xref: /openbsd-src/sys/kern/kern_fork.c (revision 0411e090837b2cc273ac2c5eb2ab4466fb70ad20) 
1 /*	$OpenBSD: kern_fork.c,v 1.164 2014/05/03 22:44:36 guenther Exp $	*/
2 /*	$NetBSD: kern_fork.c,v 1.29 1996/02/09 18:59:34 christos Exp $	*/
3 
4 /*
5  * Copyright (c) 1982, 1986, 1989, 1991, 1993
6  *	The Regents of the University of California.  All rights reserved.
7  * (c) UNIX System Laboratories, Inc.
8  * All or some portions of this file are derived from material licensed
9  * to the University of California by American Telephone and Telegraph
10  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
11  * the permission of UNIX System Laboratories, Inc.
12  *
13  * Redistribution and use in source and binary forms, with or without
14  * modification, are permitted provided that the following conditions
15  * are met:
16  * 1. Redistributions of source code must retain the above copyright
17  *    notice, this list of conditions and the following disclaimer.
18  * 2. Redistributions in binary form must reproduce the above copyright
19  *    notice, this list of conditions and the following disclaimer in the
20  *    documentation and/or other materials provided with the distribution.
21  * 3. Neither the name of the University nor the names of its contributors
22  *    may be used to endorse or promote products derived from this software
23  *    without specific prior written permission.
24  *
25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35  * SUCH DAMAGE.
36  *
37  *	@(#)kern_fork.c	8.6 (Berkeley) 4/8/94
38  */
39 
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/filedesc.h>
43 #include <sys/kernel.h>
44 #include <sys/malloc.h>
45 #include <sys/mount.h>
46 #include <sys/proc.h>
47 #include <sys/exec.h>
48 #include <sys/resourcevar.h>
49 #include <sys/signalvar.h>
50 #include <sys/vnode.h>
51 #include <sys/file.h>
52 #include <sys/acct.h>
53 #include <sys/ktrace.h>
54 #include <sys/sched.h>
55 #include <dev/rndvar.h>
56 #include <sys/pool.h>
57 #include <sys/mman.h>
58 #include <sys/ptrace.h>
59 
60 #include <sys/syscallargs.h>
61 
62 #include "systrace.h"
63 #include <dev/systrace.h>
64 
65 #include <uvm/uvm.h>
66 
67 #ifdef __HAVE_MD_TCB
68 # include <machine/tcb.h>
69 #endif
70 
71 int	nprocesses = 1;		/* process 0 */
72 int	nthreads = 1;		/* proc 0 */
73 int	randompid;		/* when set to 1, pid's go random */
74 struct	forkstat forkstat;
75 
76 void fork_return(void *);
77 void tfork_child_return(void *);
78 int pidtaken(pid_t);
79 
80 void process_new(struct proc *, struct process *, int);
81 
82 void
83 fork_return(void *arg)
84 {
85 	struct proc *p = (struct proc *)arg;
86 
87 	if (p->p_p->ps_flags & PS_TRACED)
88 		psignal(p, SIGTRAP);
89 
90 	child_return(p);
91 }
92 
93 /*ARGSUSED*/
94 int
95 sys_fork(struct proc *p, void *v, register_t *retval)
96 {
97 	int flags;
98 
99 	flags = FORK_FORK;
100 	if (p->p_p->ps_ptmask & PTRACE_FORK)
101 		flags |= FORK_PTRACE;
102 	return (fork1(p, flags, NULL, 0, fork_return, NULL, retval, NULL));
103 }
104 
105 /*ARGSUSED*/
106 int
107 sys_vfork(struct proc *p, void *v, register_t *retval)
108 {
109 	return (fork1(p, FORK_VFORK|FORK_PPWAIT, NULL, 0, NULL,
110 	    NULL, retval, NULL));
111 }
112 
113 int
114 sys___tfork(struct proc *p, void *v, register_t *retval)
115 {
116 	struct sys___tfork_args /* {
117 		syscallarg(const struct __tfork) *param;
118 		syscallarg(size_t) psize;
119 	} */ *uap = v;
120 	size_t psize = SCARG(uap, psize);
121 	struct __tfork param = { 0 };
122 	int flags;
123 	int error;
124 
125 	if (psize == 0 || psize > sizeof(param))
126 		return (EINVAL);
127 	if ((error = copyin(SCARG(uap, param), &param, psize)))
128 		return (error);
129 #ifdef KTRACE
130 	if (KTRPOINT(p, KTR_STRUCT))
131 		ktrstruct(p, "tfork", &param, sizeof(param));
132 #endif
133 
134 	flags = FORK_TFORK | FORK_THREAD | FORK_SIGHAND | FORK_SHAREVM
135 	    | FORK_SHAREFILES;
136 
137 	return (fork1(p, flags, param.tf_stack, param.tf_tid,
138 	    tfork_child_return, param.tf_tcb, retval, NULL));
139 }
140 
141 void
142 tfork_child_return(void *arg)
143 {
144 	struct proc *p = curproc;
145 
146 	TCB_SET(p, arg);
147 	child_return(p);
148 }
149 
150 /*
151  * Allocate and initialize a new process.
