kern_fork.c revision 1.191 1 /* $NetBSD: kern_fork.c,v 1.191 2012/07/27 20:52:49 christos Exp $ */
2
3 /*-
4 * Copyright (c) 1999, 2001, 2004, 2006, 2007, 2008 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
9 * NASA Ames Research Center, by Charles M. Hannum, and by Andrew Doran.
10 *
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
13 * are met:
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in the
18 * documentation and/or other materials provided with the distribution.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
22 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
23 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
24 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
25 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
26 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
27 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
28 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
29 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
30 * POSSIBILITY OF SUCH DAMAGE.
31 */
32
33 /*
34 * Copyright (c) 1982, 1986, 1989, 1991, 1993
35 * The Regents of the University of California. All rights reserved.
36 * (c) UNIX System Laboratories, Inc.
37 * All or some portions of this file are derived from material licensed
38 * to the University of California by American Telephone and Telegraph
39 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
40 * the permission of UNIX System Laboratories, Inc.
41 *
42 * Redistribution and use in source and binary forms, with or without
43 * modification, are permitted provided that the following conditions
44 * are met:
45 * 1. Redistributions of source code must retain the above copyright
46 * notice, this list of conditions and the following disclaimer.
47 * 2. Redistributions in binary form must reproduce the above copyright
48 * notice, this list of conditions and the following disclaimer in the
49 * documentation and/or other materials provided with the distribution.
50 * 3. Neither the name of the University nor the names of its contributors
51 * may be used to endorse or promote products derived from this software
52 * without specific prior written permission.
53 *
54 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
55 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
56 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
57 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
58 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
59 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
60 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
61 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
62 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
63 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
64 * SUCH DAMAGE.
65 *
66 * @(#)kern_fork.c 8.8 (Berkeley) 2/14/95
67 */
68
69 #include <sys/cdefs.h>
70 __KERNEL_RCSID(0, "$NetBSD: kern_fork.c,v 1.191 2012/07/27 20:52:49 christos Exp $");
71
72 #include "opt_ktrace.h"
73
74 #include <sys/param.h>
75 #include <sys/systm.h>
76 #include <sys/filedesc.h>
77 #include <sys/kernel.h>
78 #include <sys/pool.h>
79 #include <sys/mount.h>
80 #include <sys/proc.h>
81 #include <sys/ras.h>
82 #include <sys/resourcevar.h>
83 #include <sys/vnode.h>
84 #include <sys/file.h>
85 #include <sys/acct.h>
86 #include <sys/ktrace.h>
87 #include <sys/sched.h>
88 #include <sys/signalvar.h>
89 #include <sys/kauth.h>
90 #include <sys/atomic.h>
91 #include <sys/syscallargs.h>
92 #include <sys/uidinfo.h>
93 #include <sys/sdt.h>
94 #include <sys/ptrace.h>
95
96 #include <uvm/uvm_extern.h>
97
98 /*
99 * DTrace SDT provider definitions
100 */
101 SDT_PROBE_DEFINE(proc,,,create,
102 "struct proc *", NULL, /* new process */
103 "struct proc *", NULL, /* parent process */
104 "int", NULL, /* flags */
105 NULL, NULL, NULL, NULL);
106
107 u_int nprocs __cacheline_aligned = 1; /* process 0 */
108
109 /*
110 * Number of ticks to sleep if fork() would fail due to process hitting
111 * limits. Exported in miliseconds to userland via sysctl.
112 */
113 int forkfsleep = 0;
114
115 int
116 sys_fork(struct lwp *l, const void *v, register_t *retval)
117 {
118
119 return fork1(l, 0, SIGCHLD, NULL, 0, NULL, NULL, retval, NULL);
120 }
121
122 /*
123 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM).
124 * Address space is not shared, but parent is blocked until child exit.
125 */
126 int
127 sys_vfork(struct lwp *l, const void *v, register_t *retval)
128 {
129
130 return fork1(l, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL,
131 retval, NULL);
132 }
133
134 /*
135 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2)
136 * semantics. Address space is shared, and parent is blocked until child exit.
137 */
138 int
139 sys___vfork14(struct lwp *l, const void *v, register_t *retval)
140 {
141
142 return fork1(l, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0,
143 NULL, NULL, retval, NULL);
144 }
145
146 /*
147 * Linux-compatible __clone(2) system call.
