trace/trace.c

   1 /*
   2  * Copyright (C) 2015 John Crispin <blogic@openwrt.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU Lesser General Public License version 2.1
   6  * as published by the Free Software Foundation
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  */
  13
  14 #define _GNU_SOURCE
  15 #include <fcntl.h>
  16 #include <stddef.h>
  17 #include <sys/ptrace.h>
  18 #include <sys/stat.h>
  19 #include <sys/types.h>
  20 #include <sys/user.h>
  21 #include <sys/wait.h>
  22 #include <unistd.h>
  23 #include <stdlib.h>
  24 #include <stdio.h>
  25 #include <errno.h>
  26 #include <string.h>
  27 #include <syslog.h>
  28 #include <limits.h>
  29
  30 #ifndef PTRACE_EVENT_STOP
  31 /* PTRACE_EVENT_STOP is defined in linux/ptrace.h, but this header
  32  * collides with musl's sys/ptrace.h */
  33 #define PTRACE_EVENT_STOP 128
  34 #endif
  35
  36 #ifndef PTRACE_EVENT_SECCOMP
  37 /* undefined with uClibc-ng */
  38 #define PTRACE_EVENT_SECCOMP 7
  39 #endif
  40
  41 #include <libubox/ulog.h>
  42 #include <libubox/uloop.h>
  43 #include <libubox/blobmsg.h>
  44 #include <libubox/blobmsg_json.h>
  45
  46 #include "../syscall-names.h"
  47
  48 #define _offsetof(a, b) __builtin_offsetof(a,b)
  49 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
  50
  51 #if defined (__aarch64__)
  52 #include <linux/ptrace.h>
  53 #elif defined(__amd64__)
  54 #define reg_syscall_nr  _offsetof(struct user, regs.orig_rax)
  55 #elif defined(__arm__)
  56 #include <asm/ptrace.h>         /* for PTRACE_SET_SYSCALL */
  57 #define reg_syscall_nr  _offsetof(struct user, regs.uregs[7])
  58 # if defined(__ARM_EABI__)
  59 # define reg_retval_nr  _offsetof(struct user, regs.uregs[0])
  60 # endif
  61 #elif defined(__i386__)
  62 #define reg_syscall_nr  _offsetof(struct user, regs.orig_eax)
  63 #elif defined(__mips)
  64 # ifndef EF_REG2
  65 # define EF_REG2        8
  66 # endif
  67 #define reg_syscall_nr  (EF_REG2 / 4)
  68 #elif defined(__PPC__)
  69 #define reg_syscall_nr  _offsetof(struct user, regs.gpr[0])
  70 #define reg_retval_nr   _offsetof(struct user, regs.gpr[3])
  71 #else
  72 #error tracing is not supported on this architecture
  73 #endif
  74
  75 enum mode {
  76         UTRACE,
  77         SECCOMP_TRACE,
  78 } mode = UTRACE;
  79
  80 struct tracee {
  81         struct uloop_process proc;
  82         int in_syscall;
  83 };
  84
  85 static struct tracee tracer;
  86 static int syscall_count[SYSCALL_COUNT];
  87 static int violation_count;
  88 static struct blob_buf b;
  89 static int debug;
  90 char *json = NULL;
  91 int ptrace_restart;
  92
  93 static void set_syscall(const char *name, int val)
  94 {
  95         int i;
  96
  97         for (i = 0; i < SYSCALL_COUNT; i++) {
  98                 int sc = syscall_index_to_number(i);
  99                 if (syscall_name(sc) && !strcmp(syscall_name(sc), name)) {
 100                         syscall_count[i] = val;
 101                         return;
 102                 }
 103         }
 104 }
 105
 106 struct syscall {
 107         int syscall;
 108         int count;
 109 };
 110
 111 static int cmp_count(const void *a, const void *b)
 112 {
 113         return ((struct syscall*)b)->count - ((struct syscall*)a)->count;
 114 }
 115
 116 static void print_syscalls(int policy, const char *json)
 117 {
 118         void *c, *d, *e;
 119         int i;
 120         char *tmp;
 121
 122         if (mode == UTRACE) {
 123                 set_syscall("rt_sigaction", 1);
 124                 set_syscall("sigreturn", 1);
 125                 set_syscall("rt_sigreturn", 1);
 126                 set_syscall("exit_group", 1);
 127                 set_syscall("exit", 1);
 128         }
 129
 130         struct syscall sorted[SYSCALL_COUNT];
 131
 132         for (i = 0; i < SYSCALL_COUNT; i++) {
 133                 sorted[i].syscall = syscall_index_to_number(i);
 134                 sorted[i].count = syscall_count[i];
 135         }
 136
 137         qsort(sorted, SYSCALL_COUNT, sizeof(sorted[0]), cmp_count);
 138
 139         blob_buf_init(&b, 0);
 140         blobmsg_add_string(&b, "defaultAction", "SCMP_ACT_KILL_PROCESS");
