xref: /openbsd-src/sys/kern/kern_fork.c (revision f065ab1d79aab3a0f39f2a846f60ac4cc6b10d30) 
1 /*	$OpenBSD: kern_fork.c,v 1.123 2010/10/31 00:03:44 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_extern.h>
66 #include <uvm/uvm_map.h>
67 
68 int	nprocs = 1;		/* process 0 */
69 int	randompid;		/* when set to 1, pid's go random */
70 pid_t	lastpid;
71 struct	forkstat forkstat;
72 
73 void fork_return(void *);
74 int pidtaken(pid_t);
75 
76 void process_new(struct proc *, struct proc *);
77 
78 void
79 fork_return(void *arg)
80 {
81 	struct proc *p = (struct proc *)arg;
82 
83 	if (p->p_flag & P_TRACED)
84 		psignal(p, SIGTRAP);
85 
86 	child_return(p);
87 }
88 
89 /*ARGSUSED*/
90 int
91 sys_fork(struct proc *p, void *v, register_t *retval)
92 {
93 	int flags;
94 
95 	flags = FORK_FORK;
96 	if (p->p_ptmask & PTRACE_FORK)
97 		flags |= FORK_PTRACE;
98 	return (fork1(p, SIGCHLD, flags, NULL, 0,
99 	    fork_return, NULL, retval, NULL));
100 }
101 
102 /*ARGSUSED*/
103 int
104 sys_vfork(struct proc *p, void *v, register_t *retval)
105 {
106 	return (fork1(p, SIGCHLD, FORK_VFORK|FORK_PPWAIT, NULL, 0, NULL,
107 	    NULL, retval, NULL));
108 }
109 
110 int
111 sys_rfork(struct proc *p, void *v, register_t *retval)
112 {
113 	struct sys_rfork_args /* {
114 		syscallarg(int) flags;
115 	} */ *uap = v;
116 
117 	int rforkflags;
118 	int flags;
119 
120 	flags = FORK_RFORK;
121 	rforkflags = SCARG(uap, flags);
122 
123 	if ((rforkflags & RFPROC) == 0)
124 		return (EINVAL);
125 
126 	switch(rforkflags & (RFFDG|RFCFDG)) {
127 	case (RFFDG|RFCFDG):
128 		return EINVAL;
129 	case RFCFDG:
130 		flags |= FORK_CLEANFILES;
131 		break;
132 	case RFFDG:
133 		break;
134 	default:
135 		flags |= FORK_SHAREFILES;
136 		break;
137 	}
138 
139 	if (rforkflags & RFNOWAIT)
140 		flags |= FORK_NOZOMBIE;
141 
142 	if (rforkflags & RFMEM)
143 		flags |= FORK_SHAREVM;
144 
145 	if (rforkflags & RFTHREAD)
146 		flags |= FORK_THREAD | FORK_SIGHAND | FORK_NOZOMBIE;
147 
148 	return (fork1(p, SIGCHLD, flags, NULL, 0, NULL, NULL, retval, NULL));
149 }
150 
151 /*
152  * Allocate and initialize a new process.
153  */
154 void
155 process_new(struct proc *newproc, struct proc *parentproc)
156 {
157 	struct process *pr, *parent;
158 
159 	pr = pool_get(&process_pool, PR_WAITOK);
160 	pr->ps_mainproc = newproc;
161 	parent = parentproc->p_p;
162 
163 	TAILQ_INIT(&pr->ps_threads);
164 	TAILQ_INSERT_TAIL(&pr->ps_threads, newproc, p_thr_link);
165 	LIST_INSERT_AFTER(parent, pr, ps_pglist);
166 	pr->ps_pptr = parent;
167 	LIST_INSERT_HEAD(&parent->ps_children, pr, ps_sibling);
168 	LIST_INIT(&pr->ps_children);
169 	pr->ps_refcnt = 1;
170 
171 	/*
172 	 * Make a process structure for the new process.
173 	 * Start by zeroing the section of proc that is zero-initialized,
174 	 * then copy the section that is copied directly from the parent.