148 */
149 int
150 sys___clone(struct lwp *l, const struct sys___clone_args *uap,
151 register_t *retval)
152 {
153 /* {
154 syscallarg(int) flags;
155 syscallarg(void *) stack;
156 } */
157 int flags, sig;
158
159 /*
160 * We don't support the CLONE_PID or CLONE_PTRACE flags.
161 */
162 if (SCARG(uap, flags) & (CLONE_PID|CLONE_PTRACE))
163 return EINVAL;
164
165 /*
166 * Linux enforces CLONE_VM with CLONE_SIGHAND, do same.
167 */
168 if (SCARG(uap, flags) & CLONE_SIGHAND
169 && (SCARG(uap, flags) & CLONE_VM) == 0)
170 return EINVAL;
171
172 flags = 0;
173
174 if (SCARG(uap, flags) & CLONE_VM)
175 flags |= FORK_SHAREVM;
176 if (SCARG(uap, flags) & CLONE_FS)
177 flags |= FORK_SHARECWD;
178 if (SCARG(uap, flags) & CLONE_FILES)
179 flags |= FORK_SHAREFILES;
180 if (SCARG(uap, flags) & CLONE_SIGHAND)
181 flags |= FORK_SHARESIGS;
182 if (SCARG(uap, flags) & CLONE_VFORK)
183 flags |= FORK_PPWAIT;
184
185 sig = SCARG(uap, flags) & CLONE_CSIGNAL;
186 if (sig < 0 || sig >= _NSIG)
187 return EINVAL;
188
189 /*
190 * Note that the Linux API does not provide a portable way of
191 * specifying the stack area; the caller must know if the stack
192 * grows up or down. So, we pass a stack size of 0, so that the
193 * code that makes this adjustment is a noop.
194 */
195 return fork1(l, flags, sig, SCARG(uap, stack), 0,
196 NULL, NULL, retval, NULL);
197 }
198
199 /*
200 * Print the 'table full' message once per 10 seconds.
201 */
202 static struct timeval fork_tfmrate = { 10, 0 };
203
204 /*
205 * General fork call. Note that another LWP in the process may call exec()
206 * or exit() while we are forking. It's safe to continue here, because
207 * neither operation will complete until all LWPs have exited the process.
208 */
209 int
210 fork1(struct lwp *l1, int flags, int exitsig, void *stack, size_t stacksize,
211 void (*func)(void *), void *arg, register_t *retval,
212 struct proc **rnewprocp)
213 {
214 struct proc *p1, *p2, *parent;
215 struct plimit *p1_lim;
216 uid_t uid;
217 struct lwp *l2;
218 int count;
219 vaddr_t uaddr;
220 int tnprocs;
221 int tracefork;
222 int error = 0;
223
224 p1 = l1->l_proc;
225 uid = kauth_cred_getuid(l1->l_cred);
226 tnprocs = atomic_inc_uint_nv(&nprocs);
227
228 /*
229 * Although process entries are dynamically created, we still keep
230 * a global limit on the maximum number we will create.
231 */
232 if (__predict_false(tnprocs >= maxproc))
233 error = -1;
234 else
235 error = kauth_authorize_process(l1->l_cred,
236 KAUTH_PROCESS_FORK, p1, KAUTH_ARG(tnprocs), NULL, NULL);
237
238 if (error) {
239 static struct timeval lasttfm;
240 atomic_dec_uint(&nprocs);
241 if (ratecheck(&lasttfm, &fork_tfmrate))
242 tablefull("proc", "increase kern.maxproc or NPROC");
243 if (forkfsleep)
244 kpause("forkmx", false, forkfsleep, NULL);
245 return EAGAIN;
246 }
247
248 /*
249 * Enforce limits.
250 */
251 count = chgproccnt(uid, 1);
252 if (__predict_false(count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) {
253 if (kauth_authorize_process(l1->l_cred, KAUTH_PROCESS_RLIMIT,
254 p1, KAUTH_ARG(KAUTH_REQ_PROCESS_RLIMIT_BYPASS),
255 &p1->p_rlimit[RLIMIT_NPROC], KAUTH_ARG(RLIMIT_NPROC)) != 0) {
256 (void)chgproccnt(uid, -1);
257 atomic_dec_uint(&nprocs);
258 if (forkfsleep)
259 kpause("forkulim", false, forkfsleep, NULL);
260 return EAGAIN;
261 }
262 }
263
264 /*
265 * Allocate virtual address space for the U-area now, while it
266 * is still easy to abort the fork operation if we're out of
267 * kernel virtual address space.
