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 1.72.2.13 2003/06/06 20:21:32 tegge Exp $ 40 * $DragonFly: src/sys/kern/kern_fork.c,v 1.16 2003/11/05 23:26:20 dillon 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 60 #include <vm/vm.h> 61 #include <sys/lock.h> 62 #include <vm/pmap.h> 63 #include <vm/vm_map.h> 64 #include <vm/vm_extern.h> 65 #include <vm/vm_zone.h> 66 67 #include <sys/vmmeter.h> 68 #include <sys/user.h> 69 70 static MALLOC_DEFINE(M_ATFORK, "atfork", "atfork callback"); 71 72 /* 73 * These are the stuctures used to create a callout list for things to do 74 * when forking a process 75 */ 76 struct forklist { 77 forklist_fn function; 78 TAILQ_ENTRY(forklist) next; 79 }; 80 81 TAILQ_HEAD(forklist_head, forklist); 82 static struct forklist_head fork_list = TAILQ_HEAD_INITIALIZER(fork_list); 83 84 int forksleep; /* Place for fork1() to sleep on. */ 85 86 /* ARGSUSED */ 87 int 88 fork(struct fork_args *uap) 89 { 90 struct proc *p = curproc; 91 struct proc *p2; 92 int error; 93 94 error = fork1(p, RFFDG | RFPROC, &p2); 95 if (error == 0) { 96 start_forked_proc(p, p2); 97 uap->sysmsg_fds[0] = p2->p_pid; 98 uap->sysmsg_fds[1] = 0; 99 } 100 return error; 101 } 102 103 /* ARGSUSED */ 104 int 105 vfork(struct vfork_args *uap) 106 { 107 struct proc *p = curproc; 108 struct proc *p2; 109 int error; 110 111 error = fork1(p, RFFDG | RFPROC | RFPPWAIT | RFMEM, &p2); 112 if (error == 0) { 113 start_forked_proc(p, p2); 114 uap->sysmsg_fds[0] = p2->p_pid; 115 uap->sysmsg_fds[1] = 0; 116 } 117 return error; 118 } 119 120 int 121 rfork(struct rfork_args *uap) 122 { 123 struct proc *p = curproc; 124 struct proc *p2; 125 int error; 126 127 error = fork1(p, uap->flags, &p2); 128 if (error == 0) { 129 start_forked_proc(p, p2); 130 uap->sysmsg_fds[0] = p2 ? p2->p_pid : 0; 131 uap->sysmsg_fds[1] = 0; 132 } 133 return error; 134 } 135 136 137 int nprocs = 1; /* process 0 */ 138 static int nextpid = 0; 139 140 /* 141 * Random component to nextpid generation. We mix in a random factor to make 142 * it a little harder to predict. We sanity check the modulus value to avoid 143 * doing it in critical paths. Don't let it be too small or we pointlessly 144 * waste randomness entropy, and don't let it be impossibly large. Using a 145 * modulus that is too big causes a LOT more process table scans and slows 146 * down fork processing as the pidchecked caching is defeated. 147 */ 148 static int randompid = 0; 149 150 static int 151 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS) 152 { 153 int error, pid; 154 155 pid = randompid; 156 error = sysctl_handle_int(oidp, &pid, 0, req); 157 if (error || !req->newptr) 158 return (error); 159 if (pid < 0 || pid > PID_MAX - 100) /* out of range */ 160 pid = PID_MAX - 100; 161 else if (pid < 2) /* NOP */ 162 pid = 0; 163 else if (pid < 100) /* Make it reasonable */ 164 pid = 100; 165 randompid = pid; 166 return (error); 167 } 168 169 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW, 170 0, 0, sysctl_kern_randompid, "I", "Random PID modulus"); 171 172 int 173 fork1(p1, flags, procp) 174 struct proc *p1; 175 int flags; 176 struct proc **procp; 177 { 178 struct proc *p2, *pptr; 179 uid_t uid; 180 struct proc *newproc; 181 int ok; 182 static int pidchecked = 0; 183 struct forklist *ep; 184 struct filedesc_to_leader *fdtol; 185 186 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG)) 187 return (EINVAL); 188 189 /* 190 * Here we don't create a new process, but we divorce 191 * certain parts of a process from itself. 192 */ 193 if ((flags & RFPROC) == 0) { 194 195 vm_fork(p1, 0, flags); 196 197 /* 198 * Close all file descriptors. 199 */ 200 if (flags & RFCFDG) { 201 struct filedesc *fdtmp; 202 fdtmp = fdinit(p1); 203 fdfree(p1); 204 p1->p_fd = fdtmp; 205 } 206 207 /* 208 * Unshare file descriptors (from parent.) 