1 /* 2 * Copyright (c) 1982, 1986, 1989, 1991, 1993 3 * The Regents of the University of California. All rights reserved. 4 * (c) UNIX System Laboratories, Inc. 5 * All or some portions of this file are derived from material licensed 6 * to the University of California by American Telephone and Telegraph 7 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 8 * the permission of UNIX System Laboratories, Inc. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94 39 * $FreeBSD: src/sys/kern/kern_fork.c,v 1.72.2.14 2003/06/26 04:15:10 silby Exp $ 40 * $DragonFly: src/sys/kern/kern_fork.c,v 1.32 2005/01/31 22:29:59 joerg Exp $ 41 */ 42 43 #include "opt_ktrace.h" 44 45 #include <sys/param.h> 46 #include <sys/systm.h> 47 #include <sys/sysproto.h> 48 #include <sys/filedesc.h> 49 #include <sys/kernel.h> 50 #include <sys/sysctl.h> 51 #include <sys/malloc.h> 52 #include <sys/proc.h> 53 #include <sys/resourcevar.h> 54 #include <sys/vnode.h> 55 #include <sys/acct.h> 56 #include <sys/ktrace.h> 57 #include <sys/unistd.h> 58 #include <sys/jail.h> 59 #include <sys/caps.h> 60 61 #include <vm/vm.h> 62 #include <sys/lock.h> 63 #include <vm/pmap.h> 64 #include <vm/vm_map.h> 65 #include <vm/vm_extern.h> 66 #include <vm/vm_zone.h> 67 68 #include <sys/vmmeter.h> 69 #include <sys/user.h> 70 71 static MALLOC_DEFINE(M_ATFORK, "atfork", "atfork callback"); 72 73 /* 74 * These are the stuctures used to create a callout list for things to do 75 * when forking a process 76 */ 77 struct forklist { 78 forklist_fn function; 79 TAILQ_ENTRY(forklist) next; 80 }; 81 82 TAILQ_HEAD(forklist_head, forklist); 83 static struct forklist_head fork_list = TAILQ_HEAD_INITIALIZER(fork_list); 84 85 int forksleep; /* Place for fork1() to sleep on. */ 86 87 /* ARGSUSED */ 88 int 89 fork(struct fork_args *uap) 90 { 91 struct proc *p = curproc; 92 struct proc *p2; 93 int error; 94 95 error = fork1(p, RFFDG | RFPROC, &p2); 96 if (error == 0) { 97 start_forked_proc(p, p2); 98 uap->sysmsg_fds[0] = p2->p_pid; 99 uap->sysmsg_fds[1] = 0; 100 } 101 return error; 102 } 103 104 /* ARGSUSED */ 105 int 106 vfork(struct vfork_args *uap) 107 { 108 struct proc *p = curproc; 109 struct proc *p2; 110 int error; 111 112 error = fork1(p, RFFDG | RFPROC | RFPPWAIT | RFMEM, &p2); 113 if (error == 0) { 114 start_forked_proc(p, p2); 115 uap->sysmsg_fds[0] = p2->p_pid; 116 uap->sysmsg_fds[1] = 0; 117 } 118 return error; 119 } 120 121 /* 122 * Handle rforks. An rfork may (1) operate on the current process without 123 * creating a new, (2) create a new process that shared the current process's 124 * vmspace, signals, and/or descriptors, or (3) create a new process that does 125 * not share these things (normal fork). 126 * 127 * Note that we only call start_forked_proc() if a new process is actually 128 * created. 129 * 130 * rfork { int flags } 131 */ 132 int 133 rfork(struct rfork_args *uap) 134 { 135 struct proc *p = curproc; 136 struct proc *p2; 137 int error; 138 139 if ((uap->flags & RFKERNELONLY) != 0) 140 return (EINVAL); 141 142 error = fork1(p, uap->flags, &p2); 143 if (error == 0) { 144 if (p2) 145 start_forked_proc(p, p2); 146 uap->sysmsg_fds[0] = p2 ? p2->p_pid : 0; 147 uap->sysmsg_fds[1] = 0; 148 } 149 return error; 150 } 151 152 153 int nprocs = 1; /* process 0 */ 154 static int nextpid = 0; 155 156 /* 157 * Random component to nextpid generation. We mix in a random factor to make 158 * it a little harder to predict. We sanity check the modulus value to avoid 159 * doing it in critical paths. Don't let it be too small or we pointlessly 160 * waste randomness entropy, and don't let it be impossibly large. Using a 161 * modulus that is too big causes a LOT more process table scans and slows 162 * down fork processing as the pidchecked caching is defeated. 