a wraparound happens on 32 bit multiple pidfds with the 123 * same inode number are likely to exist (This isn't a problem 124 * since before pidfs pidfds used the anonymous inode meaning 125 * all pidfds had the same inode number.). Userspace can 126 * reconstruct the 64 bit identifier by retrieving both the 127 * inode number and the inode generation number to compare or 128 * use file handles. 129 */ 130 if (pidfs_ino(pidfs_ino_nr) == 0) 131 pidfs_ino_nr += 2; 132 133 pid->ino = pidfs_ino_nr; 134 pid->stashed = NULL; 135 pid->attr = NULL; 136 pidfs_ino_nr++; 137 138 write_seqcount_begin(&pidmap_lock_seq); 139 rb_find_add_rcu(&pid->pidfs_node, &pidfs_ino_tree, pidfs_ino_cmp); 140 write_seqcount_end(&pidmap_lock_seq); 141 } 142 143 void pidfs_remove_pid(struct pid *pid) 144 { 145 write_seqcount_begin(&pidmap_lock_seq); 146 rb_erase(&pid->pidfs_node, &pidfs_ino_tree); 147 write_seqcount_end(&pidmap_lock_seq); 148 } 149 150 void pidfs_free_pid(struct pid *pid) 151 { 152 struct pidfs_attr *attr __free(kfree) = no_free_ptr(pid->attr); 153 struct simple_xattrs *xattrs __free(kfree) = NULL; 154 155 /* 156 * Any dentry must've been wiped from the pid by now. 157 * Otherwise there's a reference count bug. 158 */ 159 VFS_WARN_ON_ONCE(pid->stashed); 160 161 /* 162 * This if an error occurred during e.g., task creation that 163 * causes us to never go through the exit path. 164 */ 165 if (unlikely(!attr)) 166 return; 167 168 /* This never had a pidfd created. */ 169 if (IS_ERR(attr)) 170 return; 171 172 xattrs = no_free_ptr(attr->xattrs); 173 if (xattrs) 174 simple_xattrs_free(xattrs, NULL); 175 } 176 177 #ifdef CONFIG_PROC_FS 178 /** 179 * pidfd_show_fdinfo - print information about a pidfd 180 * @m: proc fdinfo file 181 * @f: file referencing a pidfd 182 * 183 * Pid: 184 * This function will print the pid that a given pidfd refers to in the 185 * pid namespace of the procfs instance. 186 * If the pid namespace of the process is not a descendant of the pid 187 * namespace of the procfs instance 0 will be shown as its pid. This is 188 * similar to calling getppid() on a process whose parent is outside of 189 * its pid namespace. 190 * 191 * NSpid: 192 * If pid namespaces are supported then this function will also print 193 * the pid of a given pidfd refers to for all descendant pid namespaces 194 * starting from the current pid namespace of the instance, i.e. the 195 * Pid field and the first entry in the NSpid field will be identical. 196 * If the pid namespace of the process is not a descendant of the pid 197 * namespace of the procfs instance 0 will be shown as its first NSpid 198 * entry and no others will be shown. 199 * Note that this differs from the Pid and NSpid fields in 200 * /proc/<pid>/status where Pid and NSpid are always shown relative to 201 * the pid namespace of the procfs instance. The difference becomes 202 * obvious when sending around a pidfd between pid namespaces from a 203 * different branch of the tree, i.e. where no ancestral relation is 204 * present between the pid namespaces: 205 * - create two new pid namespaces ns1 and ns2 in the initial pid 206 * namespace (also take care to create new mount namespaces in the 207 * new pid namespace and mount procfs) 208 * - create a process with a pidfd in ns1 209 * - send pidfd from ns1 to ns2 210 * - read /proc/self/fdinfo/<pidfd> and observe that both Pid and NSpid 211 * have exactly one entry, which is 0 212 */ 213 static void pidfd_show_fdinfo(struct seq_file *m, struct file *f) 214 { 215 struct pid *pid = pidfd_pid(f); 216 struct