1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/anon_inodes.h> 3 #include <linux/compat.h> 4 #include <linux/exportfs.h> 5 #include <linux/file.h> 6 #include <linux/fs.h> 7 #include <linux/cgroup.h> 8 #include <linux/magic.h> 9 #include <linux/mount.h> 10 #include <linux/pid.h> 11 #include <linux/pidfs.h> 12 #include <linux/sched/signal.h> 13 #include <linux/signal.h> 14 #include <linux/pid_namespace.h> 15 #include <linux/poll.h> 16 #include <linux/proc_fs.h> 17 #include <linux/proc_ns.h> 18 #include <linux/pseudo_fs.h> 19 #include <linux/ptrace.h> 20 #include <linux/seq_file.h> 21 #include <uapi/linux/pidfd.h> 22 #include <linux/ipc_namespace.h> 23 #include <linux/time_namespace.h> 24 #include <linux/utsname.h> 25 #include <net/net_namespace.h> 26 #include <linux/coredump.h> 27 #include <linux/rhashtable.h> 28 #include <linux/llist.h> 29 #include <linux/xattr.h> 30 #include <linux/cookie.h> 31 32 #include "internal.h" 33 #include "mount.h" 34 35 #define PIDFS_PID_DEAD ERR_PTR(-ESRCH) 36 37 static struct kmem_cache *pidfs_attr_cachep __ro_after_init; 38 39 static struct path pidfs_root_path = {}; 40 41 static struct simple_xattr_cache pidfs_xa_cache; 42 43 void pidfs_get_root(struct path *path) 44 { 45 *path = pidfs_root_path; 46 path_get(path); 47 } 48 49 enum pidfs_attr_mask_bits { 50 PIDFS_ATTR_BIT_EXIT = 0, 51 PIDFS_ATTR_BIT_COREDUMP = 1, 52 }; 53 54 struct pidfs_anon_attr { 55 unsigned long attr_mask; 56 struct /* exit info */ { 57 __u64 cgroupid; 58 __s32 exit_code; 59 }; 60 __u32 coredump_mask; 61 __u32 coredump_signal; 62 __u32 coredump_code; 63 }; 64 65 static struct rhashtable pidfs_ino_ht; 66 67 static const struct rhashtable_params pidfs_ino_ht_params = { 68 .key_offset = offsetof(struct pid, ino), 69 .key_len = sizeof(u64), 70 .head_offset = offsetof(struct pid, pidfs_hash), 71 .automatic_shrinking = true, 72 }; 73 74 /* 75 * inode number handling 76 * 77 * On 64 bit nothing special happens. The 64bit number assigned 78 * to struct pid is the inode number. 79 * 80 * On 32 bit the 64 bit number assigned to struct pid is split 81 * into two 32 bit numbers. The lower 32 bits are used as the 82 * inode number and the upper 32 bits are used as the inode 83 * generation number. 84 * 85 * On 32 bit pidfs_ino() will return the lower 32 bit. When 86 * pidfs_ino() returns zero a wrap around happened. When a 87 * wraparound happens the 64 bit number will be incremented by 1 88 * so inode numbering starts at 1 again. 89 * 90 * On 64 bit comparing two pidfds is as simple as comparing 91 * inode numbers. 92 * 93 * When a wraparound happens on 32 bit multiple pidfds with the 94 * same inode number are likely to exist (This isn't a problem 95 * since before pidfs pidfds used the anonymous inode meaning 96 * all pidfds had the same inode number.). Userspace can 97 * reconstruct the 64 bit identifier by retrieving both the 98 * inode number and the inode generation number to compare or 99 * use file handles. 100 */ 101 struct pidfs_attr { 102 struct list_head xattrs; 103 union { 104 struct pidfs_anon_attr; 105 struct llist_node pidfs_llist; 106 }; 107 }; 108 109 #if BITS_PER_LONG == 32 110 111 static DEFINE_SPINLOCK(pidfs_ino_lock); 112 static u64 pidfs_ino_nr = 1; 113 114 static inline unsigned long pidfs_ino(u64 ino) 115 { 116 return lower_32_bits(ino); 117 } 118 119 /* On 32 bit the generation number are the upper 32 bits. */ 120 static inline u32 pidfs_gen(u64 ino) 121 { 122 return upper_32_bits(ino); 123 } 124 125 static inline u64 pidfs_alloc_ino(void) 126 { 127 u64 ino; 128 129 spin_lock(&pidfs_ino_lock); 130 if (pidfs_ino(pidfs_ino_nr) == 0) 131 pidfs_ino_nr++; 132 ino = pidfs_ino_nr++; 133 spin_unlock(&pidfs_ino_lock); 134 return ino; 135 } 136 137 #else 138 139 /* On 64 bit simply return ino. */ 140 static inline unsigned long pidfs_ino(u64 ino) 141 { 142 return ino; 143 } 144 145 /* On 64 bit the generation number is 0. */ 146 static inline u32 pidfs_gen(u64 ino) 147 { 148 return 0; 149 } 150 151 DEFINE_COOKIE(pidfs_ino_cookie); 152 153 static u64 pidfs_alloc_ino(void) 154 { 155 u64 ino; 156 157 preempt_disable(); 158 ino = gen_cookie_next(&pidfs_ino_cookie); 159 preempt_enable(); 160 161 VFS_WARN_ON_ONCE(ino < 1); 162 return ino; 163 } 164 165 #endif 166 167 void pidfs_prepare_pid(struct pid *pid) 168 { 169 pid->stashed = NULL; 170 pid->attr = NULL; 171 pid->ino = 0; 172 } 173 174 int pidfs_add_pid(struct pid *pid) 175 { 176 int ret; 177 178 pid->ino = pidfs_alloc_ino(); 179 ret = rhashtable_insert_fast(&pidfs_ino_ht, &pid->pidfs_hash, 180 pidfs_ino_ht_params); 181 if (unlikely(ret)) 182 pid->ino = 0; 183 return ret; 184 } 185 186 void pidfs_remove_pid(struct pid *pid) 187 { 188 if (likely(pid->ino)) 189 rhashtable_remove_fast(&pidfs_ino_ht, &pid->pidfs_hash, 190 pidfs_ino_ht_params); 191 } 192 193 static LLIST_HEAD(pidfs_free_list); 194 195 static void pidfs_free_attr_work(struct work_struct *work) 196 { 197 struct pidfs_attr *attr, *next; 198 struct llist_node *head; 199 200 head = llist_del_all(&pidfs_free_list); 201 llist_for_each_entry_safe(attr, next, head, pidfs_llist) { 202 simple_xattrs_free(&pidfs_xa_cache, &attr->xattrs, NULL); 203 kfree(attr); 204 } 205 } 206 207 static DECLARE_WORK(pidfs_free_work, pidfs_free_attr_work); 208 209 void pidfs_free_pid(struct pid *pid) 210 { 211 struct pidfs_attr *attr = pid->attr; 212 213 /* 214 * Any dentry must've been wiped from the pid by now. 215 * Otherwise there's a reference count bug. 216 */ 217 VFS_WARN_ON_ONCE(pid->stashed); 218 219 /* 220 * This if an error occurred during e.g., task creation that 221 * causes us to never go through the exit path. 222 */ 223 if (unlikely(!attr)) 224 return; 225 226 /* This never had a pidfd created. */ 227 if (IS_ERR(attr)) 228 return; 229 230 if (likely(list_empty(&attr->xattrs))) 231 kfree(attr); 232 else if (llist_add(&attr->pidfs_llist, &pidfs_free_list)) 233 schedule_work(&pidfs_free_work); 234 } 235 236 #ifdef CONFIG_PROC_FS 237 /** 238 * pidfd_show_fdinfo - print information about a pidfd 239 * @m: proc fdinfo file 240 * @f: file referencing a pidfd 241 * 242 * Pid: 243 * This function will print the pid that a given pidfd refers to in the 244 * pid namespace of the procfs instance. 245 * If the pid namespace of the process is not a descendant of the pid 246 * namespace of the procfs instance 0 will be shown as its pid. This is 247 * similar to calling getppid() on a process whose parent is outside of 248 * its pid namespace. 249 * 250 * NSpid: 251 * If pid namespaces are supported then this function will also print 252 * the pid of a given pidfd refers to for all descendant pid namespaces 253 * starting from the current pid namespace of the instance, i.e. the 254 * Pid field and the first entry in the NSpid field will be identical. 255 * If the pid namespace of the process is not a descendant of the pid 256 * namespace of the procfs instance 0 will be shown as its first NSpid 257 * entry and no others will be shown. 258 * Note that this differs from the Pid and NSpid fields in 259 * /proc/<pid>/status where Pid and NSpid are always shown relative to 260 * the pid namespace of the procfs instance. The difference becomes 261 * obvious when sending around a pidfd between pid namespaces from a 262 * different branch of the tree, i.e. where no ancestral relation is 263 * present between the pid namespaces: 264 * - create two new pid namespaces ns1 and ns2 in the initial pid 265 * namespace (also take care to create new mount namespaces in the 266 * new pid namespace and mount procfs) 267 * - create a process with a pidfd in ns1 268 * - send pidfd from ns1 to ns2 269 * - read /proc/self/fdinfo/<pidfd> and observe that both Pid and NSpid 270 * have exactly one entry, which is 0 271 */ 272 static void pidfd_show_fdinfo(struct seq_file *m, struct file *f) 273 { 274 struct pid *pid = pidfd_pid(f); 275 struct pid_namespace *ns; 276 pid_t nr = -1; 277 278 if (likely(pid_has_task(pid, PIDTYPE_PID))) { 279 ns = proc_pid_ns(file_inode(m->file)->i_sb); 280 nr = pid_nr_ns(pid, ns); 281 } 282 283 seq_put_decimal_ll(m, "Pid:\t", nr); 284 285 #ifdef CONFIG_PID_NS 286 seq_put_decimal_ll(m, "\nNSpid:\t", nr); 287 if (nr > 0) { 288 int i; 289 290 /* If nr is non-zero it means that 'pid' is valid and that 291 * ns, i.e. the pid namespace associated with the procfs 292 * instance, is in the pid namespace hierarchy of pid. 293 * Start at one below the already printed level. 294 */ 295 for (i = ns->level + 1; i <= pid->level; i++) 296 seq_put_decimal_ll(m, "\t", pid->numbers[i].nr); 297 } 298 #endif 299 seq_putc(m, '\n'); 300 } 301 #endif 302 303 /* 304 * Poll support for process exit notification. 