152  */
153 void
154 process_new(struct proc *p, struct process *parent, int flags)
155 {
156 	struct process *pr;
157 
158 	pr = pool_get(&process_pool, PR_WAITOK);
159 	pr->ps_mainproc = p;
160 
161 	TAILQ_INIT(&pr->ps_threads);
162 	TAILQ_INSERT_TAIL(&pr->ps_threads, p, p_thr_link);
163 	pr->ps_pptr = parent;
164 	LIST_INIT(&pr->ps_children);
165 	pr->ps_refcnt = 1;
166 
167 	/*
168 	 * Make a process structure for the new process.
169 	 * Start by zeroing the section of proc that is zero-initialized,
170 	 * then copy the section that is copied directly from the parent.
171 	 */
172 	memset(&pr->ps_startzero, 0,
173 	    (caddr_t)&pr->ps_endzero - (caddr_t)&pr->ps_startzero);
174 	memcpy(&pr->ps_startcopy, &parent->ps_startcopy,
175 	    (caddr_t)&pr->ps_endcopy - (caddr_t)&pr->ps_startcopy);
176 
177 	/* post-copy fixups */
178 	pr->ps_ucred = p->p_ucred;
179 	crhold(pr->ps_ucred);
180 	KASSERT(p->p_ucred->cr_ref >= 3); /* fork thr, new thr, new process */
181 	pr->ps_limit->p_refcnt++;
182 
183 	/* bump references to the text vnode (for procfs) */
184 	pr->ps_textvp = parent->ps_textvp;
185 	if (pr->ps_textvp)
186 		vref(pr->ps_textvp);
187 
188 	timeout_set(&pr->ps_realit_to, realitexpire, pr);
189 
190 	pr->ps_flags = parent->ps_flags & (PS_SUGID | PS_SUGIDEXEC);
191 	if (parent->ps_session->s_ttyvp != NULL &&
192 	    parent->ps_flags & PS_CONTROLT)
193 		atomic_setbits_int(&pr->ps_flags, PS_CONTROLT);
194 
195 	p->p_p = pr;
196 
197 	/*
198 	 * Create signal actions for the child process.
199 	 */
200 	if (flags & FORK_SIGHAND)
201 		pr->ps_sigacts = sigactsshare(parent);
202 	else
203 		pr->ps_sigacts = sigactsinit(parent);
204 
205 	if (parent->ps_flags & PS_PROFIL)
206 		startprofclock(pr);
207 	if ((flags & FORK_PTRACE) && (parent->ps_flags & PS_TRACED))
208 		atomic_setbits_int(&pr->ps_flags, PS_TRACED);
209 	if (flags & FORK_NOZOMBIE)
210 		atomic_setbits_int(&pr->ps_flags, PS_NOZOMBIE);
211 
212 	/* it's sufficiently inited to be globally visible */
213 	LIST_INSERT_HEAD(&allprocess, pr, ps_list);
214 }
215 
216 /* print the 'table full' message once per 10 seconds */
217 struct timeval fork_tfmrate = { 10, 0 };
218 
219 int
220 fork1(struct proc *curp, int flags, void *stack, pid_t *tidptr,
221     void (*func)(void *), void *arg, register_t *retval,
222     struct proc **rnewprocp)
223 {
224 	struct process *curpr = curp->p_p;
225 	struct process *pr;
226 	struct proc *p;
227 	uid_t uid;
228 	struct vmspace *vm;
229 	int count;
230 	vaddr_t uaddr;
231 	int s;
232 	struct  ptrace_state *newptstat = NULL;
233 #if NSYSTRACE > 0
234 	void *newstrp = NULL;
235 #endif
236 
237 	/* sanity check some flag combinations */
238 	if (flags & FORK_THREAD) {
239 		if ((flags & FORK_SIGHAND) == 0)
240 			return (EINVAL);
241 	}
242 	if (flags & FORK_SIGHAND && (flags & FORK_SHAREVM) == 0)
243 		return (EINVAL);
244 
245 	/*
246 	 * Although process entries are dynamically created, we still keep
247 	 * a global limit on the maximum number we will create. We reserve
248 	 * the last 5 processes to root. The variable nprocesses is the
249 	 * current number of processes, maxprocess is the limit.  Similar
250 	 * rules for threads (struct proc): we reserve the last 5 to root;
251 	 * the variable nthreads is the current number of procs, maxthread is
252 	 * the limit.