pid_namespace *ns; 217 pid_t nr = -1; 218 219 if (likely(pid_has_task(pid, PIDTYPE_PID))) { 220 ns = proc_pid_ns(file_inode(m->file)->i_sb); 221 nr = pid_nr_ns(pid, ns); 222 } 223 224 seq_put_decimal_ll(m, "Pid:\t", nr); 225 226 #ifdef CONFIG_PID_NS 227 seq_put_decimal_ll(m, "\nNSpid:\t", nr); 228 if (nr > 0) { 229 int i; 230 231 /* If nr is non-zero it means that 'pid' is valid and that 232 * ns, i.e. the pid namespace associated with the procfs 233 * instance, is in the pid namespace hierarchy of pid. 234 * Start at one below the already printed level. 235 */ 236 for (i = ns->level + 1; i <= pid->level; i++) 237 seq_put_decimal_ll(m, "\t", pid->numbers[i].nr); 238 } 239 #endif 240 seq_putc(m, '\n'); 241 } 242 #endif 243 244 /* 245 * Poll support for process exit notification. 246 */ 247 static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts) 248 { 249 struct pid *pid = pidfd_pid(file); 250 struct task_struct *task; 251 __poll_t poll_flags = 0; 252 253 poll_wait(file, &pid->wait_pidfd, pts); 254 /* 255 * Don't wake waiters if the thread-group leader exited 256 * prematurely. They either get notified when the last subthread 257 * exits or not at all if one of the remaining subthreads execs 258 * and assumes the struct pid of the old thread-group leader. 259 */ 260 guard(rcu)(); 261 task = pid_task(pid, PIDTYPE_PID); 262 if (!task) 263 poll_flags = EPOLLIN | EPOLLRDNORM | EPOLLHUP; 264 else if (task->exit_state && !delay_group_leader(task)) 265 poll_flags = EPOLLIN | EPOLLRDNORM; 266 267 return poll_flags; 268 } 269 270 static inline bool pid_in_current_pidns(const struct pid *pid) 271 { 272 const struct pid_namespace *ns = task_active_pid_ns(current); 273 274 if (ns->level <= pid->level) 275 return pid->numbers[ns->level].ns == ns; 276 277 return false; 278 } 279 280 static __u32 pidfs_coredump_mask(unsigned long mm_flags) 281 { 282 switch (__get_dumpable(mm_flags)) { 283 case SUID_DUMP_USER: 284 return PIDFD_COREDUMP_USER; 285 case SUID_DUMP_ROOT: 286 return PIDFD_COREDUMP_ROOT; 287 case SUID_DUMP_DISABLE: 288 return PIDFD_COREDUMP_SKIP; 289 default: 290 WARN_ON_ONCE(true); 291 } 292 293 return 0; 294 } 295 296 static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg) 297 { 298 struct pidfd_info __user *uinfo = (struct pidfd_info __user *)arg; 299 struct task_struct *task __free(put_task) = NULL; 300 struct pid *pid = pidfd_pid(file); 301 size_t usize = _IOC_SIZE(cmd); 302 struct pidfd_info kinfo = {}; 303 struct pidfs_exit_info *exit_info; 304 struct user_namespace *user_ns; 305 struct pidfs_attr *attr; 306 const struct cred *c; 307 __u64 mask; 308 309 if (!uinfo) 310 return -EINVAL; 311 if (usize < PIDFD_INFO_SIZE_VER0) 312 return -EINVAL; /* First version, no smaller struct possible */ 313 314 if (copy_from_user(&mask, &uinfo->mask, sizeof(mask))) 315 return -EFAULT; 316 317 /* 318 * Restrict information retrieval to tasks within the caller's pid 319 * namespace hierarchy. 320 */ 321 if (!pid_in_current_pidns(pid)) 322 return -ESRCH; 323 324 attr = READ_ONCE(pid->attr); 325 if (mask & PIDFD_INFO_EXIT) { 326 exit_info = READ_ONCE(attr->exit_info); 327 if (exit_info) { 328 kinfo.mask |= PIDFD_INFO_EXIT; 329 #ifdef CONFIG_CGROUPS 330 kinfo.cgroupid = exit_info->cgroupid; 331 kinfo.mask |= PIDFD_INFO_CGROUPID; 332 #endif 333 kinfo.exit_code = exit_info->exit_code; 334 } 335 } 336 337 if (mask & PIDFD_INFO_COREDUMP) { 338 kinfo.mask |= PIDFD_INFO_COREDUMP; 339 kinfo.coredump_mask = READ_ONCE(attr->__pei.coredump_mask); 340 } 341 342 task = get_pid_task(pid, PIDTYPE_PID); 343 if (!task) { 344 /* 345 * If the task has already been reaped, only exit 346 * information is available 347 */ 348 if (!