sys/kern/kern_ktrace.c

   1 /*
   2  * Copyright (c) 1989, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  *      @(#)kern_ktrace.c       8.2 (Berkeley) 9/23/93
  30  * $FreeBSD: src/sys/kern/kern_ktrace.c,v 1.35.2.6 2002/07/05 22:36:38 darrenr Exp $
  31  */
  32
  33 #include "opt_ktrace.h"
  34
  35 #include <sys/param.h>
  36 #include <sys/systm.h>
  37 #include <sys/uio.h>
  38 #include <sys/sysmsg.h>
  39 #include <sys/kernel.h>
  40 #include <sys/proc.h>
  41 #include <sys/fcntl.h>
  42 #include <sys/lock.h>
  43 #include <sys/nlookup.h>
  44 #include <sys/vnode.h>
  45 #include <sys/ktrace.h>
  46 #include <sys/malloc.h>
  47 #include <sys/sysctl.h>
  48 #include <sys/syslog.h>
  49 #include <sys/sysent.h>
  50
  51 #include <vm/vm_zone.h>
  52
  53 static MALLOC_DEFINE(M_KTRACE, "KTRACE", "KTRACE");
  54
  55 #ifdef KTRACE
  56 static void ktrgetheader (struct ktr_header *kth, int type);
  57 static struct ktr_syscall *ktrgetsyscall(struct ktr_header *kth,
  58                                 struct ktr_syscall *ktp_cache, int narg);
  59 static void ktrputsyscall(struct ktr_syscall *ktp_cache,
  60                                 struct ktr_syscall *ktp);
  61 static void ktrwrite (struct lwp *, struct ktr_header *, struct uio *);
  62 static int ktrcanset (struct thread *,struct proc *);
  63 static int ktrsetchildren (struct thread *, struct proc *,
  64                                 int, int, ktrace_node_t);
  65 static int ktrops (struct thread *,struct proc *,int,int, ktrace_node_t);
  66
  67 /*
  68  * MPSAFE
  69  */
  70 static
  71 void
  72 ktrgetheader(struct ktr_header *kth, int type)
  73 {
  74         thread_t td = curthread;
  75         struct proc *p = td->td_proc;
  76         struct lwp *lp = td->td_lwp;
  77
  78         kth->ktr_type = type;
  79         /* XXX threaded flag is a hack at the moment */
  80         kth->ktr_flags = (p->p_nthreads > 1) ? KTRH_THREADED : 0;
  81         kth->ktr_flags |= KTRH_CPUID_ENCODE(td->td_gd->gd_cpuid);
  82         /*microtime(&kth->ktr_time); set in ktrwrite */
  83         kth->ktr_pid = p->p_pid;
  84         kth->ktr_tid = lp->lwp_tid;
  85         bcopy(p->p_comm, kth->ktr_comm, MAXCOMLEN + 1);
  86 }
  87
  88 static
  89 struct ktr_syscall *
  90 ktrgetsyscall(struct ktr_header *kth, struct ktr_syscall *ktp_cache, int narg)
  91 {
  92         size_t len;
  93
  94         len = offsetof(struct ktr_syscall, ktr_args[narg]);
  95         if (len > sizeof(*ktp_cache))
  96                 ktp_cache = kmalloc(len, M_KTRACE, M_WAITOK);
  97         kth->ktr_buf = (caddr_t)ktp_cache;
  98         kth->ktr_len = (int)len;
  99         return (ktp_cache);
 100 }
 101
 102 static
 103 void
 104 ktrputsyscall(struct ktr_syscall *ktp_cache, struct ktr_syscall *ktp)
 105 {
 106         if (ktp != ktp_cache)
 107                 kfree(ktp, M_KTRACE);
 108 }
 109
 110 void
 111 ktrsyscall(struct lwp *lp, int code, int narg, union sysunion *uap)
 112 {
 113         struct ktr_header kth;
 114         struct ktr_syscall ktp_cache;
 115         struct ktr_syscall *ktp;
 116         register_t *argp;
 117         register_t *args = (void *)uap;
 118         int i;
 119
 120         /*
 121          * Setting the active bit prevents a ktrace recursion from the
 122          * ktracing op itself.