305 */ 306 static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts) 307 { 308 struct pid *pid = pidfd_pid(file); 309 struct task_struct *task; 310 __poll_t poll_flags = 0; 311 312 poll_wait(file, &pid->wait_pidfd, pts); 313 /* 314 * Don't wake waiters if the thread-group leader exited 315 * prematurely. They either get notified when the last subthread 316 * exits or not at all if one of the remaining subthreads execs 317 * and assumes the struct pid of the old thread-group leader. 318 */ 319 guard(rcu)(); 320 task = pid_task(pid, PIDTYPE_PID); 321 if (!task) 322 poll_flags = EPOLLIN | EPOLLRDNORM | EPOLLHUP; 323 else if (task->exit_state && !delay_group_leader(task)) 324 poll_flags = EPOLLIN | EPOLLRDNORM; 325 326 return poll_flags; 327 } 328 329 static inline bool pid_in_current_pidns(const struct pid *pid) 330 { 331 const struct pid_namespace *ns = task_active_pid_ns(current); 332 333 if (ns->level <= pid->level) 334 return pid->numbers[ns->level].ns == ns; 335 336 return false; 337 } 338 339 static __u32 pidfs_coredump_mask(enum task_dumpable dumpable) 340 { 341 switch (dumpable) { 342 case TASK_DUMPABLE_OWNER: 343 return PIDFD_COREDUMP_USER; 344 case TASK_DUMPABLE_ROOT: 345 return PIDFD_COREDUMP_ROOT; 346 case TASK_DUMPABLE_OFF: 347 return PIDFD_COREDUMP_SKIP; 348 default: 349 WARN_ON_ONCE(true); 350 } 351 352 return 0; 353 } 354 355 /* This must be updated whenever a new flag is added */ 356 #define PIDFD_INFO_SUPPORTED (PIDFD_INFO_PID | \ 357 PIDFD_INFO_CREDS | \ 358 PIDFD_INFO_CGROUPID | \ 359 PIDFD_INFO_EXIT | \ 360 PIDFD_INFO_COREDUMP | \ 361 PIDFD_INFO_SUPPORTED_MASK | \ 362 PIDFD_INFO_COREDUMP_SIGNAL | \ 363 PIDFD_INFO_COREDUMP_CODE) 364 365 static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg) 366 { 367 struct pidfd_info __user *uinfo = (struct pidfd_info __user *)arg; 368 struct task_struct *task __free(put_task) = NULL; 369 struct pid *pid = pidfd_pid(file); 370 size_t usize = _IOC_SIZE(cmd); 371 struct pidfd_info kinfo = {}; 372 struct user_namespace *user_ns; 373 struct pidfs_attr *attr; 374 const struct cred *c; 375 __u64 mask; 376 377 BUILD_BUG_ON(sizeof(struct pidfd_info) != PIDFD_INFO_SIZE_VER3); 378 379 if (!uinfo) 380 return -EINVAL; 381 if (usize < PIDFD_INFO_SIZE_VER0) 382 return -EINVAL; /* First version, no smaller struct possible */ 383 384 if (copy_from_user(&mask, &uinfo->mask, sizeof(mask))) 385 return -EFAULT; 386 387 /* 388 * Restrict information retrieval to tasks within the caller's pid 389 * namespace hierarchy. 390 */ 391 if (!pid_in_current_pidns(pid)) 392 return -EREMOTE; 393 394 attr = READ_ONCE(pid->attr); 395 if (mask & PIDFD_INFO_EXIT) { 396 if (test_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask)) { 397 smp_rmb(); 398 kinfo.mask |= PIDFD_INFO_EXIT; 399 #ifdef CONFIG_CGROUPS 400 kinfo.cgroupid = attr->cgroupid; 401 kinfo.mask |= PIDFD_INFO_CGROUPID; 402 #endif 403 kinfo.exit_code = attr->exit_code; 404 } 405 } 406 407 if (mask & PIDFD_INFO_COREDUMP) { 408 if (test_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask)) { 409 smp_rmb(); 410 kinfo.mask |= PIDFD_INFO_COREDUMP | PIDFD_INFO_COREDUMP_SIGNAL | PIDFD_INFO_COREDUMP_CODE; 411 kinfo.coredump_mask = attr->coredump_mask; 412 kinfo.coredump_signal = attr->coredump_signal; 413 kinfo.coredump_code = attr->coredump_code; 414 } 415 } 416 417 task = get_pid_task(pid, PIDTYPE_PID); 418 if (!task) { 419 /* 420 * If the task has already been reaped, only exit 421 * information is available 422 */ 423 if (!(mask & PIDFD_INFO_EXIT)) 424 return -ESRCH; 425 426 goto copy_out; 427 } 428 429 c = get_task_cred(task); 430 if (!c) 431 return -ESRCH; 432 433 if ((mask & PIDFD_INFO_COREDUMP) && !kinfo.coredump_mask) { 434 kinfo.coredump_mask = pidfs_coredump_mask(task_exec_state_get_dumpable(task)); 435 kinfo.mask |= PIDFD_INFO_COREDUMP; 436 /* No coredump actually took place, so no coredump signal. */ 437 } 438 439 /* Unconditionally return identifiers and credentials, the rest only on request */ 440 441 user_ns = current_user_ns(); 442 kinfo.ruid = from_kuid_munged(user_ns, c->uid); 443 kinfo.rgid = from_kgid_munged(user_ns, c->gid); 444 kinfo.euid = from_kuid_munged(user_ns, c->euid); 445 kinfo.egid = from_kgid_munged(user_ns, c->egid); 