(mask & PIDFD_INFO_EXIT)) 349 return -ESRCH; 350 351 goto copy_out; 352 } 353 354 c = get_task_cred(task); 355 if (!c) 356 return -ESRCH; 357 358 if ((kinfo.mask & PIDFD_INFO_COREDUMP) && !(kinfo.coredump_mask)) { 359 task_lock(task); 360 if (task->mm) { 361 unsigned long flags = __mm_flags_get_dumpable(task->mm); 362 363 kinfo.coredump_mask = pidfs_coredump_mask(flags); 364 } 365 task_unlock(task); 366 } 367 368 /* Unconditionally return identifiers and credentials, the rest only on request */ 369 370 user_ns = current_user_ns(); 371 kinfo.ruid = from_kuid_munged(user_ns, c->uid); 372 kinfo.rgid = from_kgid_munged(user_ns, c->gid); 373 kinfo.euid = from_kuid_munged(user_ns, c->euid); 374 kinfo.egid = from_kgid_munged(user_ns, c->egid); 375 kinfo.suid = from_kuid_munged(user_ns, c->suid); 376 kinfo.sgid = from_kgid_munged(user_ns, c->sgid); 377 kinfo.fsuid = from_kuid_munged(user_ns, c->fsuid); 378 kinfo.fsgid = from_kgid_munged(user_ns, c->fsgid); 379 kinfo.mask |= PIDFD_INFO_CREDS; 380 put_cred(c); 381 382 #ifdef CONFIG_CGROUPS 383 if (!kinfo.cgroupid) { 384 struct cgroup *cgrp; 385 386 rcu_read_lock(); 387 cgrp = task_dfl_cgroup(task); 388 kinfo.cgroupid = cgroup_id(cgrp); 389 kinfo.mask |= PIDFD_INFO_CGROUPID; 390 rcu_read_unlock(); 391 } 392 #endif 393 394 /* 395 * Copy pid/tgid last, to reduce the chances the information might be 396 * stale. Note that it is not possible to ensure it will be valid as the 397 * task might return as soon as the copy_to_user finishes, but that's ok 398 * and userspace expects that might happen and can act accordingly, so 399 * this is just best-effort. What we can do however is checking that all 400 * the fields are set correctly, or return ESRCH to avoid providing 401 * incomplete information. */ 402 403 kinfo.ppid = task_ppid_nr_ns(task, NULL); 404 kinfo.tgid = task_tgid_vnr(task); 405 kinfo.pid = task_pid_vnr(task); 406 kinfo.mask |= PIDFD_INFO_PID; 407 408 if (kinfo.pid == 0 || kinfo.tgid == 0) 409 return -ESRCH; 410 411 copy_out: 412 /* 413 * If userspace and the kernel have the same struct size it can just 414 * be copied. If userspace provides an older struct, only the bits that 415 * userspace knows about will be copied. If userspace provides a new 416 * struct, only the bits that the kernel knows about will be copied. 417 */ 418 return copy_struct_to_user(uinfo, usize, &kinfo, sizeof(kinfo), NULL); 419 } 420 421 static bool pidfs_ioctl_valid(unsigned int cmd) 422 { 423 switch (cmd) { 424 case FS_IOC_GETVERSION: 425 case PIDFD_GET_CGROUP_NAMESPACE: 426 case PIDFD_GET_IPC_NAMESPACE: 427 case PIDFD_GET_MNT_NAMESPACE: 428 case PIDFD_GET_NET_NAMESPACE: 429 case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE: 430 case PIDFD_GET_TIME_NAMESPACE: 431 case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE: 432 case PIDFD_GET_UTS_NAMESPACE: 433 case PIDFD_GET_USER_NAMESPACE: 434 case PIDFD_GET_PID_NAMESPACE: 435 return true; 436 } 437 438 /* Extensible ioctls require some more careful checks. */ 439 switch (_IOC_NR(cmd)) { 440 case _IOC_NR(PIDFD_GET_INFO): 441 /* 442 * Try to prevent performing a pidfd ioctl when someone 443 * erronously mistook the file descriptor for a pidfd. 444 * This is not perfect but will catch most cases. 