175 	 */
176 	bzero(&pr->ps_startzero,
177 	    (unsigned) ((caddr_t)&pr->ps_endzero - (caddr_t)&pr->ps_startzero));
178 	bcopy(&parent->ps_startcopy, &pr->ps_startcopy,
179 	    (unsigned) ((caddr_t)&pr->ps_endcopy - (caddr_t)&pr->ps_startcopy));
180 
181 	/* post-copy fixups */
182 	pr->ps_cred = pool_get(&pcred_pool, PR_WAITOK);
183 	bcopy(parent->ps_cred, pr->ps_cred, sizeof(*pr->ps_cred));
184 	crhold(parent->ps_cred->pc_ucred);
185 	pr->ps_limit->p_refcnt++;
186 
187 	if (parent->ps_session->s_ttyvp != NULL &&
188 	    parent->ps_flags & PS_CONTROLT)
189 		atomic_setbits_int(&pr->ps_flags, PS_CONTROLT);
190 
191 	newproc->p_p = pr;
192 }
193 
194 /* print the 'table full' message once per 10 seconds */
195 struct timeval fork_tfmrate = { 10, 0 };
196 
197 int
198 fork1(struct proc *p1, int exitsig, int flags, void *stack, size_t stacksize,
199     void (*func)(void *), void *arg, register_t *retval,
200     struct proc **rnewprocp)
201 {
202 	struct proc *p2;
203 	uid_t uid;
204 	struct vmspace *vm;
205 	int count;
206 	vaddr_t uaddr;
207 	int s;
208 	extern void endtsleep(void *);
209 	extern void realitexpire(void *);
210 	struct  ptrace_state *newptstat = NULL;
211 #if NSYSTRACE > 0
212 	void *newstrp = NULL;
213 #endif
214 
215 	/* sanity check some flag combinations */
216 	if (flags & FORK_THREAD) {
217 		if (!rthreads_enabled)
218 			return (ENOTSUP);
219 		if ((flags & (FORK_SIGHAND | FORK_NOZOMBIE)) !=
220 		    (FORK_SIGHAND | FORK_NOZOMBIE))
221 			return (EINVAL);
222 	}
223 	if (flags & FORK_SIGHAND && (flags & FORK_SHAREVM) == 0)
224 		return (EINVAL);
225 
226 	/*
227 	 * Although process entries are dynamically created, we still keep
228 	 * a global limit on the maximum number we will create. We reserve
229 	 * the last 5 processes to root. The variable nprocs is the current
230 	 * number of processes, maxproc is the limit.
231 	 */
232 	uid = p1->p_cred->p_ruid;
233 	if ((nprocs >= maxproc - 5 && uid != 0) || nprocs >= maxproc) {
234 		static struct timeval lasttfm;
235 
236 		if (ratecheck(&lasttfm, &fork_tfmrate))
237 			tablefull("proc");
238 		return (EAGAIN);
239 	}
240 	nprocs++;
241 
242 	/*
243 	 * Increment the count of procs running with this uid. Don't allow
244 	 * a nonprivileged user to exceed their current limit.
245 	 */
246 	count = chgproccnt(uid, 1);
247 	if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) {
248 		(void)chgproccnt(uid, -1);
249 		nprocs--;
250 		return (EAGAIN);
251 	}
252 
253 	uaddr = uvm_km_kmemalloc_pla(kernel_map, uvm.kernel_object, USPACE,
254 	    USPACE_ALIGN, UVM_KMF_ZERO,
255 	    dma_constraint.ucr_low, dma_constraint.ucr_high,
256 	    0, 0, USPACE/PAGE_SIZE);
257 	if (uaddr == 0) {
258 		chgproccnt(uid, -1);
259 		nprocs--;
260 		return (ENOMEM);
261 	}
262 
263 	/*
264 	 * From now on, we're committed to the fork and cannot fail.
265 	 */
266 
267 	/* Allocate new proc. */
268 	p2 = pool_get(&proc_pool, PR_WAITOK);
269 
270 	p2->p_stat = SIDL;			/* protect against others */
271 	p2->p_exitsig = exitsig;
272 	p2->p_flag = 0;
273 
274 	if (flags & FORK_THREAD) {
275 		atomic_setbits_int(&p2->p_flag, P_THREAD);
276 		p2->p_p = p1->p_p;
277 		TAILQ_INSERT_TAIL(&p2->p_p->ps_threads, p2, p_thr_link);
278 		p2->p_p->ps_refcnt++;
279 	} else {
280 		process_new(p2, p1);
281 	}
282 
283 	/*
284 	 * Make a proc table entry for the new process.
285 	 * Start by zeroing the section of proc that is zero-initialized,
286 	 * then copy the section that is copied directly from the parent.
287 	 */
288 	bzero(&p2->p_startzero,
289 	    (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
290 	bcopy(&p1->p_startcopy, &p2->p_startcopy,
291 	    (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
292 
293 	/*
294 	 * Initialize the timeouts.
295 	 */
296 	timeout_set(&p2->p_sleep_to, endtsleep, p2);
297 	timeout_set(&p2->p_realit_to, realitexpire, p2);
298 
299 	/*
300 	 * Duplicate sub-structures as needed.