 141         c = blobmsg_open_array(&b, "syscalls");
 142         d = blobmsg_open_table(&b, "");
 143         e = blobmsg_open_array(&b, "names");
 144
 145         for (i = 0; i < SYSCALL_COUNT; i++) {
 146                 int sc = sorted[i].syscall;
 147                 if (!sorted[i].count)
 148                         break;
 149                 if (syscall_name(sc)) {
 150                         if (debug)
 151                                 printf("syscall %d (%s) was called %d times\n",
 152                                        sc, syscall_name(sc), sorted[i].count);
 153                         blobmsg_add_string(&b, NULL, syscall_name(sc));
 154                 } else {
 155                         ULOG_ERR("no name found for syscall(%d)\n", sc);
 156                 }
 157         }
 158         blobmsg_close_array(&b, e);
 159         blobmsg_add_string(&b, "action", "SCMP_ACT_ALLOW");
 160         blobmsg_close_table(&b, d);
 161         blobmsg_close_array(&b, c);
 162         if (json) {
 163                 FILE *fp = fopen(json, "w");
 164                 if (fp) {
 165                         fprintf(fp, "%s\n", blobmsg_format_json_indent(b.head, true, 0));
 166                         fclose(fp);
 167                         ULOG_INFO("saving syscall trace to %s\n", json);
 168                 } else {
 169                         ULOG_ERR("failed to open %s\n", json);
 170                 }
 171         } else {
 172                 tmp = blobmsg_format_json_indent(b.head, true, 0);
 173                 if (!tmp)
 174                         return;
 175
 176                 printf("%s\n", tmp);
 177                 free(tmp);
 178         }
 179
 180 }
 181
 182 static void report_seccomp_vialation(pid_t pid, unsigned syscall)
 183 {
 184         char buf[200];
 185         snprintf(buf, sizeof(buf), "/proc/%d/cmdline", pid);
 186         int f = open(buf, O_RDONLY);
 187         int r = read(f, buf, sizeof(buf) - 1);
 188         if (r >= 0)
 189                 buf[r] = 0;
 190         else
 191                 strcpy(buf, "unknown?");
 192         close(f);
 193
 194         if (violation_count < INT_MAX)
 195                 violation_count++;
 196         int i = syscall_index(syscall);
 197         if (i >= 0) {
 198                 syscall_count[i]++;
 199                 ULOG_ERR("%s[%u] tried to call non-whitelisted syscall: %s (see %s)\n",
 200                          buf, pid,  syscall_name(syscall), json);
 201         } else {
 202                 ULOG_ERR("%s[%u] tried to call non-whitelisted syscall: %d (see %s)\n",
 203                          buf, pid,  syscall, json);
 204         }
 205 }
 206
 207 static void tracer_cb(struct uloop_process *c, int ret)
 208 {
 209         struct tracee *tracee = container_of(c, struct tracee, proc);
 210         int inject_signal = 0;
 211
 212         /* We explicitely check for events in upper 16 bits, because
 213          * musl (as opposed to glibc) does not report
 214          * PTRACE_EVENT_STOP as WIFSTOPPED */
 215         if (WIFSTOPPED(ret) || (ret >> 16)) {
 216                 if (WSTOPSIG(ret) & 0x80) {
 217                         if (!tracee->in_syscall) {
 218 #ifdef __aarch64__
 219                                 int syscall = -1;
 220                                 struct ptrace_syscall_info ptsi = {.op=PTRACE_SYSCALL_INFO_ENTRY};
 221                                 if (ptrace(PTRACE_GET_SYSCALL_INFO, c->pid, sizeof(ptsi), &ptsi) != -1)
 222                                         syscall = ptsi.entry.nr;
 223 #else
 224                                 int syscall = ptrace(PTRACE_PEEKUSER, c->pid, reg_syscall_nr);
 225 #endif
 226                                 int i = syscall_index(syscall);
 227                                 if (i >= 0) {
 228                                         syscall_count[i]++;
 229                                         if (debug)
 230                                                 fprintf(stderr, "%s()\n", syscall_name(syscall));
 231                                 } else if (debug) {
 232                                         fprintf(stderr, "syscal(%d)\n", syscall);