163 */ 164 static int randompid = 0; 165 166 static int 167 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS) 168 { 169 int error, pid; 170 171 pid = randompid; 172 error = sysctl_handle_int(oidp, &pid, 0, req); 173 if (error || !req->newptr) 174 return (error); 175 if (pid < 0 || pid > PID_MAX - 100) /* out of range */ 176 pid = PID_MAX - 100; 177 else if (pid < 2) /* NOP */ 178 pid = 0; 179 else if (pid < 100) /* Make it reasonable */ 180 pid = 100; 181 randompid = pid; 182 return (error); 183 } 184 185 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW, 186 0, 0, sysctl_kern_randompid, "I", "Random PID modulus"); 187 188 int 189 fork1(struct proc *p1, int flags, struct proc **procp) 190 { 191 struct proc *p2, *pptr; 192 uid_t uid; 193 struct proc *newproc; 194 int ok; 195 static int curfail = 0, pidchecked = 0; 196 static struct timeval lastfail; 197 struct forklist *ep; 198 struct filedesc_to_leader *fdtol; 199 200 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG)) 201 return (EINVAL); 202 203 /* 204 * Here we don't create a new process, but we divorce 205 * certain parts of a process from itself. 206 */ 207 if ((flags & RFPROC) == 0) { 208 209 vm_fork(p1, 0, flags); 210 211 /* 212 * Close all file descriptors. 213 */ 214 if (flags & RFCFDG) { 215 struct filedesc *fdtmp; 216 fdtmp = fdinit(p1); 217 fdfree(p1); 218 p1->p_fd = fdtmp; 219 } 220 221 /* 222 * Unshare file descriptors (from parent.) 223 */ 224 if (flags & RFFDG) { 225 if (p1->p_fd->fd_refcnt > 1) { 226 struct filedesc *newfd; 227 newfd = fdcopy(p1); 228 fdfree(p1); 229 p1->p_fd = newfd; 230 } 231 } 232 *procp = NULL; 233 return (0); 234 } 235 236 /* 237 * Although process entries are dynamically created, we still keep 238 * a global limit on the maximum number we will create. Don't allow 239 * a nonprivileged user to use the last ten processes; don't let root 240 * exceed the limit. The variable nprocs is the current number of 241 * processes, maxproc is the limit. 242 */ 243 uid = p1->p_ucred->cr_ruid; 244 if ((nprocs >= maxproc - 10 && uid != 0) || nprocs >= maxproc) { 245 if (ppsratecheck(&lastfail, &curfail, 1)) 246 printf("maxproc limit exceeded by uid %d, please " 247 "see tuning(7) and login.conf(5).\n", uid); 248 tsleep(&forksleep, 0, "fork", hz / 2); 249 return (EAGAIN); 250 } 251 /* 252 * Increment the nprocs resource before blocking can occur. There 253 * are hard-limits as to the number of processes that can run. 254 */ 255 nprocs++; 256 257 /* 258 * Increment the count of procs running with this uid. Don't allow 259 * a nonprivileged user to exceed their current limit. 260 */ 261 ok = chgproccnt(p1->p_ucred->cr_ruidinfo, 1, 262 (uid != 0) ? p1->p_rlimit[RLIMIT_NPROC].rlim_cur : 0); 263 if (!ok) { 264 /* 265 * Back out the process count 266 */ 267 nprocs--; 268 if (ppsratecheck(&lastfail, &curfail, 1)) 269 printf("maxproc limit exceeded by uid %d, please " 270 "see tuning(7) and login.conf(5).\n", uid); 271 tsleep(&forksleep, 0, "fork", hz / 2); 272 return (EAGAIN); 273 } 274 275 /* Allocate new proc. */ 276 newproc = zalloc(proc_zone); 277 278 /* 279 * Setup linkage for kernel based threading 280 */ 281 if ((flags & RFTHREAD) != 0) { 282 newproc->p_peers = p1->p_peers; 283 p1->p_peers = newproc; 284 newproc->p_leader = p1->p_leader; 285 } else { 286 newproc->p_peers = 0; 287 newproc->p_leader = newproc; 288 } 289 290 newproc->p_wakeup = 0; 291 newproc->p_vmspace = NULL; 292 TAILQ_INIT(&newproc->p_sysmsgq); 293 294 /* 295 * Find an unused process ID. We remember a range of unused IDs 296 * ready to use (from nextpid+1 through pidchecked-1). 