445 */ 446 return (_IOC_TYPE(cmd) == _IOC_TYPE(PIDFD_GET_INFO)); 447 } 448 449 return false; 450 } 451 452 static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg) 453 { 454 struct task_struct *task __free(put_task) = NULL; 455 struct nsproxy *nsp __free(put_nsproxy) = NULL; 456 struct ns_common *ns_common = NULL; 457 struct pid_namespace *pid_ns; 458 459 if (!pidfs_ioctl_valid(cmd)) 460 return -ENOIOCTLCMD; 461 462 if (cmd == FS_IOC_GETVERSION) { 463 if (!arg) 464 return -EINVAL; 465 466 __u32 __user *argp = (__u32 __user *)arg; 467 return put_user(file_inode(file)->i_generation, argp); 468 } 469 470 /* Extensible IOCTL that does not open namespace FDs, take a shortcut */ 471 if (_IOC_NR(cmd) == _IOC_NR(PIDFD_GET_INFO)) 472 return pidfd_info(file, cmd, arg); 473 474 task = get_pid_task(pidfd_pid(file), PIDTYPE_PID); 475 if (!task) 476 return -ESRCH; 477 478 if (arg) 479 return -EINVAL; 480 481 scoped_guard(task_lock, task) { 482 nsp = task->nsproxy; 483 if (nsp) 484 get_nsproxy(nsp); 485 } 486 if (!nsp) 487 return -ESRCH; /* just pretend it didn't exist */ 488 489 /* 490 * We're trying to open a file descriptor to the namespace so perform a 491 * filesystem cred ptrace check. Also, we mirror nsfs behavior. 492 */ 493 if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) 494 return -EACCES; 495 496 switch (cmd) { 497 /* Namespaces that hang of nsproxy. */ 498 case PIDFD_GET_CGROUP_NAMESPACE: 499 if (IS_ENABLED(CONFIG_CGROUPS)) { 500 get_cgroup_ns(nsp->cgroup_ns); 501 ns_common = to_ns_common(nsp->cgroup_ns); 502 } 503 break; 504 case PIDFD_GET_IPC_NAMESPACE: 505 if (IS_ENABLED(CONFIG_IPC_NS)) { 506 get_ipc_ns(nsp->ipc_ns); 507 ns_common = to_ns_common(nsp->ipc_ns); 508 } 509 break; 510 case PIDFD_GET_MNT_NAMESPACE: 511 get_mnt_ns(nsp->mnt_ns); 512 ns_common = to_ns_common(nsp->mnt_ns); 513 break; 514 case PIDFD_GET_NET_NAMESPACE: 515 if (IS_ENABLED(CONFIG_NET_NS)) { 516 ns_common = to_ns_common(nsp->net_ns); 517 get_net_ns(ns_common); 518 } 519 break; 520 case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE: 521 if (IS_ENABLED(CONFIG_PID_NS)) { 522 get_pid_ns(nsp->pid_ns_for_children); 523 ns_common = to_ns_common(nsp->pid_ns_for_children); 524 } 525 break; 526 case PIDFD_GET_TIME_NAMESPACE: 527 if (IS_ENABLED(CONFIG_TIME_NS)) { 528 get_time_ns(nsp->time_ns); 529 ns_common = to_ns_common(nsp->time_ns); 530 } 531 break; 532 case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE: 533 if (IS_ENABLED(CONFIG_TIME_NS)) { 534 get_time_ns(nsp->time_ns_for_children); 535 ns_common = to_ns_common(nsp->time_ns_for_children); 536 } 537 break; 538 case PIDFD_GET_UTS_NAMESPACE: 539 if (IS_ENABLED(CONFIG_UTS_NS)) { 540 get_uts_ns(nsp->uts_ns); 541 ns_common = to_ns_common(nsp->uts_ns); 542 } 543 break; 544 /* Namespaces that don't hang of nsproxy. */ 545 case PIDFD_GET_USER_NAMESPACE: 546 if (IS_ENABLED(CONFIG_USER_NS)) { 547 rcu_read_lock(); 548 ns_common = to_ns_common(get_user_ns(task_cred_xxx(task, user_ns))); 549 rcu_read_unlock(); 550 } 551 break; 552 case PIDFD_GET_PID_NAMESPACE: 553 if (IS_ENABLED(CONFIG_PID_NS)) { 554 rcu_read_lock(); 555 pid_ns = task_active_pid_ns(task); 556 if (pid_ns) 557 ns_common = to_ns_common(get_pid_ns(pid_ns)); 558 rcu_read_unlock(); 559 } 560 break; 561 default: 562 return -ENOIOCTLCMD; 563 } 564 565 if (!ns_common) 566 return -EOPNOTSUPP; 567 568 /* open_namespace() unconditionally consumes the reference */ 569 return open_namespace(ns_common); 570 } 571 572 static const struct file_operations pidfs_file_operations = { 573 .poll = pidfd_poll, 574 #ifdef CONFIG_PROC_FS 575 .show_fdinfo = pidfd_show_fdinfo, 576 #endif 577 .unlocked_ioctl = pidfd_ioctl, 578 .compat_ioctl = compat_ptr_ioctl, 579 }; 580 581 struct pid *pidfd_pid(const struct file *file) 582 { 583 if (file->f_op != &pidfs_file_operations) 584 return ERR_PTR(-EBADF); 585 return file_inode(file)->i_private; 586 } 587 588 /* 589 * We're called from release_task(). We know there's at least one 590 * reference to struct pid being held that won't be released until the 591 * task has been reaped which cannot happen until we're out of 592 * release_task(). 