 233                                 }
 234                         }
 235                         tracee->in_syscall = !tracee->in_syscall;
 236                 } else if ((ret >> 8) == (SIGTRAP | (PTRACE_EVENT_FORK << 8)) ||
 237                            (ret >> 8) == (SIGTRAP | (PTRACE_EVENT_VFORK << 8)) ||
 238                            (ret >> 8) == (SIGTRAP | (PTRACE_EVENT_CLONE << 8))) {
 239                         struct tracee *child = calloc(1, sizeof(struct tracee));
 240
 241                         unsigned long msg;
 242                         ptrace(PTRACE_GETEVENTMSG, c->pid, 0, &msg);
 243                         child->proc.pid = msg;
 244                         child->proc.cb = tracer_cb;
 245                         ptrace(ptrace_restart, child->proc.pid, 0, 0);
 246                         uloop_process_add(&child->proc);
 247                         if (debug)
 248                                 fprintf(stderr, "Tracing new child %d\n", child->proc.pid);
 249                 } else if ((ret >> 16) == PTRACE_EVENT_STOP) {
 250                         /* Nothing special to do here */
 251                 } else if ((ret >> 8) == (SIGTRAP | (PTRACE_EVENT_SECCOMP << 8))) {
 252 #ifdef __aarch64__
 253                         int syscall = -1;
 254                         struct ptrace_syscall_info ptsi = {.op=PTRACE_SYSCALL_INFO_SECCOMP};
 255                         if (ptrace(PTRACE_GET_SYSCALL_INFO, c->pid, sizeof(ptsi), &ptsi) != -1)
 256                                 syscall = ptsi.entry.nr;
 257 #else
 258                         int syscall = ptrace(PTRACE_PEEKUSER, c->pid, reg_syscall_nr);
 259 #if defined(__arm__)
 260                         ptrace(PTRACE_SET_SYSCALL, c->pid, 0, -1);
 261                         ptrace(PTRACE_POKEUSER, c->pid, reg_retval_nr, -ENOSYS);
 262 #else
 263                         ptrace(PTRACE_POKEUSER, c->pid, reg_syscall_nr, -1);
 264 #endif
 265 #endif
 266                         report_seccomp_vialation(c->pid, syscall);
 267                 } else {
 268                         inject_signal = WSTOPSIG(ret);
 269                         if (debug)
 270                                 fprintf(stderr, "Injecting signal %d into pid %d\n",
 271                                         inject_signal, tracee->proc.pid);
 272                 }
 273         } else if (WIFEXITED(ret) || (WIFSIGNALED(ret) && WTERMSIG(ret))) {
 274                 if (tracee == &tracer) {
 275                         uloop_end(); /* Main process exit */
 276                 } else {
 277                         if (debug)
 278                                 fprintf(stderr, "Child %d exited\n", tracee->proc.pid);
 279                         free(tracee);
 280                 }
 281                 return;
 282         }
 283
 284         ptrace(ptrace_restart, c->pid, 0, inject_signal);
 285         uloop_process_add(c);
 286 }
 287
 288 static void sigterm_handler(int signum)
 289 {
 290         /* When we receive SIGTERM, we forward it to the tracee. After
 291          * the tracee exits, trace_cb() will be called and make us
 292          * exit too. */
 293         kill(tracer.proc.pid, SIGTERM);
 294 }
 295
 296
 297 int main(int argc, char **argv, char **envp)
 298 {
 299         int status, ch, policy = EPERM;
 300         pid_t child;
 301
 302         /* When invoked via seccomp-trace symlink, work as seccomp
 303          * violation logger rather than as syscall tracer */
 304         if (strstr(argv[0], "seccomp-trace"))
 305                 mode = SECCOMP_TRACE;
 306
 307         while ((ch = getopt(argc, argv, "f:p:")) != -1) {
 308                 switch (ch) {
 309                 case 'f':
 310                         json = optarg;
 311                         break;
 312                 case 'p':
 313                         policy = atoi(optarg);
 314                         break;
 315                 }
 316         }
 317
 318         if (!json)
 319                 json = getenv("SECCOMP_FILE");
 320
 321         argc -= optind;
 322         argv += optind;
 323
 324         if (!argc)
 325                 return -1;
 326
 327         if (getenv("TRACE_DEBUG"))