297 */ 298 nextpid++; 299 if (randompid) 300 nextpid += arc4random() % randompid; 301 retry: 302 /* 303 * If the process ID prototype has wrapped around, 304 * restart somewhat above 0, as the low-numbered procs 305 * tend to include daemons that don't exit. 306 */ 307 if (nextpid >= PID_MAX) { 308 nextpid = nextpid % PID_MAX; 309 if (nextpid < 100) 310 nextpid += 100; 311 pidchecked = 0; 312 } 313 if (nextpid >= pidchecked) { 314 int doingzomb = 0; 315 316 pidchecked = PID_MAX; 317 /* 318 * Scan the active and zombie procs to check whether this pid 319 * is in use. Remember the lowest pid that's greater 320 * than nextpid, so we can avoid checking for a while. 321 */ 322 p2 = LIST_FIRST(&allproc); 323 again: 324 for (; p2 != 0; p2 = LIST_NEXT(p2, p_list)) { 325 while (p2->p_pid == nextpid || 326 p2->p_pgrp->pg_id == nextpid || 327 p2->p_session->s_sid == nextpid) { 328 nextpid++; 329 if (nextpid >= pidchecked) 330 goto retry; 331 } 332 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 333 pidchecked = p2->p_pid; 334 if (p2->p_pgrp->pg_id > nextpid && 335 pidchecked > p2->p_pgrp->pg_id) 336 pidchecked = p2->p_pgrp->pg_id; 337 if (p2->p_session->s_sid > nextpid && 338 pidchecked > p2->p_session->s_sid) 339 pidchecked = p2->p_session->s_sid; 340 } 341 if (!doingzomb) { 342 doingzomb = 1; 343 p2 = LIST_FIRST(&zombproc); 344 goto again; 345 } 346 } 347 348 p2 = newproc; 349 p2->p_stat = SIDL; /* protect against others */ 350 p2->p_pid = nextpid; 351 LIST_INSERT_HEAD(&allproc, p2, p_list); 352 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 353 354 /* 355 * Make a proc table entry for the new process. 356 * Start by zeroing the section of proc that is zero-initialized, 357 * then copy the section that is copied directly from the parent. 358 */ 359 bzero(&p2->p_startzero, 360 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 361 bcopy(&p1->p_startcopy, &p2->p_startcopy, 362 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 363 364 p2->p_aioinfo = NULL; 365 366 /* 367 * Duplicate sub-structures as needed. 368 * Increase reference counts on shared objects. 369 * The p_stats and p_sigacts substructs are set in vm_fork. 370 */ 371 p2->p_flag = P_INMEM; 372 if (p1->p_flag & P_PROFIL) 373 startprofclock(p2); 374 p2->p_ucred = crhold(p1->p_ucred); 375 376 if (jailed(p2->p_ucred)) 377 p2->p_flag |= P_JAILED; 378 379 if (p2->p_args) 380 p2->p_args->ar_ref++; 381 382 if (flags & RFSIGSHARE) { 383 p2->p_procsig = p1->p_procsig; 384 p2->p_procsig->ps_refcnt++; 385 if (p1->p_sigacts == &p1->p_addr->u_sigacts) { 386 struct sigacts *newsigacts; 387 int s; 388 389 /* Create the shared sigacts structure */ 390 MALLOC(newsigacts, struct sigacts *, 391 sizeof(struct sigacts), M_SUBPROC, M_WAITOK); 392 s = splhigh(); 393 /* 394 * Set p_sigacts to the new shared structure. 395 * Note that this is updating p1->p_sigacts at the 396 * same time, since p_sigacts is just a pointer to 397 * the shared p_procsig->ps_sigacts. 