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
 121         if (mode == UTRACE) {
 122                 set_syscall("rt_sigaction", 1);
 123                 set_syscall("sigreturn", 1);
 124                 set_syscall("rt_sigreturn", 1);
 125                 set_syscall("exit_group", 1);
 126                 set_syscall("exit", 1);
 127         }
 128
 129         struct syscall sorted[SYSCALL_COUNT];
 130
 131         for (i = 0; i < SYSCALL_COUNT; i++) {
 132                 sorted[i].syscall = syscall_index_to_number(i);
 133                 sorted[i].count = syscall_count[i];
 134         }
 135
 136         qsort(sorted, SYSCALL_COUNT, sizeof(sorted[0]), cmp_count);
 137
 138         blob_buf_init(&b, 0);
 139         blobmsg_add_string(&b, "defaultAction", "SCMP_ACT_KILL_PROCESS");
 140         c = blobmsg_open_array(&b, "syscalls");
 141         d = blobmsg_open_table(&b, "");
 142         e = blobmsg_open_array(&b, "names");
 143
 144         for (i = 0; i < SYSCALL_COUNT; i++) {
 145                 int sc = sorted[i].syscall;
 146                 if (!sorted[i].count)
 147                         break;
 148                 if (syscall_name(sc)) {
 149                         if (debug)
 150                                 printf("syscall %d (%s) was called %d times\n",
 151                                        sc, syscall_name(sc), sorted[i].count);
 152                         blobmsg_add_string(&b, NULL, syscall_name(sc));
 153                 } else {
 154                         ULOG_ERR("no name found for syscall(%d)\n", sc);
 155                 }
 156         }
 157         blobmsg_close_array(&b, e);
 158         blobmsg_add_string(&b, "action", "SCMP_ACT_ALLOW");
 159         blobmsg_close_table(&b, d);
 160         blobmsg_close_array(&b, c);
 161         if (json) {
 162                 FILE *fp = fopen(json, "w");
 163                 if (fp) {
 164                         fprintf(fp, "%s\n", blobmsg_format_json_indent(b.head, true, 0));
 165                         fclose(fp);
 166                         ULOG_INFO("saving syscall trace to %s\n", json);
 167                 } else {
 168                         ULOG_ERR("failed to open %s\n", json);
 169                 }
 170         } else {
 171                 printf("%s\n",
 172                         blobmsg_format_json_indent(b.head, true, 0));
 173         }
 174
 175 }
 176
 177 static void report_seccomp_vialation(pid_t pid, unsigned syscall)
 178 {
 179         char buf[200];
 180         snprintf(buf, sizeof(buf), "/proc/%d/cmdline", pid);
 181         int f = open(buf, O_RDONLY);
 182         int r = read(f, buf, sizeof(buf) - 1);
 183         if (r >= 0)
 184                 buf[r] = 0;
 185         else
 186                 strcpy(buf, "unknown?");
 187         close(f);
 188
 189         if (violation_count < INT_MAX)
 190                 violation_count++;
 191         int i = syscall_index(syscall);
 192         if (i >= 0) {
 193                 syscall_count[i]++;
 194                 ULOG_ERR("%s[%u] tried to call non-whitelisted syscall: %s (see %s)\n",
 195                          buf, pid,  syscall_name(syscall), json);
 196         } else {
 197                 ULOG_ERR("%s[%u] tried to call non-whitelisted syscall: %d (see %s)\n",
 198                          buf, pid,  syscall, json);
 199         }
 200 }
 201
 202 static void tracer_cb(struct uloop_process *c, int ret)
 203 {
 204         struct tracee *tracee = container_of(c, struct tracee, proc);
 205         int inject_signal = 0;
 206
 207         /* We explicitely check for events in upper 16 bits, because
 208          * musl (as opposed to glibc) does not report
 209          * PTRACE_EVENT_STOP as WIFSTOPPED */
 210         if (WIFSTOPPED(ret) || (ret >> 16)) {
 211                 if (WSTOPSIG(ret) & 0x80) {
 212                         if (!tracee->in_syscall) {
 213 #ifdef __aarch64__
 214                                 int syscall = -1;