593 * 594 * If this struct pid has at least once been referred to by a pidfd then 595 * pid->attr will be allocated. If not we mark the struct pid as dead so 596 * anyone who is trying to register it with pidfs will fail to do so. 597 * Otherwise we would hand out pidfs for reaped tasks without having 598 * exit information available. 599 * 600 * Worst case is that we've filled in the info and the pid gets freed 601 * right away in free_pid() when no one holds a pidfd anymore. Since 602 * pidfs_exit() currently is placed after exit_task_work() we know that 603 * it cannot be us aka the exiting task holding a pidfd to itself. 604 */ 605 void pidfs_exit(struct task_struct *tsk) 606 { 607 struct pid *pid = task_pid(tsk); 608 struct pidfs_attr *attr; 609 struct pidfs_exit_info *exit_info; 610 #ifdef CONFIG_CGROUPS 611 struct cgroup *cgrp; 612 #endif 613 614 might_sleep(); 615 616 guard(spinlock_irq)(&pid->wait_pidfd.lock); 617 attr = pid->attr; 618 if (!attr) { 619 /* 620 * No one ever held a pidfd for this struct pid. 621 * Mark it as dead so no one can add a pidfs 622 * entry anymore. We're about to be reaped and 623 * so no exit information would be available. 624 */ 625 pid->attr = PIDFS_PID_DEAD; 626 return; 627 } 628 629 /* 630 * If @pid->attr is set someone might still legitimately hold a 631 * pidfd to @pid or someone might concurrently still be getting 632 * a reference to an already stashed dentry from @pid->stashed. 633 * So defer cleaning @pid->attr until the last reference to @pid 634 * is put 635 */ 636 637 exit_info = &attr->__pei; 638 639 #ifdef CONFIG_CGROUPS 640 rcu_read_lock(); 641 cgrp = task_dfl_cgroup(tsk); 642 exit_info->cgroupid = cgroup_id(cgrp); 643 rcu_read_unlock(); 644 #endif 645 exit_info->exit_code = tsk->exit_code; 646 647 /* Ensure that PIDFD_GET_INFO sees either all or nothing. */ 648 smp_store_release(&attr->exit_info, &attr->__pei); 649 } 650 651 #ifdef CONFIG_COREDUMP 652 void pidfs_coredump(const struct coredump_params *cprm) 653 { 654 struct pid *pid = cprm->pid; 655 struct pidfs_exit_info *exit_info; 656 struct pidfs_attr *attr; 657 __u32 coredump_mask = 0; 658 659 attr = READ_ONCE(pid->attr); 660 661 VFS_WARN_ON_ONCE(!attr); 662 VFS_WARN_ON_ONCE(attr == PIDFS_PID_DEAD); 663 664 exit_info = &attr->__pei; 665 /* Note how we were coredumped. */ 666 coredump_mask = pidfs_coredump_mask(cprm->mm_flags); 667 /* Note that we actually did coredump. */ 668 coredump_mask |= PIDFD_COREDUMPED; 669 /* If coredumping is set to skip we should never end up here. */ 670 VFS_WARN_ON_ONCE(coredump_mask & PIDFD_COREDUMP_SKIP); 671 smp_store_release(&exit_info->coredump_mask, coredump_mask); 672 } 673 #endif 674 675 static struct vfsmount *pidfs_mnt __ro_after_init; 676 677 /* 678 * The vfs falls back to simple_setattr() if i_op->setattr() isn't 679 * implemented. Let's reject it completely until we have a clean 680 * permission concept for pidfds. 