 123          */
 124         lp->lwp_traceflag |= KTRFAC_ACTIVE;
 125         ktrgetheader(&kth, KTR_SYSCALL);
 126
 127         ktp = ktrgetsyscall(&kth, &ktp_cache, narg);
 128         ktp->ktr_code = code;
 129         ktp->ktr_narg = narg;
 130         argp = &ktp->ktr_args[0];
 131         for (i = 0; i < narg; i++)
 132                 *argp++ = args[i];
 133         ktrwrite(lp, &kth, NULL);
 134
 135         ktrputsyscall(&ktp_cache, ktp);
 136         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
 137 }
 138
 139 void
 140 ktrsysret(struct lwp *lp, int code, int error, register_t retval)
 141 {
 142         struct ktr_header kth;
 143         struct ktr_sysret ktp;
 144
 145         lp->lwp_traceflag |= KTRFAC_ACTIVE;
 146         ktrgetheader(&kth, KTR_SYSRET);
 147
 148         ktp.ktr_code = code;
 149         ktp.ktr_error = error;
 150         if (error == 0)
 151                 ktp.ktr_retval = retval;                /* what about val2 ? */
 152         else
 153                 ktp.ktr_retval = 0;
 154
 155         kth.ktr_buf = (caddr_t)&ktp;
 156         kth.ktr_len = (int)sizeof(struct ktr_sysret);
 157
 158         ktrwrite(lp, &kth, NULL);
 159         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
 160 }
 161
 162 void
 163 ktrnamei(struct lwp *lp, char *path)
 164 {
 165         struct ktr_header kth;
 166
 167         lp->lwp_traceflag |= KTRFAC_ACTIVE;
 168         ktrgetheader(&kth, KTR_NAMEI);
 169
 170         kth.ktr_len = (int)strlen(path);
 171         kth.ktr_buf = path;
 172
 173         ktrwrite(lp, &kth, NULL);
 174         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
 175 }
 176
 177 void
 178 ktrsysctl(struct lwp *lp, int *name, u_int namelen)
 179 {
 180         struct ktr_header kth;
 181         u_int mib[CTL_MAXNAME + 2];
 182         char *mibname;
 183         size_t mibnamelen;
 184         int error;
 185
 186         lp->lwp_traceflag |= KTRFAC_ACTIVE;
 187         /* Lookup name of mib. */
 188         KASSERT(namelen <= CTL_MAXNAME, ("sysctl MIB too long"));
 189         mib[0] = 0;
 190         mib[1] = 1;
 191         bcopy(name, mib + 2, namelen * sizeof(*name));
 192         mibnamelen = 128;
 193         mibname = kmalloc(mibnamelen, M_KTRACE, M_WAITOK);
 194         error = kernel_sysctl(mib, namelen + 2, mibname, &mibnamelen,
 195             NULL, 0, &mibnamelen);
 196         if (error) {
 197                 kfree(mibname, M_KTRACE);
 198                 lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
 199                 return;
 200         }
 201         ktrgetheader(&kth, KTR_SYSCTL);
 202         kth.ktr_len = mibnamelen;
 203         kth.ktr_buf = mibname;
 204         ktrwrite(lp, &kth, NULL);
 205         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
 206 }
 207
 208 void
 209 ktrgenio(struct lwp *lp, int fd, enum uio_rw rw, struct uio *uio, int error)
 210 {
 211         struct ktr_header kth;
 212         struct ktr_genio ktg;
 213
 214         if (error)
 215                 return;
 216         lp->lwp_traceflag |= KTRFAC_ACTIVE;
 217         ktrgetheader(&kth, KTR_GENIO);
 218
 219         ktg.ktr_fd = fd;
 220         ktg.ktr_rw = rw;
 221         kth.ktr_buf = (caddr_t)&ktg;
 222         kth.ktr_len = (int)sizeof(struct ktr_genio);
 223         uio->uio_offset = 0;
 224         uio->uio_rw = UIO_WRITE;
 225
 226         ktrwrite(lp, &kth, uio);
 227         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
 228 }
 229
 230 void
 231 ktrpsig(struct lwp *lp, int sig, sig_t action, sigset_t *mask, int code)
 232 {
 233         struct ktr_header kth;
 234         struct ktr_psig kp;
 235