301 	 * Increase reference counts on shared objects.
302 	 * The p_stats and p_sigacts substructs are set in vm_fork.
303 	 */
304 	if (p1->p_flag & P_PROFIL)
305 		startprofclock(p2);
306 	atomic_setbits_int(&p2->p_flag, p1->p_flag & (P_SUGID | P_SUGIDEXEC));
307 	if (flags & FORK_PTRACE)
308 		atomic_setbits_int(&p2->p_flag, p1->p_flag & P_TRACED);
309 
310 	/* bump references to the text vnode (for procfs) */
311 	p2->p_textvp = p1->p_textvp;
312 	if (p2->p_textvp)
313 		vref(p2->p_textvp);
314 
315 	if (flags & FORK_CLEANFILES)
316 		p2->p_fd = fdinit(p1);
317 	else if (flags & FORK_SHAREFILES)
318 		p2->p_fd = fdshare(p1);
319 	else
320 		p2->p_fd = fdcopy(p1);
321 
322 	if (flags & FORK_PPWAIT)
323 		atomic_setbits_int(&p2->p_flag, P_PPWAIT);
324 	if (flags & FORK_NOZOMBIE)
325 		atomic_setbits_int(&p2->p_flag, P_NOZOMBIE);
326 
327 #ifdef KTRACE
328 	/*
329 	 * Copy traceflag and tracefile if enabled.
330 	 * If not inherited, these were zeroed above.
331 	 */
332 	if (p1->p_traceflag & KTRFAC_INHERIT) {
333 		p2->p_traceflag = p1->p_traceflag;
334 		if ((p2->p_tracep = p1->p_tracep) != NULL)
335 			vref(p2->p_tracep);
336 	}
337 #endif
338 
339 	/*
340 	 * set priority of child to be that of parent
341 	 * XXX should move p_estcpu into the region of struct proc which gets
342 	 * copied.
343 	 */
344 	scheduler_fork_hook(p1, p2);
345 
346 	/*
347 	 * Create signal actions for the child process.
348 	 */
349 	if (flags & FORK_SIGHAND)
350 		sigactsshare(p1, p2);
351 	else
352 		p2->p_sigacts = sigactsinit(p1);
353 
354 	/*
355 	 * If emulation has process fork hook, call it now.
356 	 */
357 	if (p2->p_emul->e_proc_fork)
358 		(*p2->p_emul->e_proc_fork)(p2, p1);
359 
360 	p2->p_addr = (struct user *)uaddr;
361 
362 	/*
363 	 * Finish creating the child process.  It will return through a
364 	 * different path later.
365 	 */
366 	uvm_fork(p1, p2, ((flags & FORK_SHAREVM) ? TRUE : FALSE), stack,
367 	    stacksize, func ? func : child_return, arg ? arg : p2);
368 
369 	timeout_set(&p2->p_stats->p_virt_to, virttimer_trampoline, p2);
370 	timeout_set(&p2->p_stats->p_prof_to, proftimer_trampoline, p2);
371 
372 	vm = p2->p_vmspace;
373 
374 	if (flags & FORK_FORK) {
375 		forkstat.cntfork++;
376 		forkstat.sizfork += vm->vm_dsize + vm->vm_ssize;
377 	} else if (flags & FORK_VFORK) {
378 		forkstat.cntvfork++;
379 		forkstat.sizvfork += vm->vm_dsize + vm->vm_ssize;
380 	} else if (flags & FORK_RFORK) {
381 		forkstat.cntrfork++;
382 		forkstat.sizrfork += vm->vm_dsize + vm->vm_ssize;
383 	} else {
384 		forkstat.cntkthread++;
385 		forkstat.sizkthread += vm->vm_dsize + vm->vm_ssize;
386 	}
387 
388 	if (p2->p_flag & P_TRACED && flags & FORK_FORK)
389 		newptstat = malloc(sizeof(*newptstat), M_SUBPROC, M_WAITOK);
390 #if NSYSTRACE > 0
391 	if (ISSET(p1->p_flag, P_SYSTRACE))
392 		newstrp = systrace_getproc();
393 #endif
394 
395 	/* Find an unused pid satisfying 1 <= lastpid <= PID_MAX */
396 	do {
397 		lastpid = 1 + (randompid ? arc4random() : lastpid) % PID_MAX;
398 	} while (pidtaken(lastpid));
399 	p2->p_pid = lastpid;
400 
401 	LIST_INSERT_HEAD(&allproc, p2, p_list);
402 	LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
403 
404 	if (p2->p_flag & P_TRACED) {
405 		p2->p_oppid = p1->p_pid;
406 		if ((flags & FORK_THREAD) == 0 &&
407 		    p2->p_p->ps_pptr != p1->p_p->ps_pptr)
408 			proc_reparent(p2->p_p, p1->p_p->ps_pptr);
409 
410 		/*
411 		 * Set ptrace status.