209 */ 210 if (flags & RFFDG) { 211 if (p1->p_fd->fd_refcnt > 1) { 212 struct filedesc *newfd; 213 newfd = fdcopy(p1); 214 fdfree(p1); 215 p1->p_fd = newfd; 216 } 217 } 218 *procp = NULL; 219 return (0); 220 } 221 222 /* 223 * Although process entries are dynamically created, we still keep 224 * a global limit on the maximum number we will create. Don't allow 225 * a nonprivileged user to use the last ten processes; don't let root 226 * exceed the limit. The variable nprocs is the current number of 227 * processes, maxproc is the limit. 228 */ 229 uid = p1->p_ucred->cr_ruid; 230 if ((nprocs >= maxproc - 10 && uid != 0) || nprocs >= maxproc) { 231 tsleep(&forksleep, 0, "fork", hz / 2); 232 return (EAGAIN); 233 } 234 /* 235 * Increment the nprocs resource before blocking can occur. There 236 * are hard-limits as to the number of processes that can run. 237 */ 238 nprocs++; 239 240 /* 241 * Increment the count of procs running with this uid. Don't allow 242 * a nonprivileged user to exceed their current limit. 243 */ 244 ok = chgproccnt(p1->p_ucred->cr_ruidinfo, 1, 245 (uid != 0) ? p1->p_rlimit[RLIMIT_NPROC].rlim_cur : 0); 246 if (!ok) { 247 /* 248 * Back out the process count 249 */ 250 nprocs--; 251 tsleep(&forksleep, 0, "fork", hz / 2); 252 return (EAGAIN); 253 } 254 255 /* Allocate new proc. */ 256 newproc = zalloc(proc_zone); 257 258 /* 259 * Setup linkage for kernel based threading 260 */ 261 if((flags & RFTHREAD) != 0) { 262 newproc->p_peers = p1->p_peers; 263 p1->p_peers = newproc; 264 newproc->p_leader = p1->p_leader; 265 } else { 266 newproc->p_peers = 0; 267 newproc->p_leader = newproc; 268 } 269 270 newproc->p_wakeup = 0; 271 newproc->p_vmspace = NULL; 272 273 /* 274 * Find an unused process ID. We remember a range of unused IDs 275 * ready to use (from nextpid+1 through pidchecked-1). 276 */ 277 nextpid++; 278 if (randompid) 279 nextpid += arc4random() % randompid; 280 retry: 281 /* 282 * If the process ID prototype has wrapped around, 283 * restart somewhat above 0, as the low-numbered procs 284 * tend to include daemons that don't exit. 285 */ 286 if (nextpid >= PID_MAX) { 287 nextpid = nextpid % PID_MAX; 288 if (nextpid < 100) 289 nextpid += 100; 290 pidchecked = 0; 291 } 292 if (nextpid >= pidchecked) { 293 int doingzomb = 0; 294 295 pidchecked = PID_MAX; 296 /* 297 * Scan the active and zombie procs to check whether this pid 298 * is in use. Remember the lowest pid that's greater 299 * than nextpid, so we can avoid checking for a while. 300 */ 301 p2 = LIST_FIRST(&allproc); 302 again: 303 for (; p2 != 0; p2 = LIST_NEXT(p2, p_list)) { 304 while (p2->p_pid == nextpid || 305 p2->p_pgrp->pg_id == nextpid || 306 p2->p_session->s_sid == nextpid) { 307 nextpid++; 308 if (nextpid >= pidchecked) 309 goto retry; 310 } 311 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 312 pidchecked = p2->p_pid; 313 if (p2->p_pgrp->pg_id > nextpid && 314 pidchecked > p2->p_pgrp->pg_id) 315 pidchecked = p2->p_pgrp->pg_id; 316 if (p2->p_session->s_sid > nextpid && 317 pidchecked > p2->p_session->s_sid) 318 pidchecked = p2->p_session->s_sid; 319 } 320 if (!doingzomb) { 321 doingzomb = 1; 322 p2 = LIST_FIRST(&zombproc); 323 goto again; 324 } 325 } 326 327 p2 = newproc; 328 p2->p_stat = SIDL; /* protect against others */ 329 p2->p_pid = nextpid; 330 LIST_INSERT_HEAD(&allproc, p2, p_list); 331 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 332 333 /* 334 * Make a proc table entry for the new process. 335 * Start by zeroing the section of proc that is zero-initialized, 336 * then copy the section that is copied directly from the parent. 337 */ 338 bzero(&p2->p_startzero, 339 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 340 bcopy(&p1->p_startcopy, &p2->p_startcopy, 341 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 342 343 p2->p_aioinfo = NULL; 344 345 /* 346 * Duplicate sub-structures as needed. 347 * Increase reference counts on shared objects. 