 236         lp->lwp_traceflag |= KTRFAC_ACTIVE;
 237         ktrgetheader(&kth, KTR_PSIG);
 238
 239         kp.signo = (char)sig;
 240         kp.action = action;
 241         kp.mask = *mask;
 242         kp.code = code;
 243         kth.ktr_buf = (caddr_t)&kp;
 244         kth.ktr_len = (int)sizeof(struct ktr_psig);
 245
 246         ktrwrite(lp, &kth, NULL);
 247         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
 248 }
 249
 250 void
 251 ktrcsw(struct lwp *lp, int out, int user)
 252 {
 253         struct ktr_header kth;
 254         struct ktr_csw kc;
 255
 256         lp->lwp_traceflag |= KTRFAC_ACTIVE;
 257         ktrgetheader(&kth, KTR_CSW);
 258
 259         kc.out = out;
 260         kc.user = user;
 261         kth.ktr_buf = (caddr_t)&kc;
 262         kth.ktr_len = (int)sizeof(struct ktr_csw);
 263
 264         ktrwrite(lp, &kth, NULL);
 265         lp->lwp_traceflag &= ~KTRFAC_ACTIVE;
 266 }
 267 #endif
 268
 269 /* Interface and common routines */
 270
 271 #ifdef KTRACE
 272 /*
 273  * ktrace system call
 274  */
 275 struct ktrace_clear_info {
 276         ktrace_node_t tracenode;
 277         int rootclear;
 278         int error;
 279 };
 280
 281 static int ktrace_clear_callback(struct proc *p, void *data);
 282
 283 #endif
 284
 285 /*
 286  * MPALMOSTSAFE
 287  */
 288 int
 289 sys_ktrace(struct sysmsg *sysmsg, const struct ktrace_args *uap)
 290 {
 291 #ifdef KTRACE
 292         struct ktrace_clear_info info;
 293         struct thread *td = curthread;
 294         struct proc *curp = td->td_proc;
 295         struct proc *p;
 296         struct pgrp *pg;
 297         int facs = uap->facs & ~KTRFAC_ROOT;
 298         int ops = KTROP(uap->ops);
 299         int descend = uap->ops & KTRFLAG_DESCEND;
 300         int ret = 0;
 301         int error = 0;
 302         struct nlookupdata nd;
 303         ktrace_node_t tracenode = NULL;
 304
 305         lwkt_gettoken(&curp->p_token);
 306         curp->p_traceflag |= KTRFAC_ACTIVE;
 307
 308         if (ops != KTROP_CLEAR) {
 309                 /*
 310                  * an operation which requires a file argument.
 311                  */
 312                 error = nlookup_init(&nd, uap->fname,
 313                                         UIO_USERSPACE, NLC_LOCKVP);
 314                 if (error == 0)
 315                         error = vn_open(&nd, NULL, FREAD|FWRITE|O_NOFOLLOW, 0);
 316                 if (error == 0 && nd.nl_open_vp->v_type != VREG)
 317                         error = EACCES;
 318                 if (error) {
 319                         curp->p_traceflag &= ~KTRFAC_ACTIVE;
 320                         nlookup_done(&nd);
 321                         goto done;
 322                 }
 323                 tracenode = kmalloc(sizeof(struct ktrace_node), M_KTRACE,
 324                                     M_WAITOK | M_ZERO);
 325                 tracenode->kn_vp = nd.nl_open_vp;
 326                 tracenode->kn_refs = 1;
 327                 nd.nl_open_vp = NULL;
 328                 nlookup_done(&nd);
 329                 vn_unlock(tracenode->kn_vp);
 330         }
 331         /*
 332          * Clear all uses of the tracefile.  Not the most efficient operation
 333          * in the world.
 334          */
 335         if (ops == KTROP_CLEARFILE) {
 336                 info.tracenode = tracenode;
 337                 info.error = 0;
 338                 info.rootclear = 0;
 339                 allproc_scan(ktrace_clear_callback, &info, 0);
 340                 error = info.error;
 341                 goto done;
 342         }
 343         /*
 344          * need something to (un)trace (XXX - why is this here?)