412 		 */
413 		if (flags & FORK_FORK) {
414 			p2->p_ptstat = newptstat;
415 			newptstat = NULL;
416 			p1->p_ptstat->pe_report_event = PTRACE_FORK;
417 			p2->p_ptstat->pe_report_event = PTRACE_FORK;
418 			p1->p_ptstat->pe_other_pid = p2->p_pid;
419 			p2->p_ptstat->pe_other_pid = p1->p_pid;
420 		}
421 	}
422 
423 #if NSYSTRACE > 0
424 	if (newstrp)
425 		systrace_fork(p1, p2, newstrp);
426 #endif
427 
428 	/*
429 	 * Make child runnable, set start time, and add to run queue.
430 	 */
431 	SCHED_LOCK(s);
432  	getmicrotime(&p2->p_stats->p_start);
433 	p2->p_acflag = AFORK;
434 	p2->p_stat = SRUN;
435 	p2->p_cpu = sched_choosecpu_fork(p1, flags);
436 	setrunqueue(p2);
437 	SCHED_UNLOCK(s);
438 
439 	if (newptstat)
440 		free(newptstat, M_SUBPROC);
441 
442 	/*
443 	 * Notify any interested parties about the new process.
444 	 */
445 	if ((flags & FORK_THREAD) == 0)
446 		KNOTE(&p1->p_p->ps_klist, NOTE_FORK | p2->p_pid);
447 
448 	/*
449 	 * Update stats now that we know the fork was successful.
450 	 */
451 	uvmexp.forks++;
452 	if (flags & FORK_PPWAIT)
453 		uvmexp.forks_ppwait++;
454 	if (flags & FORK_SHAREVM)
455 		uvmexp.forks_sharevm++;
456 
457 	/*
458 	 * Pass a pointer to the new process to the caller.
459 	 */
460 	if (rnewprocp != NULL)
461 		*rnewprocp = p2;
462 
463 	/*
464 	 * Preserve synchronization semantics of vfork.  If waiting for
465 	 * child to exec or exit, set P_PPWAIT on child, and sleep on our
466 	 * process (in case of exit).
467 	 */
468 	if (flags & FORK_PPWAIT)
469 		while (p2->p_flag & P_PPWAIT)
470 			tsleep(p1->p_p, PWAIT, "ppwait", 0);
471 
472 	/*
473 	 * If we're tracing the child, alert the parent too.
474 	 */
475 	if ((flags & FORK_PTRACE) && (p1->p_flag & P_TRACED))
476 		psignal(p1, SIGTRAP);
477 
478 	/*
479 	 * Return child pid to parent process,
480 	 * marking us as parent via retval[1].
481 	 */
482 	if (retval != NULL) {
483 		retval[0] = p2->p_pid +
484 		    (flags & FORK_THREAD ? THREAD_PID_OFFSET : 0);
485 		retval[1] = 0;
486 	}
487 	return (0);
488 }
489 
490 /*
491  * Checks for current use of a pid, either as a pid or pgid.
492  */
493 int
494 pidtaken(pid_t pid)
495 {
496 	struct proc *p;
497 
498 	if (pfind(pid) != NULL)
499 		return (1);
500 	if (pgfind(pid) != NULL)
501 		return (1);
502 	LIST_FOREACH(p, &zombproc, p_list) {
503 		if (p->p_pid == pid || (p->p_p->ps_pgrp && p->p_p->ps_pgrp->pg_id == pid))
504 			return (1);
505 	}
506 	return (0);
507 }
508 
509 #if defined(MULTIPROCESSOR)
510 /*
511  * XXX This is a slight hack to get newly-formed processes to
512  * XXX acquire the kernel lock as soon as they run.
513  */
514 void
515 proc_trampoline_mp(void)
516 {
517 	struct proc *p;
518 
519 	p = curproc;
520 
521 	SCHED_ASSERT_LOCKED();
522 	__mp_unlock(&sched_lock);
523 	spl0();
524 	SCHED_ASSERT_UNLOCKED();
525 	KASSERT(__mp_lock_held(&kernel_lock) == 0);
526 
527 	KERNEL_PROC_LOCK(p);
528 }
529 #endif
530