268 */
269 uaddr = uvm_uarea_alloc();
270 if (__predict_false(uaddr == 0)) {
271 (void)chgproccnt(uid, -1);
272 atomic_dec_uint(&nprocs);
273 return ENOMEM;
274 }
275
276 /*
277 * We are now committed to the fork. From here on, we may
278 * block on resources, but resource allocation may NOT fail.
279 */
280
281 /* Allocate new proc. */
282 p2 = proc_alloc();
283
284 /*
285 * Make a proc table entry for the new process.
286 * Start by zeroing the section of proc that is zero-initialized,
287 * then copy the section that is copied directly from the parent.
288 */
289 memset(&p2->p_startzero, 0,
290 (unsigned) ((char *)&p2->p_endzero - (char *)&p2->p_startzero));
291 memcpy(&p2->p_startcopy, &p1->p_startcopy,
292 (unsigned) ((char *)&p2->p_endcopy - (char *)&p2->p_startcopy));
293
294 CIRCLEQ_INIT(&p2->p_sigpend.sp_info);
295
296 LIST_INIT(&p2->p_lwps);
297 LIST_INIT(&p2->p_sigwaiters);
298
299 /*
300 * Duplicate sub-structures as needed.
301 * Increase reference counts on shared objects.
302 * Inherit flags we want to keep. The flags related to SIGCHLD
303 * handling are important in order to keep a consistent behaviour
304 * for the child after the fork. If we are a 32-bit process, the
305 * child will be too.
306 */
307 p2->p_flag =
308 p1->p_flag & (PK_SUGID | PK_NOCLDWAIT | PK_CLDSIGIGN | PK_32);
309 p2->p_emul = p1->p_emul;
310 p2->p_execsw = p1->p_execsw;
311
312 if (flags & FORK_SYSTEM) {
313 /*
314 * Mark it as a system process. Set P_NOCLDWAIT so that
315 * children are reparented to init(8) when they exit.
316 * init(8) can easily wait them out for us.
317 */
318 p2->p_flag |= (PK_SYSTEM | PK_NOCLDWAIT);
319 }
320
321 mutex_init(&p2->p_stmutex, MUTEX_DEFAULT, IPL_HIGH);
322 mutex_init(&p2->p_auxlock, MUTEX_DEFAULT, IPL_NONE);
323 rw_init(&p2->p_reflock);
324 cv_init(&p2->p_waitcv, "wait");
325 cv_init(&p2->p_lwpcv, "lwpwait");
326
327 /*
328 * Share a lock between the processes if they are to share signal
329 * state: we must synchronize access to it.
330 */
331 if (flags & FORK_SHARESIGS) {
332 p2->p_lock = p1->p_lock;
333 mutex_obj_hold(p1->p_lock);
334 } else
335 p2->p_lock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_NONE);
336
337 kauth_proc_fork(p1, p2);
338
339 p2->p_raslist = NULL;
340 #if defined(__HAVE_RAS)
341 ras_fork(p1, p2);
342 #endif
343
344 /* bump references to the text vnode (for procfs) */
345 p2->p_textvp = p1->p_textvp;
346 if (p2->p_textvp)
347 vref(p2->p_textvp);
348
349 if (flags & FORK_SHAREFILES)
350 fd_share(p2);
351 else if (flags & FORK_CLEANFILES)
352 p2->p_fd = fd_init(NULL);
353 else
354 p2->p_fd = fd_copy();
355
356 /* XXX racy */
357 p2->p_mqueue_cnt = p1->p_mqueue_cnt;
358
359 if (flags & FORK_SHARECWD)
360 cwdshare(p2);
361 else
362 p2->p_cwdi = cwdinit();
363
364 /*
365 * Note: p_limit (rlimit stuff) is copy-on-write, so normally
366 * we just need increase pl_refcnt.