 345          */
 346         if (!facs) {
 347                 error = EINVAL;
 348                 goto done;
 349         }
 350         /*
 351          * do it
 352          */
 353         if (uap->pid < 0) {
 354                 /*
 355                  * By process group.  Process group is referenced, preventing
 356                  * disposal.
 357                  */
 358                 pg = pgfind(-uap->pid);
 359                 if (pg == NULL) {
 360                         error = ESRCH;
 361                         goto done;
 362                 }
 363                 lwkt_gettoken(&pg->pg_token);
 364                 LIST_FOREACH(p, &pg->pg_members, p_pglist) {
 365                         PHOLD(p);
 366                         if (descend)
 367                                 ret |= ktrsetchildren(td, p, ops, facs, tracenode);
 368                         else
 369                                 ret |= ktrops(td, p, ops, facs, tracenode);
 370                         PRELE(p);
 371                 }
 372                 lwkt_reltoken(&pg->pg_token);
 373                 pgrel(pg);
 374         } else {
 375                 /*
 376                  * by pid
 377                  */
 378                 p = pfind(uap->pid);
 379                 if (p == NULL) {
 380                         error = ESRCH;
 381                         goto done;
 382                 }
 383                 if (descend)
 384                         ret |= ktrsetchildren(td, p, ops, facs, tracenode);
 385                 else
 386                         ret |= ktrops(td, p, ops, facs, tracenode);
 387                 PRELE(p);
 388         }
 389         if (!ret)
 390                 error = EPERM;
 391 done:
 392         if (tracenode)
 393                 ktrdestroy(&tracenode);
 394         curp->p_traceflag &= ~KTRFAC_ACTIVE;
 395         lwkt_reltoken(&curp->p_token);
 396         return (error);
 397 #else
 398         return ENOSYS;
 399 #endif
 400 }
 401
 402 #ifdef KTRACE
 403
 404 /*
 405  * NOTE: NOT MPSAFE (yet)
 406  */
 407 static int
 408 ktrace_clear_callback(struct proc *p, void *data)
 409 {
 410         struct ktrace_clear_info *info = data;
 411
 412         if (p->p_tracenode) {
 413                 if (info->rootclear) {
 414                         if (p->p_tracenode == info->tracenode) {
 415                                 ktrdestroy(&p->p_tracenode);
 416                                 p->p_traceflag = 0;
 417                         }
 418                 } else {
 419                         if (p->p_tracenode->kn_vp == info->tracenode->kn_vp) {
 420                                 if (ktrcanset(curthread, p)) {
 421                                         ktrdestroy(&p->p_tracenode);
 422                                         p->p_traceflag = 0;
 423                                 } else {
 424                                         info->error = EPERM;
 425                                 }
 426                         }
 427                 }
 428         }
 429         return(0);
 430 }
 431
 432 #endif
 433
 434 /*
 435  * utrace system call
 436  *
 437  * MPALMOSTSAFE
 438  */
 439 int
 440 sys_utrace(struct sysmsg *sysmsg, const struct utrace_args *uap)
 441 {
 442 #ifdef KTRACE
 443         struct ktr_header kth;
 444         struct thread *td = curthread;  /* XXX */
 445         char cp_cache[64];
 446         caddr_t cp;
 447
 448         if (!KTRPOINT(td, KTR_USER))
 449                 return (0);
 450         if (uap->len > KTR_USER_MAXLEN)
 451                 return (EINVAL);
 452         td->td_lwp->lwp_traceflag |= KTRFAC_ACTIVE;
 453         ktrgetheader(&kth, KTR_USER);
 454         if (uap->len <= sizeof(cp_cache))
 455                 cp = cp_cache;
 456         else
 457                 cp = kmalloc(uap->len, M_KTRACE, M_WAITOK);
 458
 459         if (!copyin(uap->addr, cp, uap->len)) {
 460                 kth.ktr_buf = cp;
 461                 kth.ktr_len = uap->len;
 462                 ktrwrite(td->td_lwp, &kth, NULL);
 463         }
 464         if (cp != cp_cache)
 465                 kfree(cp, M_KTRACE);
 466         td->td_lwp->lwp_traceflag &= ~KTRFAC_ACTIVE;
 467
 468         return (0);
 469 #else
 470         return (ENOSYS);
 471 #endif
 472 }
 473
 474 void
 475 ktrdestroy(struct ktrace_node **tracenodep)
 476 {
 477         ktrace_node_t tracenode;
 478
 479         if ((tracenode = *tracenodep) != NULL) {
 480                 *tracenodep = NULL;
 481                 KKASSERT(tracenode->kn_refs > 0);
 482                 if (atomic_fetchadd_int(&tracenode->kn_refs, -1) == 1) {
 483                         vn_close(tracenode->kn_vp, FREAD|FWRITE, NULL);
 484                         tracenode->kn_vp = NULL;
 485                         kfree(tracenode, M_KTRACE);
 486                 }
 487         }
 488 }
 489
 490 /*
 491  * This allows a process to inherit a ref on a tracenode and is also used
 492  * as a temporary ref to prevent a tracenode from being destroyed out from
 493  * under an active operation.