446 kinfo.suid = from_kuid_munged(user_ns, c->suid); 447 kinfo.sgid = from_kgid_munged(user_ns, c->sgid); 448 kinfo.fsuid = from_kuid_munged(user_ns, c->fsuid); 449 kinfo.fsgid = from_kgid_munged(user_ns, c->fsgid); 450 kinfo.mask |= PIDFD_INFO_CREDS; 451 put_cred(c); 452 453 #ifdef CONFIG_CGROUPS 454 if (!kinfo.cgroupid) { 455 struct cgroup *cgrp; 456 457 rcu_read_lock(); 458 cgrp = task_dfl_cgroup(task); 459 kinfo.cgroupid = cgroup_id(cgrp); 460 kinfo.mask |= PIDFD_INFO_CGROUPID; 461 rcu_read_unlock(); 462 } 463 #endif 464 465 /* 466 * Copy pid/tgid last, to reduce the chances the information might be 467 * stale. Note that it is not possible to ensure it will be valid as the 468 * task might return as soon as the copy_to_user finishes, but that's ok 469 * and userspace expects that might happen and can act accordingly, so 470 * this is just best-effort. What we can do however is checking that all 471 * the fields are set correctly, or return ESRCH to avoid providing 472 * incomplete information. */ 473 474 kinfo.ppid = task_ppid_vnr(task); 475 kinfo.tgid = task_tgid_vnr(task); 476 kinfo.pid = task_pid_vnr(task); 477 kinfo.mask |= PIDFD_INFO_PID; 478 479 if (kinfo.pid == 0 || kinfo.tgid == 0) 480 return -ESRCH; 481 482 copy_out: 483 if (mask & PIDFD_INFO_SUPPORTED_MASK) { 484 kinfo.mask |= PIDFD_INFO_SUPPORTED_MASK; 485 kinfo.supported_mask = PIDFD_INFO_SUPPORTED; 486 } 487 488 /* Are there bits in the return mask not present in PIDFD_INFO_SUPPORTED? */ 489 WARN_ON_ONCE(~PIDFD_INFO_SUPPORTED & kinfo.mask); 490 /* 491 * If userspace and the kernel have the same struct size it can just 492 * be copied. If userspace provides an older struct, only the bits that 493 * userspace knows about will be copied. If userspace provides a new 494 * struct, only the bits that the kernel knows about will be copied. 495 */ 496 return copy_struct_to_user(uinfo, usize, &kinfo, sizeof(kinfo), NULL); 497 } 498 499 static bool pidfs_ioctl_valid(unsigned int cmd) 500 { 501 switch (cmd) { 502 case FS_IOC_GETVERSION: 503 case PIDFD_GET_CGROUP_NAMESPACE: 504 case PIDFD_GET_IPC_NAMESPACE: 505 case PIDFD_GET_MNT_NAMESPACE: 506 case PIDFD_GET_NET_NAMESPACE: 507 case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE: 508 case PIDFD_GET_TIME_NAMESPACE: 509 case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE: 510 case PIDFD_GET_UTS_NAMESPACE: 511 case PIDFD_GET_USER_NAMESPACE: 512 case PIDFD_GET_PID_NAMESPACE: 513 return true; 514 } 515 516 /* Extensible ioctls require some more careful checks. */ 517 switch (_IOC_NR(cmd)) { 518 case _IOC_NR(PIDFD_GET_INFO): 519 /* 520 * Try to prevent performing a pidfd ioctl when someone 521 * erronously mistook the file descriptor for a pidfd. 522 * This is not perfect but will catch most cases. 523 */ 524 return extensible_ioctl_valid(cmd, PIDFD_GET_INFO, PIDFD_INFO_SIZE_VER0); 525 } 526 527 return false; 528 } 529 530 static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg) 531 { 532 struct task_struct *task __free(put_task) = NULL; 533 struct nsproxy *nsp __free(put_nsproxy) = NULL; 534 struct ns_common *ns_common = NULL; 535 536 if (!pidfs_ioctl_valid(cmd)) 537 return -ENOIOCTLCMD; 538 539 if (cmd == FS_IOC_GETVERSION) { 540 if (!arg) 541 return -EINVAL; 542 543 __u32 __user *argp = (__u32 __user *)arg; 544 return put_user(file_inode(file)->i_generation, argp); 545 } 546 547 /* Extensible IOCTL that does not open namespace FDs, take a shortcut */ 548 if (_IOC_NR(cmd) == _IOC_NR(PIDFD_GET_INFO)) 549 return pidfd_info(file, cmd, arg); 550 551 task = get_pid_task(pidfd_pid(file), PIDTYPE_PID); 552 if (!task) 553 return -ESRCH; 554 555 if (arg) 556 return -EINVAL; 557 558 scoped_guard(task_lock, task) { 559 nsp = task->nsproxy; 560 if (nsp) 561 get_nsproxy(nsp); 562 } 563 if (!nsp) 564 return -ESRCH; /* just pretend it didn't exist */ 565 566 /* 567 * We're trying to open a file descriptor to the namespace so perform a 568 * filesystem cred ptrace check. Also, we mirror nsfs behavior. 