367 */
368 p1_lim = p1->p_limit;
369 if (!p1_lim->pl_writeable) {
370 lim_addref(p1_lim);
371 p2->p_limit = p1_lim;
372 } else {
373 p2->p_limit = lim_copy(p1_lim);
374 }
375
376 if (flags & FORK_PPWAIT) {
377 /* Mark ourselves as waiting for a child. */
378 l1->l_pflag |= LP_VFORKWAIT;
379 p2->p_lflag = PL_PPWAIT;
380 p2->p_vforklwp = l1;
381 } else {
382 p2->p_lflag = 0;
383 }
384 p2->p_sflag = 0;
385 p2->p_slflag = 0;
386 parent = (flags & FORK_NOWAIT) ? initproc : p1;
387 p2->p_pptr = parent;
388 p2->p_ppid = parent->p_pid;
389 LIST_INIT(&p2->p_children);
390
391 p2->p_aio = NULL;
392
393 #ifdef KTRACE
394 /*
395 * Copy traceflag and tracefile if enabled.
396 * If not inherited, these were zeroed above.
397 */
398 if (p1->p_traceflag & KTRFAC_INHERIT) {
399 mutex_enter(&ktrace_lock);
400 p2->p_traceflag = p1->p_traceflag;
401 if ((p2->p_tracep = p1->p_tracep) != NULL)
402 ktradref(p2);
403 mutex_exit(&ktrace_lock);
404 }
405 #endif
406
407 /*
408 * Create signal actions for the child process.
409 */
410 p2->p_sigacts = sigactsinit(p1, flags & FORK_SHARESIGS);
411 mutex_enter(p1->p_lock);
412 p2->p_sflag |=
413 (p1->p_sflag & (PS_STOPFORK | PS_STOPEXEC | PS_NOCLDSTOP));
414 sched_proc_fork(p1, p2);
415 mutex_exit(p1->p_lock);
416
417 p2->p_stflag = p1->p_stflag;
418
419 /*
420 * p_stats.
421 * Copy parts of p_stats, and zero out the rest.
422 */
423 p2->p_stats = pstatscopy(p1->p_stats);
424
425 /*
426 * Set up the new process address space.
427 */
428 uvm_proc_fork(p1, p2, (flags & FORK_SHAREVM) ? true : false);
429
430 /*
431 * Finish creating the child process.
432 * It will return through a different path later.
433 */
434 lwp_create(l1, p2, uaddr, (flags & FORK_PPWAIT) ? LWP_VFORK : 0,
435 stack, stacksize, (func != NULL) ? func : child_return, arg, &l2,
436 l1->l_class);
437
438 /*
439 * Inherit l_private from the parent.
440 * Note that we cannot use lwp_setprivate() here since that
441 * also sets the CPU TLS register, which is incorrect if the
442 * process has changed that without letting the kernel know.
443 */
444 l2->l_private = l1->l_private;
445
446 /*
447 * If emulation has a process fork hook, call it now.
448 */
449 if (p2->p_emul->e_proc_fork)
450 (*p2->p_emul->e_proc_fork)(p2, l1, flags);
451
452 /*
453 * ...and finally, any other random fork hooks that subsystems
454 * might have registered.
455 */
456 doforkhooks(p2, p1);
457
458 SDT_PROBE(proc,,,create, p2, p1, flags, 0, 0);
459
460 /*
461 * It's now safe for the scheduler and other processes to see the
462 * child process.
463 */
464 mutex_enter(proc_lock);
465
466 if (p1->p_session->s_ttyvp != NULL && p1->p_lflag & PL_CONTROLT)
467 p2->p_lflag |= PL_CONTROLT;
468
469 LIST_INSERT_HEAD(&parent->p_children, p2, p_sibling);
470 p2->p_exitsig = exitsig; /* signal for parent on exit */
471
472 /*
473 * We don't want to tracefork vfork()ed processes because they
474 * will not receive the SIGTRAP until it is too late.
475 */
476 tracefork = (p1->p_slflag & (PSL_TRACEFORK|PSL_TRACED)) ==
477 (PSL_TRACEFORK|PSL_TRACED) && (flags && FORK_PPWAIT) == 0;
478 if (tracefork) {
479 p2->p_slflag |= PSL_TRACED;
480 p2->p_opptr = p2->p_pptr;
481 if (p2->p_pptr != p1->p_pptr) {
482 struct proc *parent1 = p2->p_pptr;
483
484 if (parent1->p_lock < p2->p_lock) {
485 if (!mutex_tryenter(parent1->p_lock)) {
486 mutex_exit(p2->p_lock);
487 mutex_enter(parent1->p_lock);
488 }
489 } else if (parent1->p_lock > p2->p_lock) {
490 mutex_enter(parent1->p_lock);
491 }
492 parent1->p_slflag |= PSL_CHTRACED;
493 proc_reparent(p2, p1->p_pptr);
494 if (parent1->p_lock != p2->p_lock)
495 mutex_exit(parent1->p_lock);
496 }
497
498 /*
499 * Set ptrace status.