 494  */
 495 ktrace_node_t
 496 ktrinherit(ktrace_node_t tracenode)
 497 {
 498         if (tracenode) {
 499                 KKASSERT(tracenode->kn_refs > 0);
 500                 atomic_add_int(&tracenode->kn_refs, 1);
 501         }
 502         return(tracenode);
 503 }
 504
 505 #ifdef KTRACE
 506 static int
 507 ktrops(struct thread *td, struct proc *p, int ops, int facs,
 508        ktrace_node_t tracenode)
 509 {
 510         ktrace_node_t oldnode;
 511
 512         if (!ktrcanset(td, p))
 513                 return (0);
 514         if (ops == KTROP_SET) {
 515                 if ((oldnode = p->p_tracenode) != tracenode) {
 516                         p->p_tracenode = ktrinherit(tracenode);
 517                         ktrdestroy(&oldnode);
 518                 }
 519                 p->p_traceflag |= facs;
 520                 if (td->td_ucred->cr_uid == 0)
 521                         p->p_traceflag |= KTRFAC_ROOT;
 522         } else {
 523                 /* KTROP_CLEAR */
 524                 if (((p->p_traceflag &= ~facs) & KTRFAC_MASK) == 0) {
 525                         /* no more tracing */
 526                         p->p_traceflag = 0;
 527                         ktrdestroy(&p->p_tracenode);
 528                 }
 529         }
 530
 531         return (1);
 532 }
 533
 534 static int
 535 ktrsetchildren(struct thread *td, struct proc *top, int ops, int facs,
 536                ktrace_node_t tracenode)
 537 {
 538         struct proc *p;
 539         struct proc *np;
 540         int ret = 0;
 541
 542         p = top;
 543         PHOLD(p);
 544         lwkt_gettoken(&p->p_token);
 545
 546         for (;;) {
 547                 ret |= ktrops(td, p, ops, facs, tracenode);
 548
 549                 /*
 550                  * If this process has children, descend to them next,
 551                  * otherwise do any siblings, and if done with this level,
 552                  * follow back up the tree (but not past top).
 553                  */
 554                 if ((np = LIST_FIRST(&p->p_children)) != NULL) {
 555                         PHOLD(np);
 556                 }
 557                 while (np == NULL) {
 558                         if (p == top)
 559                                 break;
 560                         if ((np = LIST_NEXT(p, p_sibling)) != NULL) {
 561                                 PHOLD(np);
 562                                 break;
 563                         }
 564
 565                         /*
 566                          * recurse up to parent, set p in our inner
 567                          * loop when doing this.  np can be NULL if
 568                          * we race a reparenting to init (thus 'top'
 569                          * is skipped past and never encountered).
 570                          */
 571                         np = p->p_pptr;
 572                         if (np == NULL)
 573                                 break;
 574                         PHOLD(np);
 575                         lwkt_reltoken(&p->p_token);
 576                         PRELE(p);
 577                         p = np;
 578                         lwkt_gettoken(&p->p_token);
 579                         np = NULL;
 580                 }
 581                 lwkt_reltoken(&p->p_token);
 582                 PRELE(p);
 583                 p = np;
 584                 if (p == NULL)
 585                         break;
 586                 /* Already held, but we need the token too */
 587                 lwkt_gettoken(&p->p_token);
 588         }
 589         return (ret);
 590 }
 591
 592 static void
 593 ktrwrite(struct lwp *lp, struct ktr_header *kth, struct uio *uio)
 594 {
 595         struct ktrace_clear_info info;
 596         struct uio auio;
 597         struct iovec aiov[2];
 598         int error;
 599         ktrace_node_t tracenode;
 600
 601         /*
 602          * We have to ref our tracenode to prevent it from being ripped out
 603          * from under us while we are trying to use it.   p_tracenode can
 604          * go away at any time if another process gets a write error.