681 */ 682 static int pidfs_setattr(struct mnt_idmap *idmap, struct dentry *dentry, 683 struct iattr *attr) 684 { 685 return anon_inode_setattr(idmap, dentry, attr); 686 } 687 688 static int pidfs_getattr(struct mnt_idmap *idmap, const struct path *path, 689 struct kstat *stat, u32 request_mask, 690 unsigned int query_flags) 691 { 692 return anon_inode_getattr(idmap, path, stat, request_mask, query_flags); 693 } 694 695 static ssize_t pidfs_listxattr(struct dentry *dentry, char *buf, size_t size) 696 { 697 struct inode *inode = d_inode(dentry); 698 struct pid *pid = inode->i_private; 699 struct pidfs_attr *attr = pid->attr; 700 struct simple_xattrs *xattrs; 701 702 xattrs = READ_ONCE(attr->xattrs); 703 if (!xattrs) 704 return 0; 705 706 return simple_xattr_list(inode, xattrs, buf, size); 707 } 708 709 static const struct inode_operations pidfs_inode_operations = { 710 .getattr = pidfs_getattr, 711 .setattr = pidfs_setattr, 712 .listxattr = pidfs_listxattr, 713 }; 714 715 static void pidfs_evict_inode(struct inode *inode) 716 { 717 struct pid *pid = inode->i_private; 718 719 clear_inode(inode); 720 put_pid(pid); 721 } 722 723 static const struct super_operations pidfs_sops = { 724 .drop_inode = generic_delete_inode, 725 .evict_inode = pidfs_evict_inode, 726 .statfs = simple_statfs, 727 }; 728 729 /* 730 * 'lsof' has knowledge of out historical anon_inode use, and expects 731 * the pidfs dentry name to start with 'anon_inode'. 732 */ 733 static char *pidfs_dname(struct dentry *dentry, char *buffer, int buflen) 734 { 735 return dynamic_dname(buffer, buflen, "anon_inode:[pidfd]"); 736 } 737 738 const struct dentry_operations pidfs_dentry_operations = { 739 .d_dname = pidfs_dname, 740 .d_prune = stashed_dentry_prune, 741 }; 742 743 static int pidfs_encode_fh(struct inode *inode, u32 *fh, int *max_len, 744 struct inode *parent) 745 { 746 const struct pid *pid = inode->i_private; 747 748 if (*max_len < 2) { 749 *max_len = 2; 750 return FILEID_INVALID; 751 } 752 753 *max_len = 2; 754 *(u64 *)fh = pid->ino; 755 return FILEID_KERNFS; 756 } 757 758 static int pidfs_ino_find(const void *key, const struct rb_node *node) 759 { 760 const u64 pid_ino = *(u64 *)key; 761 const struct pid *pid = rb_entry(node, struct pid, pidfs_node); 762 763 if (pid_ino < pid->ino) 764 return -1; 765 if (pid_ino > pid->ino) 766 return 1; 767 return 0; 768 } 769 770 /* Find a struct pid based on the inode number. */ 771 static struct pid *pidfs_ino_get_pid(u64 ino) 772 { 773 struct pid *pid; 774 struct rb_node *node; 775 unsigned int seq; 776 777 guard(rcu)(); 778 do { 779 seq = read_seqcount_begin(&pidmap_lock_seq); 780 node = rb_find_rcu(&ino, &pidfs_ino_tree, pidfs_ino_find); 781 if (node) 782 break; 783 } while (read_seqcount_retry(&pidmap_lock_seq, seq)); 784 785 if (!node) 786 return NULL; 787 788 pid = rb_entry(node, struct pid, pidfs_node); 789 790 /* Within our pid namespace hierarchy? */ 791 if (pid_vnr(pid) == 0) 792 return NULL; 793 794 return get_pid(pid); 795 } 796 797 static struct dentry *pidfs_fh_to_dentry(struct super_block *sb, 798 struct fid *fid, int fh_len, 799 int fh_type) 800 { 801 int ret; 802 u64 pid_ino; 803 struct path path; 804 struct pid *pid; 805 806 if (fh_len < 2) 807 return NULL; 808 809 switch (fh_type) { 810 case FILEID_KERNFS: 811 pid_ino = *(u64 *)fid; 812 break; 813 default: 814 return NULL; 815 } 816 817 pid = pidfs_ino_get_pid(pid_ino); 818 if (!pid) 819 return NULL; 820 821 ret = path_from_stashed(&pid->stashed, pidfs_mnt, pid, &path); 822 if (ret < 0) 823 return ERR_PTR(ret); 824 825 VFS_WARN_ON_ONCE(!pid->attr); 826 827 mntput(path.mnt); 828 return path.dentry; 829 } 830 831 /* 832 * Make sure that we reject any nonsensical flags that users pass via 833 * open_by_handle_at(). Note that PIDFD_THREAD is defined as O_EXCL, and 834 * PIDFD_NONBLOCK as O_NONBLOCK. 