398 */ 399 p2->p_sigacts = newsigacts; 400 bcopy(&p1->p_addr->u_sigacts, p2->p_sigacts, 401 sizeof(*p2->p_sigacts)); 402 *p2->p_sigacts = p1->p_addr->u_sigacts; 403 splx(s); 404 } 405 } else { 406 MALLOC(p2->p_procsig, struct procsig *, sizeof(struct procsig), 407 M_SUBPROC, M_WAITOK); 408 bcopy(p1->p_procsig, p2->p_procsig, sizeof(*p2->p_procsig)); 409 p2->p_procsig->ps_refcnt = 1; 410 p2->p_sigacts = NULL; /* finished in vm_fork() */ 411 } 412 if (flags & RFLINUXTHPN) 413 p2->p_sigparent = SIGUSR1; 414 else 415 p2->p_sigparent = SIGCHLD; 416 417 /* bump references to the text vnode (for procfs) */ 418 p2->p_textvp = p1->p_textvp; 419 if (p2->p_textvp) 420 vref(p2->p_textvp); 421 422 if (flags & RFCFDG) { 423 p2->p_fd = fdinit(p1); 424 fdtol = NULL; 425 } else if (flags & RFFDG) { 426 p2->p_fd = fdcopy(p1); 427 fdtol = NULL; 428 } else { 429 p2->p_fd = fdshare(p1); 430 if (p1->p_fdtol == NULL) 431 p1->p_fdtol = 432 filedesc_to_leader_alloc(NULL, 433 p1->p_leader); 434 if ((flags & RFTHREAD) != 0) { 435 /* 436 * Shared file descriptor table and 437 * shared process leaders. 438 */ 439 fdtol = p1->p_fdtol; 440 fdtol->fdl_refcount++; 441 } else { 442 /* 443 * Shared file descriptor table, and 444 * different process leaders 445 */ 446 fdtol = filedesc_to_leader_alloc(p1->p_fdtol, p2); 447 } 448 } 449 p2->p_fdtol = fdtol; 450 451 /* 452 * If p_limit is still copy-on-write, bump refcnt, 453 * otherwise get a copy that won't be modified. 454 * (If PL_SHAREMOD is clear, the structure is shared 455 * copy-on-write.) 456 */ 457 if (p1->p_limit->p_lflags & PL_SHAREMOD) { 458 p2->p_limit = limcopy(p1->p_limit); 459 } else { 460 p2->p_limit = p1->p_limit; 461 p2->p_limit->p_refcnt++; 462 } 463 464 /* 465 * Preserve some more flags in subprocess. P_PROFIL has already 466 * been preserved. 467 */ 468 p2->p_flag |= p1->p_flag & (P_SUGID | P_ALTSTACK); 469 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 470 p2->p_flag |= P_CONTROLT; 471 if (flags & RFPPWAIT) 472 p2->p_flag |= P_PPWAIT; 473 474 /* 475 * Once we are on a pglist we may receive signals. XXX we might 476 * race a ^C being sent to the process group by not receiving it 477 * at all prior to this line. 478 */ 479 LIST_INSERT_AFTER(p1, p2, p_pglist); 480 481 /* 482 * Attach the new process to its parent. 483 * 484 * If RFNOWAIT is set, the newly created process becomes a child 485 * of init. This effectively disassociates the child from the 486 * parent. 487 */ 488 if (flags & RFNOWAIT) 489 pptr = initproc; 490 else 491 pptr = p1; 492 p2->p_pptr = pptr; 493 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling); 494 LIST_INIT(&p2->p_children); 495 varsymset_init(&p2->p_varsymset, &p1->p_varsymset); 496 callout_init(&p2->p_ithandle); 497 498 #ifdef KTRACE 499 /* 500 * Copy traceflag and tracefile if enabled. If not inherited, 501 * these were zeroed above but we still could have a trace race 502 * so make sure p2's p_tracep is NULL. 503 */ 504 if ((p1->p_traceflag & KTRFAC_INHERIT) && p2->p_tracep == NULL) { 505 p2->p_traceflag = p1->p_traceflag; 506 if ((p2->p_tracep = p1->p_tracep) != NULL) 507 vref(p2->p_tracep); 508 } 509 #endif 510 511 /* 512 * Give the child process an estcpu skewed towards the batch side 513 * of the parent. This prevents batch programs from glitching 514 * interactive programs when they are first started. If the child 515 * is not a batch program it's priority will be corrected by the 516 * scheduler. 517 * 518 * The interactivity model always starts at 0 (par value). 519 */ 520 p2->p_estcpu_fork = p2->p_estcpu = 521 ESTCPULIM(p1->p_estcpu + ESTCPURAMP); 522 p2->p_interactive = 0; 523 524 /* 525 * This begins the section where we must prevent the parent 526 * from being swapped. 