569 */ 570 if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) 571 return -EACCES; 572 573 switch (cmd) { 574 /* Namespaces that hang of nsproxy. */ 575 case PIDFD_GET_CGROUP_NAMESPACE: 576 #ifdef CONFIG_CGROUPS 577 if (!ns_ref_get(nsp->cgroup_ns)) 578 break; 579 ns_common = to_ns_common(nsp->cgroup_ns); 580 #endif 581 break; 582 case PIDFD_GET_IPC_NAMESPACE: 583 #ifdef CONFIG_IPC_NS 584 if (!ns_ref_get(nsp->ipc_ns)) 585 break; 586 ns_common = to_ns_common(nsp->ipc_ns); 587 #endif 588 break; 589 case PIDFD_GET_MNT_NAMESPACE: 590 if (!ns_ref_get(nsp->mnt_ns)) 591 break; 592 ns_common = to_ns_common(nsp->mnt_ns); 593 break; 594 case PIDFD_GET_NET_NAMESPACE: 595 #ifdef CONFIG_NET_NS 596 if (!ns_ref_get(nsp->net_ns)) 597 break; 598 ns_common = to_ns_common(nsp->net_ns); 599 #endif 600 break; 601 case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE: 602 #ifdef CONFIG_PID_NS 603 if (!ns_ref_get(nsp->pid_ns_for_children)) 604 break; 605 ns_common = to_ns_common(nsp->pid_ns_for_children); 606 #endif 607 break; 608 case PIDFD_GET_TIME_NAMESPACE: 609 #ifdef CONFIG_TIME_NS 610 if (!ns_ref_get(nsp->time_ns)) 611 break; 612 ns_common = to_ns_common(nsp->time_ns); 613 #endif 614 break; 615 case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE: 616 #ifdef CONFIG_TIME_NS 617 if (!ns_ref_get(nsp->time_ns_for_children)) 618 break; 619 ns_common = to_ns_common(nsp->time_ns_for_children); 620 #endif 621 break; 622 case PIDFD_GET_UTS_NAMESPACE: 623 #ifdef CONFIG_UTS_NS 624 if (!ns_ref_get(nsp->uts_ns)) 625 break; 626 ns_common = to_ns_common(nsp->uts_ns); 627 #endif 628 break; 629 /* Namespaces that don't hang of nsproxy. */ 630 case PIDFD_GET_USER_NAMESPACE: 631 #ifdef CONFIG_USER_NS 632 scoped_guard(rcu) { 633 struct user_namespace *user_ns; 634 635 user_ns = task_cred_xxx(task, user_ns); 636 if (ns_ref_get(user_ns)) 637 ns_common = to_ns_common(user_ns); 638 } 639 #endif 640 break; 641 case PIDFD_GET_PID_NAMESPACE: 642 #ifdef CONFIG_PID_NS 643 scoped_guard(rcu) { 644 struct pid_namespace *pid_ns; 645 646 pid_ns = task_active_pid_ns(task); 647 if (ns_ref_get(pid_ns)) 648 ns_common = to_ns_common(pid_ns); 649 } 650 #endif 651 break; 652 default: 653 return -ENOIOCTLCMD; 654 } 655 656 if (!ns_common) 657 return -EOPNOTSUPP; 658 659 /* open_namespace() unconditionally consumes the reference */ 660 return open_namespace(ns_common); 661 } 662 663 #ifdef CONFIG_COMPAT 664 static long pidfd_compat_ioctl(struct file *file, unsigned int cmd, 665 unsigned long arg) 666 { 667 if (cmd == FS_IOC32_GETVERSION) 668 cmd = FS_IOC_GETVERSION; 669 670 return pidfd_ioctl(file, cmd, (unsigned long)compat_ptr(arg)); 671 } 672 #endif 673 674 static int pidfs_file_release(struct inode *inode, struct file *file) 675 { 676 struct pid *pid = inode->i_private; 677 struct task_struct *task; 678 679 if (!(file->f_flags & PIDFD_AUTOKILL)) 680 return 0; 681 682 guard(rcu)(); 683 task = pid_task(pid, PIDTYPE_TGID); 684 if (!task) 685 return 0; 686 687 /* Not available for kthreads or user workers for now. */ 688 if (WARN_ON_ONCE(task->flags & (PF_KTHREAD | PF_USER_WORKER))) 689 return 0; 690 do_send_sig_info(SIGKILL, SEND_SIG_PRIV, task, PIDTYPE_TGID); 691 return 0; 692 } 693 694 static const struct file_operations pidfs_file_operations = { 695 .release = pidfs_file_release, 696 .poll = pidfd_poll, 697 #ifdef CONFIG_PROC_FS 698 .show_fdinfo = pidfd_show_fdinfo, 699 #endif 700 .unlocked_ioctl = pidfd_ioctl, 701 #ifdef CONFIG_COMPAT 702 .compat_ioctl = pidfd_compat_ioctl, 703 #endif 704 }; 705 706 struct pid *pidfd_pid(const struct file *file) 707 { 708 if (file->f_op != &pidfs_file_operations) 709 return ERR_PTR(-EBADF); 710 return file_inode(file)->i_private; 711 } 712 713 /* 714 * We're called from release_task(). We know there's at least one 715 * reference to struct pid being held that won't be released until the 716 * task has been reaped which cannot happen until we're out of 717 * release_task(). 718 * 719 * If this struct pid has at least once been referred to by a pidfd then 720 * pid->attr will be allocated. If not we mark the struct pid as dead so 721 * anyone who is trying to register it with pidfs will fail to do so. 722 * Otherwise we would hand out pidfs for reaped tasks without having 723 * exit information available. 724 * 725 * Worst case is that we've filled in the info and the pid gets freed 726 * right away in free_pid() when no one holds a pidfd anymore. Since 727 * pidfs_exit() currently is placed after exit_task_work() we know that 728 * it cannot be us aka the exiting task holding a pidfd to itself. 