835 */ 836 #define VALID_FILE_HANDLE_OPEN_FLAGS \ 837 (O_RDONLY | O_WRONLY | O_RDWR | O_NONBLOCK | O_CLOEXEC | O_EXCL) 838 839 static int pidfs_export_permission(struct handle_to_path_ctx *ctx, 840 unsigned int oflags) 841 { 842 if (oflags & ~(VALID_FILE_HANDLE_OPEN_FLAGS | O_LARGEFILE)) 843 return -EINVAL; 844 845 /* 846 * pidfd_ino_get_pid() will verify that the struct pid is part 847 * of the caller's pid namespace hierarchy. No further 848 * permission checks are needed. 849 */ 850 return 0; 851 } 852 853 static struct file *pidfs_export_open(struct path *path, unsigned int oflags) 854 { 855 /* 856 * Clear O_LARGEFILE as open_by_handle_at() forces it and raise 857 * O_RDWR as pidfds always are. 858 */ 859 oflags &= ~O_LARGEFILE; 860 return dentry_open(path, oflags | O_RDWR, current_cred()); 861 } 862 863 static const struct export_operations pidfs_export_operations = { 864 .encode_fh = pidfs_encode_fh, 865 .fh_to_dentry = pidfs_fh_to_dentry, 866 .open = pidfs_export_open, 867 .permission = pidfs_export_permission, 868 }; 869 870 static int pidfs_init_inode(struct inode *inode, void *data) 871 { 872 const struct pid *pid = data; 873 874 inode->i_private = data; 875 inode->i_flags |= S_PRIVATE | S_ANON_INODE; 876 /* We allow to set xattrs. */ 877 inode->i_flags &= ~S_IMMUTABLE; 878 inode->i_mode |= S_IRWXU; 879 inode->i_op = &pidfs_inode_operations; 880 inode->i_fop = &pidfs_file_operations; 881 inode->i_ino = pidfs_ino(pid->ino); 882 inode->i_generation = pidfs_gen(pid->ino); 883 return 0; 884 } 885 886 static void pidfs_put_data(void *data) 887 { 888 struct pid *pid = data; 889 put_pid(pid); 890 } 891 892 /** 893 * pidfs_register_pid - register a struct pid in pidfs 894 * @pid: pid to pin 895 * 896 * Register a struct pid in pidfs. 897 * 898 * Return: On success zero, on error a negative error code is returned. 899 */ 900 int pidfs_register_pid(struct pid *pid) 901 { 902 struct pidfs_attr *new_attr __free(kfree) = NULL; 903 struct pidfs_attr *attr; 904 905 might_sleep(); 906 907 if (!pid) 908 return 0; 909 910 attr = READ_ONCE(pid->attr); 911 if (unlikely(attr == PIDFS_PID_DEAD)) 912 return PTR_ERR(PIDFS_PID_DEAD); 913 if (attr) 914 return 0; 915 916 new_attr = kmem_cache_zalloc(pidfs_attr_cachep, GFP_KERNEL); 917 if (!new_attr) 918 return -ENOMEM; 919 920 /* Synchronize with pidfs_exit(). */ 921 guard(spinlock_irq)(&pid->wait_pidfd.lock); 922 923 attr = pid->attr; 924 if (unlikely(attr == PIDFS_PID_DEAD)) 925 return PTR_ERR(PIDFS_PID_DEAD); 926 if (unlikely(attr)) 927 return 0; 928 929 pid->attr = no_free_ptr(new_attr); 930 return 0; 931 } 932 933 static struct dentry *pidfs_stash_dentry(struct dentry **stashed, 934 struct dentry *dentry) 935 { 936 int ret; 937 struct pid *pid = d_inode(dentry)->i_private; 938 939 VFS_WARN_ON_ONCE(stashed != &pid->stashed); 940 941 ret = pidfs_register_pid(pid); 942 if (ret) 943 return ERR_PTR(ret); 944 945 return stash_dentry(stashed, dentry); 946 } 947 948 static const struct stashed_operations pidfs_stashed_ops = { 949 .stash_dentry = pidfs_stash_dentry, 950 .init_inode = pidfs_init_inode, 951 .put_data = pidfs_put_data, 952 }; 953 954 static int pidfs_xattr_get(const struct xattr_handler *handler, 955 struct dentry *unused, struct inode *inode, 956 const char *suffix, void *value, size_t size) 957 { 958 struct pid *pid = inode->i_private; 959 struct pidfs_attr *attr = pid->attr; 960 const char *name; 961 struct simple_xattrs *xattrs; 962 963 xattrs = READ_ONCE(attr->xattrs); 964 if (!xattrs) 965 return 0; 966 967 name = xattr_full_name(handler, suffix); 968 return