 605          *
 606          * XXX not MP safe
 607          */
 608         if (lp->lwp_proc->p_tracenode == NULL)
 609                 return;
 610         tracenode = ktrinherit(lp->lwp_proc->p_tracenode);
 611         auio.uio_iov = &aiov[0];
 612         auio.uio_offset = 0;
 613         auio.uio_segflg = UIO_SYSSPACE;
 614         auio.uio_rw = UIO_WRITE;
 615         aiov[0].iov_base = (caddr_t)kth;
 616         aiov[0].iov_len = sizeof(struct ktr_header);
 617         auio.uio_resid = sizeof(struct ktr_header);
 618         auio.uio_iovcnt = 1;
 619         auio.uio_td = curthread;
 620         if (kth->ktr_len > 0) {
 621                 auio.uio_iovcnt++;
 622                 aiov[1].iov_base = kth->ktr_buf;
 623                 aiov[1].iov_len = kth->ktr_len;
 624                 auio.uio_resid += kth->ktr_len;
 625                 if (uio != NULL)
 626                         kth->ktr_len += uio->uio_resid;
 627         }
 628
 629         /*
 630          * NOTE: Must set timestamp after obtaining lock to ensure no
 631          *       timestamp reversals in the output file.
 632          */
 633         vn_lock(tracenode->kn_vp, LK_EXCLUSIVE | LK_RETRY);
 634         microtime(&kth->ktr_time);
 635         error = VOP_WRITE(tracenode->kn_vp, &auio,
 636                           IO_UNIT | IO_APPEND, lp->lwp_thread->td_ucred);
 637         if (error == 0 && uio != NULL) {
 638                 error = VOP_WRITE(tracenode->kn_vp, uio,
 639                               IO_UNIT | IO_APPEND, lp->lwp_thread->td_ucred);
 640         }
 641         vn_unlock(tracenode->kn_vp);
 642         if (error) {
 643                 /*
 644                  * If an error occured, give up tracing on all processes
 645                  * using this tracenode.  This is not MP safe but is
 646                  * blocking-safe.
 647                  */
 648                 log(LOG_NOTICE,
 649                     "ktrace write failed, errno %d, tracing stopped\n", error);
 650                 info.tracenode = tracenode;
 651                 info.error = 0;
 652                 info.rootclear = 1;
 653                 allproc_scan(ktrace_clear_callback, &info, 0);
 654         }
 655         ktrdestroy(&tracenode);
 656 }
 657
 658 /*
 659  * Return true if caller has permission to set the ktracing state
 660  * of target.  Essentially, the target can't possess any
 661  * more permissions than the caller.  KTRFAC_ROOT signifies that
 662  * root previously set the tracing status on the target process, and
 663  * so, only root may further change it.
 664  *
 665  * TODO: check groups.  use caller effective gid.
 666  */
 667 static int
 668 ktrcanset(struct thread *calltd, struct proc *targetp)
 669 {
 670         struct ucred *caller = calltd->td_ucred;
 671         struct ucred *target = targetp->p_ucred;
 672
 673         if (!PRISON_CHECK(caller, target))
 674                 return (0);
 675         if ((caller->cr_uid == target->cr_ruid &&
 676              target->cr_ruid == target->cr_svuid &&
 677              caller->cr_rgid == target->cr_rgid &&      /* XXX */
 678              target->cr_rgid == target->cr_svgid &&
 679              (targetp->p_traceflag & KTRFAC_ROOT) == 0 &&
 680              (targetp->p_flags & P_SUGID) == 0) ||
 681              caller->cr_uid == 0)
 682                 return (1);
 683
 684         return (0);
 685 }
 686
 687 #endif /* KTRACE */