729 */ 730 void pidfs_exit(struct task_struct *tsk) 731 { 732 struct pid *pid = task_pid(tsk); 733 struct pidfs_attr *attr; 734 #ifdef CONFIG_CGROUPS 735 struct cgroup *cgrp; 736 #endif 737 738 might_sleep(); 739 740 /* Synchronize with pidfs_register_pid(). */ 741 scoped_guard(spinlock_irq, &pid->wait_pidfd.lock) { 742 attr = pid->attr; 743 if (!attr) { 744 /* 745 * No one ever held a pidfd for this struct pid. 746 * Mark it as dead so no one can add a pidfs 747 * entry anymore. We're about to be reaped and 748 * so no exit information would be available. 749 */ 750 pid->attr = PIDFS_PID_DEAD; 751 return; 752 } 753 } 754 755 /* 756 * If @pid->attr is set someone might still legitimately hold a 757 * pidfd to @pid or someone might concurrently still be getting 758 * a reference to an already stashed dentry from @pid->stashed. 759 * So defer cleaning @pid->attr until the last reference to @pid 760 * is put 761 */ 762 763 #ifdef CONFIG_CGROUPS 764 rcu_read_lock(); 765 cgrp = task_dfl_cgroup(tsk); 766 attr->cgroupid = cgroup_id(cgrp); 767 rcu_read_unlock(); 768 #endif 769 attr->exit_code = tsk->exit_code; 770 771 /* Ensure that PIDFD_GET_INFO sees either all or nothing. */ 772 smp_wmb(); 773 set_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask); 774 } 775 776 #ifdef CONFIG_COREDUMP 777 void pidfs_coredump(const struct coredump_params *cprm) 778 { 779 struct pid *pid = cprm->pid; 780 struct pidfs_attr *attr; 781 782 attr = READ_ONCE(pid->attr); 783 784 VFS_WARN_ON_ONCE(!attr); 785 VFS_WARN_ON_ONCE(attr == PIDFS_PID_DEAD); 786 787 /* Note how we were coredumped and that we coredumped. */ 788 attr->coredump_mask = pidfs_coredump_mask(cprm->dumpable) | 789 PIDFD_COREDUMPED; 790 /* If coredumping is set to skip we should never end up here. */ 791 VFS_WARN_ON_ONCE(attr->coredump_mask & PIDFD_COREDUMP_SKIP); 792 /* Expose the signal number and code that caused the coredump. */ 793 attr->coredump_signal = cprm->siginfo->si_signo; 794 attr->coredump_code = cprm->siginfo->si_code; 795 smp_wmb(); 796 set_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask); 797 } 798 #endif 799 800 static struct vfsmount *pidfs_mnt __ro_after_init; 801 802 /* 803 * The vfs falls back to simple_setattr() if i_op->setattr() isn't 804 * implemented. Let's reject it completely until we have a clean 805 * permission concept for pidfds. 806 */ 807 static int pidfs_setattr(struct mnt_idmap *idmap, struct dentry *dentry, 808 struct iattr *attr) 809 { 810 return anon_inode_setattr(idmap, dentry, attr); 811 } 812 813 static int pidfs_getattr(struct mnt_idmap *idmap, const struct path *path, 814 struct kstat *stat, u32 request_mask, 815 unsigned int query_flags) 816 { 817 return anon_inode_getattr(idmap, path, stat, request_mask, query_flags); 818 } 819 820 static ssize_t pidfs_listxattr(struct dentry *dentry, char *buf, size_t size) 821 { 822 struct inode *inode = d_inode(dentry); 823 struct pid *pid = inode->i_private; 824 825 return simple_xattr_list(inode, &pid->attr->xattrs, buf, size); 826 } 827 828 static const struct inode_operations pidfs_inode_operations = { 829 .getattr = pidfs_getattr, 830 .setattr = pidfs_setattr, 831 .listxattr = pidfs_listxattr, 832 }; 833 834 static void pidfs_evict_inode(struct inode *inode) 835 { 836 struct pid *pid = inode->i_private; 837 838 clear_inode(inode); 839 put_pid(pid); 840 } 841 842 static const struct super_operations pidfs_sops = { 843 .drop_inode = inode_just_drop, 844 .evict_inode = pidfs_evict_inode, 845 .statfs = simple_statfs, 846 }; 847 848 /* 849 * 'lsof' has knowledge of out historical anon_inode use, and expects 850 * the pidfs dentry name to start with 'anon_inode'. 