253 	 */
254 	uid = curp->p_ucred->cr_ruid;
255 	if ((nthreads >= maxthread - 5 && uid != 0) || nthreads >= maxthread) {
256 		static struct timeval lasttfm;
257 
258 		if (ratecheck(&lasttfm, &fork_tfmrate))
259 			tablefull("proc");
260 		return (EAGAIN);
261 	}
262 	nthreads++;
263 
264 	if ((flags & FORK_THREAD) == 0) {
265 		if ((nprocesses >= maxprocess - 5 && uid != 0) ||
266 		    nprocesses >= maxprocess) {
267 			static struct timeval lasttfm;
268 
269 			if (ratecheck(&lasttfm, &fork_tfmrate))
270 				tablefull("process");
271 			nthreads--;
272 			return (EAGAIN);
273 		}
274 		nprocesses++;
275 
276 		/*
277 		 * Increment the count of processes running with
278 		 * this uid.  Don't allow a nonprivileged user to
279 		 * exceed their current limit.
280 		 */
281 		count = chgproccnt(uid, 1);
282 		if (uid != 0 && count > curp->p_rlimit[RLIMIT_NPROC].rlim_cur) {
283 			(void)chgproccnt(uid, -1);
284 			nprocesses--;
285 			nthreads--;
286 			return (EAGAIN);
287 		}
288 	}
289 
290 	uaddr = uvm_uarea_alloc();
291 	if (uaddr == 0) {
292 		if ((flags & FORK_THREAD) == 0) {
293 			(void)chgproccnt(uid, -1);
294 			nprocesses--;
295 		}
296 		nthreads--;
297 		return (ENOMEM);
298 	}
299 
300 	/*
301 	 * From now on, we're committed to the fork and cannot fail.
302 	 */
303 
304 	/* Allocate new proc. */
305 	p = pool_get(&proc_pool, PR_WAITOK);
306 
307 	p->p_stat = SIDL;			/* protect against others */
308 	p->p_flag = 0;
309 
310 	/*
311 	 * Make a proc table entry for the new process.
312 	 * Start by zeroing the section of proc that is zero-initialized,
313 	 * then copy the section that is copied directly from the parent.
314 	 */
315 	memset(&p->p_startzero, 0,
316 	    (caddr_t)&p->p_endzero - (caddr_t)&p->p_startzero);
317 	memcpy(&p->p_startcopy, &curp->p_startcopy,
318 	    (caddr_t)&p->p_endcopy - (caddr_t)&p->p_startcopy);
319 	crhold(p->p_ucred);
320 
321 	/*
322 	 * Initialize the timeouts.
323 	 */
324 	timeout_set(&p->p_sleep_to, endtsleep, p);
325 
326 	if (flags & FORK_THREAD) {
327 		atomic_setbits_int(&p->p_flag, P_THREAD);
328 		p->p_p = pr = curpr;
329 		pr->ps_refcnt++;
330 	} else {
331 		process_new(p, curpr, flags);
332 		pr = p->p_p;
333 	}
334 
335 	/*
336 	 * Duplicate sub-structures as needed.
337 	 * Increase reference counts on shared objects.
338 	 */
339 	if (flags & FORK_SHAREFILES)
340 		p->p_fd = fdshare(curp);
341 	else
342 		p->p_fd = fdcopy(curp);
343 
344 	if (flags & FORK_PPWAIT) {
345 		atomic_setbits_int(&pr->ps_flags, PS_PPWAIT);
346 		atomic_setbits_int(&curpr->ps_flags, PS_ISPWAIT);
347 	}
348 
349 #ifdef KTRACE
350 	/*
351 	 * Copy traceflag and tracefile if enabled.
352 	 * If not inherited, these were zeroed above.