500 */
501 p1->p_fpid = p2->p_pid;
502 p2->p_fpid = p1->p_pid;
503 }
504
505 LIST_INSERT_AFTER(p1, p2, p_pglist);
506 LIST_INSERT_HEAD(&allproc, p2, p_list);
507
508 p2->p_trace_enabled = trace_is_enabled(p2);
509 #ifdef __HAVE_SYSCALL_INTERN
510 (*p2->p_emul->e_syscall_intern)(p2);
511 #endif
512
513 /*
514 * Update stats now that we know the fork was successful.
515 */
516 uvmexp.forks++;
517 if (flags & FORK_PPWAIT)
518 uvmexp.forks_ppwait++;
519 if (flags & FORK_SHAREVM)
520 uvmexp.forks_sharevm++;
521
522 /*
523 * Pass a pointer to the new process to the caller.
524 */
525 if (rnewprocp != NULL)
526 *rnewprocp = p2;
527
528 if (ktrpoint(KTR_EMUL))
529 p2->p_traceflag |= KTRFAC_TRC_EMUL;
530
531 /*
532 * Notify any interested parties about the new process.
533 */
534 if (!SLIST_EMPTY(&p1->p_klist)) {
535 mutex_exit(proc_lock);
536 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
537 mutex_enter(proc_lock);
538 }
539
540 /*
541 * Make child runnable, set start time, and add to run queue except
542 * if the parent requested the child to start in SSTOP state.
543 */
544 mutex_enter(p2->p_lock);
545
546 /*
547 * Start profiling.
548 */
549 if ((p2->p_stflag & PST_PROFIL) != 0) {
550 mutex_spin_enter(&p2->p_stmutex);
551 startprofclock(p2);
552 mutex_spin_exit(&p2->p_stmutex);
553 }
554
555 getmicrotime(&p2->p_stats->p_start);
556 p2->p_acflag = AFORK;
557 lwp_lock(l2);
558 KASSERT(p2->p_nrlwps == 1);
559 if (p2->p_sflag & PS_STOPFORK) {
560 struct schedstate_percpu *spc = &l2->l_cpu->ci_schedstate;
561 p2->p_nrlwps = 0;
562 p2->p_stat = SSTOP;
563 p2->p_waited = 0;
564 p1->p_nstopchild++;
565 l2->l_stat = LSSTOP;
566 KASSERT(l2->l_wchan == NULL);
567 lwp_unlock_to(l2, spc->spc_lwplock);
568 } else {
569 p2->p_nrlwps = 1;
570 p2->p_stat = SACTIVE;
571 l2->l_stat = LSRUN;
572 sched_enqueue(l2, false);
573 lwp_unlock(l2);
574 }
575
576 /*
577 * Return child pid to parent process,
578 * marking us as parent via retval[1].
579 */
580 if (retval != NULL) {
581 retval[0] = p2->p_pid;
582 retval[1] = 0;
583 }
584 mutex_exit(p2->p_lock);
585
586 /*
587 * Preserve synchronization semantics of vfork. If waiting for
588 * child to exec or exit, sleep until it clears LP_VFORKWAIT.
589 */
590 #if 0
591 while (l1->l_pflag & LP_VFORKWAIT) {
592 cv_wait(&l1->l_waitcv, proc_lock);
593 }
594 #else
595 while (p2->p_lflag & PL_PPWAIT)
596 cv_wait(&p1->p_waitcv, proc_lock);
597 #endif
598
599 /*
600 * Let the parent know that we are tracing its child.
601 */
602 if (tracefork) {
603 ksiginfo_t ksi;
604
605 KSI_INIT_EMPTY(&ksi);
606 ksi.ksi_signo = SIGTRAP;
607 ksi.ksi_lid = l1->l_lid;
608 kpsignal(p1, &ksi, NULL);
609 }
610 mutex_exit(proc_lock);
611
612 return 0;
613 }
614