527 */ 528 PHOLD(p1); 529 530 /* 531 * Finish creating the child process. It will return via a different 532 * execution path later. (ie: directly into user mode) 533 */ 534 vm_fork(p1, p2, flags); 535 caps_fork(p1, p2, flags); 536 537 if (flags == (RFFDG | RFPROC)) { 538 mycpu->gd_cnt.v_forks++; 539 mycpu->gd_cnt.v_forkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 540 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) { 541 mycpu->gd_cnt.v_vforks++; 542 mycpu->gd_cnt.v_vforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 543 } else if (p1 == &proc0) { 544 mycpu->gd_cnt.v_kthreads++; 545 mycpu->gd_cnt.v_kthreadpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 546 } else { 547 mycpu->gd_cnt.v_rforks++; 548 mycpu->gd_cnt.v_rforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 549 } 550 551 /* 552 * Both processes are set up, now check if any loadable modules want 553 * to adjust anything. 554 * What if they have an error? XXX 555 */ 556 TAILQ_FOREACH(ep, &fork_list, next) { 557 (*ep->function)(p1, p2, flags); 558 } 559 560 /* 561 * Make child runnable and add to run queue. 562 */ 563 microtime(&p2->p_thread->td_start); 564 p2->p_acflag = AFORK; 565 566 /* 567 * tell any interested parties about the new process 568 */ 569 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid); 570 571 /* 572 * Return child proc pointer to parent. 573 */ 574 *procp = p2; 575 return (0); 576 } 577 578 /* 579 * The next two functionms are general routines to handle adding/deleting 580 * items on the fork callout list. 581 * 582 * at_fork(): 583 * Take the arguments given and put them onto the fork callout list, 584 * However first make sure that it's not already there. 585 * Returns 0 on success or a standard error number. 586 */ 587 int 588 at_fork(forklist_fn function) 589 { 590 struct forklist *ep; 591 592 #ifdef INVARIANTS 593 /* let the programmer know if he's been stupid */ 594 if (rm_at_fork(function)) { 595 printf("WARNING: fork callout entry (%p) already present\n", 596 function); 597 } 598 #endif 599 ep = malloc(sizeof(*ep), M_ATFORK, M_WAITOK|M_ZERO); 600 ep->function = function; 601 TAILQ_INSERT_TAIL(&fork_list, ep, next); 602 return (0); 603 } 604 605 /* 606 * Scan the exit callout list for the given item and remove it.. 607 * Returns the number of items removed (0 or 1) 608 */ 609 int 610 rm_at_fork(forklist_fn function) 611 { 612 struct forklist *ep; 613 614 TAILQ_FOREACH(ep, &fork_list, next) { 615 if (ep->function == function) { 616 TAILQ_REMOVE(&fork_list, ep, next); 617 free(ep, M_ATFORK); 618 return(1); 619 } 620 } 621 return (0); 622 } 623 624 /* 625 * Add a forked process to the run queue after any remaining setup, such 626 * as setting the fork handler, has been completed. 627 */ 628 void 629 start_forked_proc(struct proc *p1, struct proc *p2) 630 { 631 /* 632 * Move from SIDL to RUN queue, and activate the process's thread. 633 * Activation of the thread effectively makes the process "a" 634 * current process, so we do not setrunqueue(). 635 * 636 * YYY setrunqueue works here but we should clean up the trampoline 637 * code so we just schedule the LWKT thread and let the trampoline 638 * deal with the userland scheduler on return to userland. 639 */ 640 KASSERT(p2 && p2->p_stat == SIDL, 641 ("cannot start forked process, bad status: %p", p2)); 642 resetpriority(p2); 643 (void) splhigh(); 644 p2->p_stat = SRUN; 645 setrunqueue(p2); 646 (void) spl0(); 647 648 /* 649 * Now can be swapped. 650 */ 651 PRELE(p1); 652 653 /* 654 * Preserve synchronization semantics of vfork. If waiting for 655 * child to exec or exit, set P_PPWAIT on child, and sleep on our 656 * proc (in case of exit). 657 */ 658 while (p2->p_flag & P_PPWAIT) 659 tsleep(p1, 0, "ppwait", 0); 660 } 661 662