353 	 */
354 	if ((flags & FORK_THREAD) == 0 && curpr->ps_traceflag & KTRFAC_INHERIT)
355 		ktrsettrace(pr, curpr->ps_traceflag, curpr->ps_tracevp,
356 		    curpr->ps_tracecred);
357 #endif
358 
359 	/*
360 	 * set priority of child to be that of parent
361 	 * XXX should move p_estcpu into the region of struct proc which gets
362 	 * copied.
363 	 */
364 	scheduler_fork_hook(curp, p);
365 
366 	if (flags & FORK_THREAD)
367 		sigstkinit(&p->p_sigstk);
368 
369 	/*
370 	 * If emulation has thread fork hook, call it now.
371 	 */
372 	if (pr->ps_emul->e_proc_fork)
373 		(*pr->ps_emul->e_proc_fork)(p, curp);
374 
375 	p->p_addr = (struct user *)uaddr;
376 
377 	/*
378 	 * Finish creating the child process.  It will return through a
379 	 * different path later.
380 	 */
381 	uvm_fork(curp, p, ((flags & FORK_SHAREVM) ? TRUE : FALSE), stack,
382 	    0, func ? func : child_return, arg ? arg : p);
383 
384 	vm = p->p_vmspace;
385 
386 	if (flags & FORK_FORK) {
387 		forkstat.cntfork++;
388 		forkstat.sizfork += vm->vm_dsize + vm->vm_ssize;
389 	} else if (flags & FORK_VFORK) {
390 		forkstat.cntvfork++;
391 		forkstat.sizvfork += vm->vm_dsize + vm->vm_ssize;
392 	} else if (flags & FORK_TFORK) {
393 		forkstat.cnttfork++;
394 	} else {
395 		forkstat.cntkthread++;
396 		forkstat.sizkthread += vm->vm_dsize + vm->vm_ssize;
397 	}
398 
399 	if (pr->ps_flags & PS_TRACED && flags & FORK_FORK)
400 		newptstat = malloc(sizeof(*newptstat), M_SUBPROC, M_WAITOK);
401 #if NSYSTRACE > 0
402 	if (ISSET(curp->p_flag, P_SYSTRACE))
403 		newstrp = systrace_getproc();
404 #endif
405 
406 	p->p_pid = allocpid();
407 
408 	LIST_INSERT_HEAD(&allproc, p, p_list);
409 	LIST_INSERT_HEAD(PIDHASH(p->p_pid), p, p_hash);
410 	if ((flags & FORK_THREAD) == 0) {
411 		LIST_INSERT_AFTER(curpr, pr, ps_pglist);
412 		LIST_INSERT_HEAD(&curpr->ps_children, pr, ps_sibling);
413 
414 		if (pr->ps_flags & PS_TRACED) {
415 			pr->ps_oppid = curpr->ps_pid;
416 			if (pr->ps_pptr != curpr->ps_pptr)
417 				proc_reparent(pr, curpr->ps_pptr);
418 
419 			/*
420 			 * Set ptrace status.
421 			 */
422 			if (flags & FORK_FORK) {
423 				pr->ps_ptstat = newptstat;
424 				newptstat = NULL;
425 				curpr->ps_ptstat->pe_report_event = PTRACE_FORK;
426 				pr->ps_ptstat->pe_report_event = PTRACE_FORK;
427 				curpr->ps_ptstat->pe_other_pid = pr->ps_pid;
428 				pr->ps_ptstat->pe_other_pid = curpr->ps_pid;
429 			}
430 		}
431 	} else {
432 		TAILQ_INSERT_TAIL(&pr->ps_threads, p, p_thr_link);
433 		/*
434 		 * if somebody else wants to take us to single threaded mode,
435 		 * count ourselves in.
436 		 */
437 		if (pr->ps_single) {
438 			curpr->ps_singlecount++;
439 			atomic_setbits_int(&p->p_flag, P_SUSPSINGLE);
440 		}
441 	}
442 
443 #if NSYSTRACE > 0
444 	if (newstrp)
445 		systrace_fork(curp, p, newstrp);
446 #endif
447 
448 	if (tidptr != NULL) {
449 		pid_t	pid = p->p_pid + THREAD_PID_OFFSET;
450 
451 		if (copyout(&pid, tidptr, sizeof(pid)))
452 			psignal(curp, SIGSEGV);
453 	}
454 
455 	/*
456 	 * For new processes, set accounting bits
457 	 */
458 	if ((flags & FORK_THREAD) == 0) {
459 		getnanotime(&pr->ps_start);
460 		pr->ps_acflag = AFORK;
461 	}
462 
463 	/*
464 	 * Make child runnable and add to run queue.