simple_xattr_get(xattrs, name, value, size); 969 } 970 971 static int pidfs_xattr_set(const struct xattr_handler *handler, 972 struct mnt_idmap *idmap, struct dentry *unused, 973 struct inode *inode, const char *suffix, 974 const void *value, size_t size, int flags) 975 { 976 struct pid *pid = inode->i_private; 977 struct pidfs_attr *attr = pid->attr; 978 const char *name; 979 struct simple_xattrs *xattrs; 980 struct simple_xattr *old_xattr; 981 982 /* Ensure we're the only one to set @attr->xattrs. */ 983 WARN_ON_ONCE(!inode_is_locked(inode)); 984 985 xattrs = READ_ONCE(attr->xattrs); 986 if (!xattrs) { 987 xattrs = kmem_cache_zalloc(pidfs_xattr_cachep, GFP_KERNEL); 988 if (!xattrs) 989 return -ENOMEM; 990 991 simple_xattrs_init(xattrs); 992 smp_store_release(&pid->attr->xattrs, xattrs); 993 } 994 995 name = xattr_full_name(handler, suffix); 996 old_xattr = simple_xattr_set(xattrs, name, value, size, flags); 997 if (IS_ERR(old_xattr)) 998 return PTR_ERR(old_xattr); 999 1000 simple_xattr_free(old_xattr); 1001 return 0; 1002 } 1003 1004 static const struct xattr_handler pidfs_trusted_xattr_handler = { 1005 .prefix = XATTR_TRUSTED_PREFIX, 1006 .get = pidfs_xattr_get, 1007 .set = pidfs_xattr_set, 1008 }; 1009 1010 static const struct xattr_handler *const pidfs_xattr_handlers[] = { 1011 &pidfs_trusted_xattr_handler, 1012 NULL 1013 }; 1014 1015 static int pidfs_init_fs_context(struct fs_context *fc) 1016 { 1017 struct pseudo_fs_context *ctx; 1018 1019 ctx = init_pseudo(fc, PID_FS_MAGIC); 1020 if (!ctx) 1021 return -ENOMEM; 1022 1023 fc->s_iflags |= SB_I_NOEXEC; 1024 fc->s_iflags |= SB_I_NODEV; 1025 ctx->ops = &pidfs_sops; 1026 ctx->eops = &pidfs_export_operations; 1027 ctx->dops = &pidfs_dentry_operations; 1028 ctx->xattr = pidfs_xattr_handlers; 1029 fc->s_fs_info = (void *)&pidfs_stashed_ops; 1030 return 0; 1031 } 1032 1033 static struct file_system_type pidfs_type = { 1034 .name = "pidfs", 1035 .init_fs_context = pidfs_init_fs_context, 1036 .kill_sb = kill_anon_super, 1037 }; 1038 1039 struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags) 1040 { 1041 struct file *pidfd_file; 1042 struct path path __free(path_put) = {}; 1043 int ret; 1044 1045 /* 1046 * Ensure that PIDFD_STALE can be passed as a flag without 1047 * overloading other uapi pidfd flags. 1048 */ 1049 BUILD_BUG_ON(PIDFD_STALE == PIDFD_THREAD); 1050 BUILD_BUG_ON(PIDFD_STALE == PIDFD_NONBLOCK); 1051 1052 ret = path_from_stashed(&pid->stashed, pidfs_mnt, get_pid(pid), &path); 1053 if (ret < 0) 1054 return ERR_PTR(ret); 1055 1056 VFS_WARN_ON_ONCE(!pid->attr); 1057 1058 flags &= ~PIDFD_STALE; 1059 flags |= O_RDWR; 1060 pidfd_file = dentry_open(&path, flags, current_cred()); 1061 /* Raise PIDFD_THREAD explicitly as do_dentry_open() strips it. */ 1062 if (!IS_ERR(pidfd_file)) 1063 pidfd_file->f_flags |= (flags & PIDFD_THREAD); 1064 1065 return pidfd_file; 1066 } 1067 1068 void __init pidfs_init(void) 1069 { 1070 pidfs_attr_cachep = kmem_cache_create("pidfs_attr_cache", sizeof(struct pidfs_attr), 0, 1071 (SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT | 1072 SLAB_ACCOUNT | SLAB_PANIC), NULL); 1073 1074 pidfs_xattr_cachep = kmem_cache_create("pidfs_xattr_cache", 1075 sizeof(struct simple_xattrs), 0, 1076 (SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT | 1077 SLAB_ACCOUNT | SLAB_PANIC), NULL); 1078 1079 pidfs_mnt = kern_mount(&pidfs_type); 1080 if (IS_ERR(pidfs_mnt)) 1081 panic("Failed to mount pidfs pseudo filesystem"); 1082 1083 pidfs_root_path.mnt = pidfs_mnt; 1084 pidfs_root_path.dentry = pidfs_mnt->mnt_root; 1085 } 1086