348 * The p_stats and p_sigacts substructs are set in vm_fork. 349 * 350 * P_CP_RELEASED indicates that the process is starting out in 351 * the kernel (in the fork trampoline). The flag will be converted 352 * to P_CURPROC when the new process calls userret() and attempts 353 * to return to userland 354 */ 355 p2->p_flag = P_INMEM | P_CP_RELEASED; 356 if (p1->p_flag & P_PROFIL) 357 startprofclock(p2); 358 p2->p_ucred = crhold(p1->p_ucred); 359 360 if (p2->p_ucred->cr_prison) { 361 p2->p_ucred->cr_prison->pr_ref++; 362 p2->p_flag |= P_JAILED; 363 } 364 365 if (p2->p_args) 366 p2->p_args->ar_ref++; 367 368 if (flags & RFSIGSHARE) { 369 p2->p_procsig = p1->p_procsig; 370 p2->p_procsig->ps_refcnt++; 371 if (p1->p_sigacts == &p1->p_addr->u_sigacts) { 372 struct sigacts *newsigacts; 373 int s; 374 375 /* Create the shared sigacts structure */ 376 MALLOC(newsigacts, struct sigacts *, 377 sizeof(struct sigacts), M_SUBPROC, M_WAITOK); 378 s = splhigh(); 379 /* 380 * Set p_sigacts to the new shared structure. 381 * Note that this is updating p1->p_sigacts at the 382 * same time, since p_sigacts is just a pointer to 383 * the shared p_procsig->ps_sigacts. 384 */ 385 p2->p_sigacts = newsigacts; 386 bcopy(&p1->p_addr->u_sigacts, p2->p_sigacts, 387 sizeof(*p2->p_sigacts)); 388 *p2->p_sigacts = p1->p_addr->u_sigacts; 389 splx(s); 390 } 391 } else { 392 MALLOC(p2->p_procsig, struct procsig *, sizeof(struct procsig), 393 M_SUBPROC, M_WAITOK); 394 bcopy(p1->p_procsig, p2->p_procsig, sizeof(*p2->p_procsig)); 395 p2->p_procsig->ps_refcnt = 1; 396 p2->p_sigacts = NULL; /* finished in vm_fork() */ 397 } 398 if (flags & RFLINUXTHPN) 399 p2->p_sigparent = SIGUSR1; 400 else 401 p2->p_sigparent = SIGCHLD; 402 403 /* bump references to the text vnode (for procfs) */ 404 p2->p_textvp = p1->p_textvp; 405 if (p2->p_textvp) 406 VREF(p2->p_textvp); 407 408 if (flags & RFCFDG) { 409 p2->p_fd = fdinit(p1); 410 fdtol = NULL; 411 } else if (flags & RFFDG) { 412 p2->p_fd = fdcopy(p1); 413 fdtol = NULL; 414 } else { 415 p2->p_fd = fdshare(p1); 416 if (p1->p_fdtol == NULL) 417 p1->p_fdtol = 418 filedesc_to_leader_alloc(NULL, 419 p1->p_leader); 420 if ((flags & RFTHREAD) != 0) { 421 /* 422 * Shared file descriptor table and 423 * shared process leaders. 424 */ 425 fdtol = p1->p_fdtol; 426 fdtol->fdl_refcount++; 427 } else { 428 /* 429 * Shared file descriptor table, and 430 * different process leaders 431 */ 432 fdtol = filedesc_to_leader_alloc(p1->p_fdtol, p2); 433 } 434 } 435 p2->p_fdtol = fdtol; 436 437 /* 438 * If p_limit is still copy-on-write, bump refcnt, 439 * otherwise get a copy that won't be modified. 440 * (If PL_SHAREMOD is clear, the structure is shared 441 * copy-on-write.) 442 */ 443 if (p1->p_limit->p_lflags & PL_SHAREMOD) 444 p2->p_limit = limcopy(p1->p_limit); 445 else { 446 p2->p_limit = p1->p_limit; 447 p2->p_limit->p_refcnt++; 448 } 449 450 /* 451 * Preserve some more flags in subprocess. P_PROFIL has already 452 * been preserved. 453 */ 454 p2->p_flag |= p1->p_flag & (P_SUGID | P_ALTSTACK); 455 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 456 p2->p_flag |= P_CONTROLT; 457 if (flags & RFPPWAIT) 458 p2->p_flag |= P_PPWAIT; 459 460 LIST_INSERT_AFTER(p1, p2, p_pglist); 461 462 /* 463 * Attach the new process to its parent. 464 * 465 * If RFNOWAIT is set, the newly created process becomes a child 466 * of init. This effectively disassociates the child from the 467 * parent. 468 */ 469 if (flags & RFNOWAIT) 470 pptr = initproc; 471 else 472 pptr = p1; 473 p2->p_pptr = pptr; 474 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling); 475 LIST_INIT(&p2->p_children); 476 varsymset_init(&p2->p_varsymset, &p1->p_varsymset); 477 478 #ifdef KTRACE 479 /* 480 * Copy traceflag and tracefile if enabled. If not inherited, 481 * these were zeroed above but we still could have a trace race 482 * so make sure p2's p_tracep is NULL. 483 */ 484 if ((p1->p_traceflag & KTRFAC_INHERIT) && p2->p_tracep == NULL) { 485 p2->p_traceflag = p1->p_traceflag; 486 if ((p2->p_tracep = p1->p_tracep) != NULL) 487 VREF(p2->p_tracep); 488 } 489 #endif 490 491 /* 492 * set priority of child to be that of parent 493 */ 494 p2->p_estcpu = p1->p_estcpu; 495 496 /* 497 * This begins the section where we must prevent the parent 498 * from being swapped. 