 328                 debug = 1;
 329         unsetenv("TRACE_DEBUG");
 330
 331         child = fork();
 332
 333         if (child == 0) {
 334                 char **_argv = calloc(argc + 1, sizeof(char *));
 335                 char **_envp;
 336                 char *preload = NULL;
 337                 const char *old_preload = getenv("LD_PRELOAD");
 338                 int newenv = 0;
 339                 int envc = 0;
 340                 int ret;
 341
 342                 memcpy(_argv, argv, argc * sizeof(char *));
 343
 344                 while (envp[envc++])
 345                         ;
 346
 347                 _envp = calloc(envc + 2, sizeof(char *));
 348                 switch (mode) {
 349                 case UTRACE:
 350                         preload = "/lib/libpreload-trace.so";
 351                         newenv = 1;
 352                         break;
 353                 case SECCOMP_TRACE:
 354                         preload = "/lib/libpreload-seccomp.so";
 355                         newenv = 2;
 356                         if (asprintf(&_envp[1], "SECCOMP_FILE=%s", json ? json : "") < 0)
 357                                 ULOG_ERR("failed to allocate SECCOMP_FILE env: %m\n");
 358
 359                         kill(getpid(), SIGSTOP);
 360                         break;
 361                 }
 362                 if (asprintf(&_envp[0], "LD_PRELOAD=%s%s%s", preload,
 363                              old_preload ? ":" : "",
 364                               old_preload ? old_preload : "") < 0)
 365                         ULOG_ERR("failed to allocate LD_PRELOAD env: %m\n");
 366
 367                 memcpy(&_envp[newenv], envp, envc * sizeof(char *));
 368
 369                 ret = execve(_argv[0], _argv, _envp);
 370                 ULOG_ERR("failed to exec %s: %m\n", _argv[0]);
 371
 372                 free(_argv);
 373                 free(_envp);
 374                 return ret;
 375         }
 376
 377         if (child < 0)
 378                 return -1;
 379
 380         waitpid(child, &status, WUNTRACED);
 381         if (!WIFSTOPPED(status)) {
 382                 ULOG_ERR("failed to start %s\n", *argv);
 383                 return -1;
 384         }
 385
 386         /* Initialize uloop to catch all ptrace stops from now on. */
 387         uloop_init();
 388
 389         int ptrace_options = PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK | PTRACE_O_TRACECLONE;
 390         switch (mode) {
 391         case UTRACE:
 392                 ptrace_options |= PTRACE_O_TRACESYSGOOD;
 393                 ptrace_restart = PTRACE_SYSCALL;
 394                 break;
 395         case SECCOMP_TRACE:
 396                 ptrace_options |= PTRACE_O_TRACESECCOMP;
 397                 ptrace_restart = PTRACE_CONT;
 398                 break;
 399         }
 400         if (ptrace(PTRACE_SEIZE, child, 0, ptrace_options) == -1) {
 401                 ULOG_ERR("PTRACE_SEIZE: %m\n");
 402                 return -1;
 403         }
 404         if (ptrace(ptrace_restart, child, 0, SIGCONT) == -1) {
 405                 ULOG_ERR("ptrace_restart: %m\n");
 406                 return -1;
 407         }
 408
 409         tracer.proc.pid = child;
 410         tracer.proc.cb = tracer_cb;
 411         uloop_process_add(&tracer.proc);
 412         signal(SIGTERM, sigterm_handler); /* Override uloop's SIGTERM handler */
 413         uloop_run();
 414         uloop_done();
 415
 416
 417         switch (mode) {
 418         case UTRACE:
 419                 if (!json)
 420                         if (asprintf(&json, "/tmp/%s.%u.json", basename(*argv), child) < 0)
 421                                 ULOG_ERR("failed to allocate output path: %m\n");
 422                 break;
 423         case SECCOMP_TRACE:
 424                 if (!violation_count)
 425                         return 0;
 426                 if (asprintf(&json, "/tmp/%s.%u.violations.json", basename(*argv), child) < 0)
 427                         ULOG_ERR("failed to allocate violations output path: %m\n");
 428                 break;
 429         }
 430         print_syscalls(policy, json);
 431         return 0;
 432 }