851 */ 852 static char *pidfs_dname(struct dentry *dentry, char *buffer, int buflen) 853 { 854 return dynamic_dname(buffer, buflen, "anon_inode:[pidfd]"); 855 } 856 857 const struct dentry_operations pidfs_dentry_operations = { 858 .d_dname = pidfs_dname, 859 .d_prune = stashed_dentry_prune, 860 }; 861 862 static int pidfs_encode_fh(struct inode *inode, u32 *fh, int *max_len, 863 struct inode *parent) 864 { 865 const struct pid *pid = inode->i_private; 866 867 if (*max_len < 2) { 868 *max_len = 2; 869 return FILEID_INVALID; 870 } 871 872 *max_len = 2; 873 *(u64 *)fh = pid->ino; 874 return FILEID_KERNFS; 875 } 876 877 /* Find a struct pid based on the inode number. */ 878 static struct pid *pidfs_ino_get_pid(u64 ino) 879 { 880 struct pid *pid; 881 struct pidfs_attr *attr; 882 883 guard(rcu)(); 884 pid = rhashtable_lookup(&pidfs_ino_ht, &ino, pidfs_ino_ht_params); 885 if (!pid) 886 return NULL; 887 attr = READ_ONCE(pid->attr); 888 if (IS_ERR_OR_NULL(attr)) 889 return NULL; 890 if (test_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask)) 891 return NULL; 892 /* Within our pid namespace hierarchy? */ 893 if (pid_vnr(pid) == 0) 894 return NULL; 895 return get_pid(pid); 896 } 897 898 static struct dentry *pidfs_fh_to_dentry(struct super_block *sb, 899 struct fid *fid, int fh_len, 900 int fh_type) 901 { 902 int ret; 903 u64 pid_ino; 904 struct path path; 905 struct pid *pid; 906 907 if (fh_len < 2) 908 return NULL; 909 910 switch (fh_type) { 911 case FILEID_KERNFS: 912 pid_ino = *(u64 *)fid; 913 break; 914 default: 915 return NULL; 916 } 917 918 pid = pidfs_ino_get_pid(pid_ino); 919 if (!pid) 920 return NULL; 921 922 ret = path_from_stashed(&pid->stashed, pidfs_mnt, pid, &path); 923 if (ret < 0) 924 return ERR_PTR(ret); 925 926 VFS_WARN_ON_ONCE(!pid->attr); 927 928 mntput(path.mnt); 929 return path.dentry; 930 } 931 932 static struct file *pidfs_dentry_open(const struct path *path, 933 unsigned int flags, 934 const struct cred *cred) 935 { 936 struct file *file; 937 938 /* pidfds are always O_RDWR. */ 939 file = dentry_open(path, flags | O_RDWR, cred); 940 /* do_dentry_open() strips O_EXCL and O_TRUNC. */ 941 if (!IS_ERR(file)) 942 file->f_flags |= flags & (PIDFD_THREAD | PIDFD_AUTOKILL); 943 return file; 944 } 945 946 /* 947 * Make sure that we reject any nonsensical flags that users pass via 948 * open_by_handle_at(). Note that PIDFD_THREAD is defined as O_EXCL, and 949 * PIDFD_NONBLOCK as O_NONBLOCK. 950 */ 951 #define VALID_FILE_HANDLE_OPEN_FLAGS \ 952 (O_RDONLY | O_WRONLY | O_RDWR | O_NONBLOCK | O_CLOEXEC | O_EXCL) 953 954 static int pidfs_export_permission(struct handle_to_path_ctx *ctx, 955 unsigned int oflags) 956 { 957 if (oflags & ~(VALID_FILE_HANDLE_OPEN_FLAGS | O_LARGEFILE)) 958 return -EINVAL; 959 960 /* 961 * pidfd_ino_get_pid() will verify that the struct pid is part 962 * of the caller's pid namespace hierarchy. No further 963 * permission checks are needed. 964 */ 965 return 0; 966 } 967 968 static struct file *pidfs_export_open(const struct path *path, unsigned int oflags) 969 { 970 /* 971 * Opening via file handle may never raise PIDFD_AUTOKILL. That can 972 * only be done at task creation! 973 */ 974 if (WARN_ON_ONCE(oflags & PIDFD_AUTOKILL)) 975 return ERR_PTR(-EINVAL); 976 /* Clear O_LARGEFILE as open_by_handle_at() forces it. */ 977 return pidfs_dentry_open(path, oflags & ~O_LARGEFILE, current_cred()); 978 } 979 980 static const struct export_operations pidfs_export_operations = { 981 .encode_fh = pidfs_encode_fh, 982 .fh_to_dentry = pidfs_fh_to_dentry, 983 .open = pidfs_export_open, 984 .permission = pidfs_export_permission, 985 }; 986 987 static int pidfs_init_inode(struct inode *inode, void *data) 988 { 989 const struct pid *pid = data; 990 991 inode->i_private = data; 992 inode->i_flags |= S_PRIVATE | S_ANON_INODE; 993 /* We allow to set xattrs. */ 994 inode->i_flags &= ~S_IMMUTABLE; 995 inode->i_mode |= S_IRWXU; 996 inode->i_op = &pidfs_inode_operations; 997 inode->i_fop = &pidfs_file_operations; 998 inode->i_ino = pidfs_ino(pid->ino); 999 inode->i_generation = pidfs_gen(pid->ino); 1000 return 0; 1001 } 1002 1003 static void pidfs_put_data(void *data) 1004 { 1005 struct pid *pid = data; 1006 put_pid(pid); 1007 } 1008 1009 /** 1010 * pidfs_register_pid_gfp - register a struct pid in pidfs with custom GFP 1011 * flags 1012 * @pid: pid to pin 1013 * @gfp: GFP flags for memory allocation 1014 * 1015 * Register a struct pid in pidfs with custom GFP flags. 1016 * 1017 * Return: On success zero, on error a negative error code is returned. 