499 */ 500 PHOLD(p1); 501 502 /* 503 * Finish creating the child process. It will return via a different 504 * execution path later. (ie: directly into user mode) 505 */ 506 vm_fork(p1, p2, flags); 507 508 if (flags == (RFFDG | RFPROC)) { 509 mycpu->gd_cnt.v_forks++; 510 mycpu->gd_cnt.v_forkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 511 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) { 512 mycpu->gd_cnt.v_vforks++; 513 mycpu->gd_cnt.v_vforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 514 } else if (p1 == &proc0) { 515 mycpu->gd_cnt.v_kthreads++; 516 mycpu->gd_cnt.v_kthreadpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 517 } else { 518 mycpu->gd_cnt.v_rforks++; 519 mycpu->gd_cnt.v_rforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 520 } 521 522 /* 523 * Both processes are set up, now check if any loadable modules want 524 * to adjust anything. 525 * What if they have an error? XXX 526 */ 527 TAILQ_FOREACH(ep, &fork_list, next) { 528 (*ep->function)(p1, p2, flags); 529 } 530 531 /* 532 * Make child runnable and add to run queue. 533 */ 534 microtime(&(p2->p_stats->p_start)); 535 p2->p_acflag = AFORK; 536 537 /* 538 * tell any interested parties about the new process 539 */ 540 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid); 541 542 /* 543 * Return child proc pointer to parent. 544 */ 545 *procp = p2; 546 return (0); 547 } 548 549 /* 550 * The next two functionms are general routines to handle adding/deleting 551 * items on the fork callout list. 552 * 553 * at_fork(): 554 * Take the arguments given and put them onto the fork callout list, 555 * However first make sure that it's not already there. 556 * Returns 0 on success or a standard error number. 557 */ 558 559 int 560 at_fork(function) 561 forklist_fn function; 562 { 563 struct forklist *ep; 564 565 #ifdef INVARIANTS 566 /* let the programmer know if he's been stupid */ 567 if (rm_at_fork(function)) 568 printf("WARNING: fork callout entry (%p) already present\n", 569 function); 570 #endif 571 ep = malloc(sizeof(*ep), M_ATFORK, M_NOWAIT); 572 if (ep == NULL) 573 return (ENOMEM); 574 ep->function = function; 575 TAILQ_INSERT_TAIL(&fork_list, ep, next); 576 return (0); 577 } 578 579 /* 580 * Scan the exit callout list for the given item and remove it.. 581 * Returns the number of items removed (0 or 1) 582 */ 583 584 int 585 rm_at_fork(function) 586 forklist_fn function; 587 { 588 struct forklist *ep; 589 590 TAILQ_FOREACH(ep, &fork_list, next) { 591 if (ep->function == function) { 592 TAILQ_REMOVE(&fork_list, ep, next); 593 free(ep, M_ATFORK); 594 return(1); 595 } 596 } 597 return (0); 598 } 599 600 /* 601 * Add a forked process to the run queue after any remaining setup, such 602 * as setting the fork handler, has been completed. 603 */ 604 605 void 606 start_forked_proc(struct proc *p1, struct proc *p2) 607 { 608 /* 609 * Move from SIDL to RUN queue, and activate the process's thread. 610 * Activation of the thread effectively makes the process "a" 611 * current process, so we do not setrunqueue(). 612 */ 613 KASSERT(p2->p_stat == SIDL, 614 ("cannot start forked process, bad status: %p", p2)); 615 (void) splhigh(); 616 p2->p_stat = SRUN; 617 setrunqueue(p2); 618 (void) spl0(); 619 620 /* 621 * Now can be swapped. 622 */ 623 PRELE(p1); 624 625 /* 626 * Preserve synchronization semantics of vfork. If waiting for 627 * child to exec or exit, set P_PPWAIT on child, and sleep on our 628 * proc (in case of exit). 629 */ 630 while (p2->p_flag & P_PPWAIT) 631 tsleep(p1, 0, "ppwait", 0); 632 } 633 634