465 	 */
466 	if ((flags & FORK_IDLE) == 0) {
467 		SCHED_LOCK(s);
468 		p->p_stat = SRUN;
469 		p->p_cpu = sched_choosecpu_fork(curp, flags);
470 		setrunqueue(p);
471 		SCHED_UNLOCK(s);
472 	} else
473 		p->p_cpu = arg;
474 
475 	if (newptstat)
476 		free(newptstat, M_SUBPROC);
477 
478 	/*
479 	 * Notify any interested parties about the new process.
480 	 */
481 	if ((flags & FORK_THREAD) == 0)
482 		KNOTE(&curpr->ps_klist, NOTE_FORK | p->p_pid);
483 
484 	/*
485 	 * Update stats now that we know the fork was successful.
486 	 */
487 	uvmexp.forks++;
488 	if (flags & FORK_PPWAIT)
489 		uvmexp.forks_ppwait++;
490 	if (flags & FORK_SHAREVM)
491 		uvmexp.forks_sharevm++;
492 
493 	/*
494 	 * Pass a pointer to the new process to the caller.
495 	 */
496 	if (rnewprocp != NULL)
497 		*rnewprocp = p;
498 
499 	/*
500 	 * Preserve synchronization semantics of vfork.  If waiting for
501 	 * child to exec or exit, set PS_PPWAIT on child and PS_ISPWAIT
502 	 * on ourselves, and sleep on our process for the latter flag
503 	 * to go away.
504 	 * XXX Need to stop other rthreads in the parent
505 	 */
506 	if (flags & FORK_PPWAIT)
507 		while (curpr->ps_flags & PS_ISPWAIT)
508 			tsleep(curpr, PWAIT, "ppwait", 0);
509 
510 	/*
511 	 * If we're tracing the child, alert the parent too.
512 	 */
513 	if ((flags & FORK_PTRACE) && (curpr->ps_flags & PS_TRACED))
514 		psignal(curp, SIGTRAP);
515 
516 	/*
517 	 * Return child pid to parent process,
518 	 * marking us as parent via retval[1].
519 	 */
520 	if (retval != NULL) {
521 		retval[0] = p->p_pid +
522 		    (flags & FORK_THREAD ? THREAD_PID_OFFSET : 0);
523 		retval[1] = 0;
524 	}
525 	return (0);
526 }
527 
528 /*
529  * Checks for current use of a pid, either as a pid or pgid.
530  */
531 pid_t oldpids[100];
532 int
533 ispidtaken(pid_t pid)
534 {
535 	uint32_t i;
536 	struct process *pr;
537 
538 	for (i = 0; i < nitems(oldpids); i++)
539 		if (pid == oldpids[i])
540 			return (1);
541 
542 	if (pfind(pid) != NULL)
543 		return (1);
544 	if (pgfind(pid) != NULL)
545 		return (1);
546 	LIST_FOREACH(pr, &zombprocess, ps_list) {
547 		if (pr->ps_pid == pid ||
548 		    (pr->ps_pgrp && pr->ps_pgrp->pg_id == pid))
549 			return (1);
550 	}
551 	return (0);
552 }
553 
554 /* Find an unused pid satisfying 1 <= lastpid <= PID_MAX */
555 pid_t
556 allocpid(void)
557 {
558 	static pid_t lastpid;
559 	pid_t pid;
560 
561 	if (!randompid) {
562 		/* only used early on for system processes */
563 		pid = ++lastpid;
564 	} else {
565 		do {
566 			pid = 1 + arc4random_uniform(PID_MAX);
567 		} while (ispidtaken(pid));
568 	}
569 
570 	return pid;
571 }
572 
573 void
574 freepid(pid_t pid)
575 {
576 	static uint32_t idx;
577 
578 	oldpids[idx++ % nitems(oldpids)] = pid;
579 }
580 
581 #if defined(MULTIPROCESSOR)
582 /*
583  * XXX This is a slight hack to get newly-formed processes to
584  * XXX acquire the kernel lock as soon as they run.
585  */
586 void
587 proc_trampoline_mp(void)
588 {
589 	struct proc *p;
590 
591 	p = curproc;
592 
593 	SCHED_ASSERT_LOCKED();
594 	__mp_unlock(&sched_lock);
595 	spl0();
596 	SCHED_ASSERT_UNLOCKED();
597 	KASSERT(__mp_lock_held(&kernel_lock) == 0);
598 
599 	KERNEL_LOCK();
600 }
601 #endif
602