1018 */ 1019 int pidfs_register_pid_gfp(struct pid *pid, gfp_t gfp) 1020 { 1021 struct pidfs_attr *new_attr __free(kfree) = NULL; 1022 struct pidfs_attr *attr; 1023 1024 might_sleep(); 1025 1026 if (!pid) 1027 return 0; 1028 1029 attr = READ_ONCE(pid->attr); 1030 if (unlikely(attr == PIDFS_PID_DEAD)) 1031 return PTR_ERR(PIDFS_PID_DEAD); 1032 if (attr) 1033 return 0; 1034 1035 new_attr = kmem_cache_zalloc(pidfs_attr_cachep, gfp); 1036 if (!new_attr) 1037 return -ENOMEM; 1038 1039 INIT_LIST_HEAD_RCU(&new_attr->xattrs); 1040 1041 /* Synchronize with pidfs_exit(). */ 1042 guard(spinlock_irq)(&pid->wait_pidfd.lock); 1043 1044 attr = pid->attr; 1045 if (unlikely(attr == PIDFS_PID_DEAD)) 1046 return PTR_ERR(PIDFS_PID_DEAD); 1047 if (unlikely(attr)) 1048 return 0; 1049 1050 pid->attr = no_free_ptr(new_attr); 1051 return 0; 1052 } 1053 1054 static struct dentry *pidfs_stash_dentry(struct dentry **stashed, 1055 struct dentry *dentry) 1056 { 1057 int ret; 1058 struct pid *pid = d_inode(dentry)->i_private; 1059 1060 VFS_WARN_ON_ONCE(stashed != &pid->stashed); 1061 1062 ret = pidfs_register_pid(pid); 1063 if (ret) 1064 return ERR_PTR(ret); 1065 1066 return stash_dentry(stashed, dentry); 1067 } 1068 1069 static const struct stashed_operations pidfs_stashed_ops = { 1070 .stash_dentry = pidfs_stash_dentry, 1071 .init_inode = pidfs_init_inode, 1072 .put_data = pidfs_put_data, 1073 }; 1074 1075 static int pidfs_xattr_get(const struct xattr_handler *handler, 1076 struct dentry *unused, struct inode *inode, 1077 const char *suffix, void *value, size_t size) 1078 { 1079 struct pid *pid = inode->i_private; 1080 const char *name = xattr_full_name(handler, suffix); 1081 1082 return simple_xattr_get(&pidfs_xa_cache, &pid->attr->xattrs, name, value, size); 1083 } 1084 1085 static int pidfs_xattr_set(const struct xattr_handler *handler, 1086 struct mnt_idmap *idmap, struct dentry *unused, 1087 struct inode *inode, const char *suffix, 1088 const void *value, size_t size, int flags) 1089 { 1090 struct pid *pid = inode->i_private; 1091 const char *name = xattr_full_name(handler, suffix); 1092 struct simple_xattr *old_xattr; 1093 1094 /* Ensure we're the only one to set @attr->xattrs. */ 1095 WARN_ON_ONCE(!inode_is_locked(inode)); 1096 1097 old_xattr = simple_xattr_set(&pidfs_xa_cache, &pid->attr->xattrs, name, value, size, flags); 1098 if (IS_ERR(old_xattr)) 1099 return PTR_ERR(old_xattr); 1100 1101 simple_xattr_free_rcu(old_xattr); 1102 return 0; 1103 } 1104 1105 static const struct xattr_handler pidfs_trusted_xattr_handler = { 1106 .prefix = XATTR_TRUSTED_PREFIX, 1107 .get = pidfs_xattr_get, 1108 .set = pidfs_xattr_set, 1109 }; 1110 1111 static const struct xattr_handler *const pidfs_xattr_handlers[] = { 1112 &pidfs_trusted_xattr_handler, 1113 NULL 1114 }; 1115 1116 static int pidfs_init_fs_context(struct fs_context *fc) 1117 { 1118 struct pseudo_fs_context *ctx; 1119 1120 ctx = init_pseudo(fc, PID_FS_MAGIC); 1121 if (!ctx) 1122 return -ENOMEM; 1123 1124 ctx->s_d_flags |= DCACHE_DONTCACHE; 1125 ctx->ops = &pidfs_sops; 1126 ctx->eops = &pidfs_export_operations; 1127 ctx->dops = &pidfs_dentry_operations; 1128 ctx->xattr = pidfs_xattr_handlers; 1129 fc->s_fs_info = (void *)&pidfs_stashed_ops; 1130 return 0; 1131 } 1132 1133 static struct file_system_type pidfs_type = { 1134 .name = "pidfs", 1135 .init_fs_context = pidfs_init_fs_context, 1136 .kill_sb = kill_anon_super, 1137 }; 1138 1139 struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags) 1140 { 1141 struct path path __free(path_put) = {}; 1142 int ret; 1143 1144 /* 1145 * Ensure that internal pidfd flags don't overlap with each 1146 * other or with uapi pidfd flags. 1147 */ 1148 BUILD_BUG_ON(hweight32(PIDFD_THREAD | PIDFD_NONBLOCK | 1149 PIDFD_STALE | PIDFD_AUTOKILL) != 4); 1150 1151 ret = path_from_stashed(&pid->stashed, pidfs_mnt, get_pid(pid), &path); 1152 if (ret < 0) 1153 return ERR_PTR(ret); 1154 1155 VFS_WARN_ON_ONCE(!pid->attr); 1156 1157 flags &= ~PIDFD_STALE; 1158 return pidfs_dentry_open(&path, flags, current_cred()); 1159 } 1160 1161 void __init pidfs_init(void) 1162 { 1163 if (rhashtable_init(&pidfs_ino_ht, &pidfs_ino_ht_params)) 1164 panic("Failed to initialize pidfs hashtable"); 1165 1166 pidfs_attr_cachep = kmem_cache_create("pidfs_attr_cache", sizeof(struct pidfs_attr), 0, 1167 (SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT | 1168 SLAB_ACCOUNT | SLAB_PANIC), NULL); 1169 1170 pidfs_mnt = kern_mount(&pidfs_type); 1171 if (IS_ERR(pidfs_mnt)) 1172 panic("Failed to mount pidfs pseudo filesystem"); 1173 1174 pidfs_root_path.mnt = pidfs_mnt; 1175 pidfs_root_path.dentry = pidfs_mnt->mnt_root; 1176 } 1177