 215                                 struct ptrace_syscall_info ptsi = {.op=PTRACE_SYSCALL_INFO_ENTRY};
 216                                 if (ptrace(PTRACE_GET_SYSCALL_INFO, c->pid, sizeof(ptsi), &ptsi) != -1)
 217                                         syscall = ptsi.entry.nr;
 218 #else
 219                                 int syscall = ptrace(PTRACE_PEEKUSER, c->pid, reg_syscall_nr);
 220 #endif
 221                                 int i = syscall_index(syscall);
 222                                 if (i >= 0) {
 223                                         syscall_count[i]++;
 224                                         if (debug)
 225                                                 fprintf(stderr, "%s()\n", syscall_name(syscall));
 226                                 } else if (debug) {
 227                                         fprintf(stderr, "syscal(%d)\n", syscall);
 228                                 }
 229                         }
 230                         tracee->in_syscall = !tracee->in_syscall;
 231                 } else if ((ret >> 8) == (SIGTRAP | (PTRACE_EVENT_FORK << 8)) ||
 232                            (ret >> 8) == (SIGTRAP | (PTRACE_EVENT_VFORK << 8)) ||
 233                            (ret >> 8) == (SIGTRAP | (PTRACE_EVENT_CLONE << 8))) {
 234                         struct tracee *child = calloc(1, sizeof(struct tracee));
 235
 236                         unsigned long msg;
 237                         ptrace(PTRACE_GETEVENTMSG, c->pid, 0, &msg);
 238                         child->proc.pid = msg;
 239                         child->proc.cb = tracer_cb;
 240                         ptrace(ptrace_restart, child->proc.pid, 0, 0);
 241                         uloop_process_add(&child->proc);
 242                         if (debug)
 243                                 fprintf(stderr, "Tracing new child %d\n", child->proc.pid);
 244                 } else if ((ret >> 16) == PTRACE_EVENT_STOP) {
 245                         /* Nothing special to do here */
 246                 } else if ((ret >> 8) == (SIGTRAP | (PTRACE_EVENT_SECCOMP << 8))) {
 247                         int syscall = ptrace(PTRACE_PEEKUSER, c->pid, reg_syscall_nr);
 248 #if defined(__arm__)
 249                         ptrace(PTRACE_SET_SYSCALL, c->pid, 0, -1);
 250                         ptrace(PTRACE_POKEUSER, c->pid, reg_retval_nr, -ENOSYS);
 251 #else
 252                         ptrace(PTRACE_POKEUSER, c->pid, reg_syscall_nr, -1);
 253 #endif
 254                         report_seccomp_vialation(c->pid, syscall);
 255                 } else {
 256                         inject_signal = WSTOPSIG(ret);
 257                         if (debug)
 258                                 fprintf(stderr, "Injecting signal %d into pid %d\n",
 259                                         inject_signal, tracee->proc.pid);
 260                 }
 261         } else if (WIFEXITED(ret) || (WIFSIGNALED(ret) && WTERMSIG(ret))) {
 262                 if (tracee == &tracer) {
 263                         uloop_end(); /* Main process exit */
 264                 } else {
 265                         if (debug)
 266                                 fprintf(stderr, "Child %d exited\n", tracee->proc.pid);
 267                         free(tracee);
 268                 }
 269                 return;
 270         }
 271
 272         ptrace(ptrace_restart, c->pid, 0, inject_signal);
 273         uloop_process_add(c);
 274 }
 275
 276 static void sigterm_handler(int signum)
 277 {
 278         /* When we receive SIGTERM, we forward it to the tracee. After
 279          * the tracee exits, trace_cb() will be called and make us
 280          * exit too. */
 281         kill(tracer.proc.pid, SIGTERM);
 282 }
 283
 284
 285 int main(int argc, char **argv, char **envp)
 286 {
 287         int status, ch, policy = EPERM;
 288         pid_t child;
 289
 290         /* When invoked via seccomp-trace symlink, work as seccomp
 291          * violation logger rather than as syscall tracer */
 292         if (strstr(argv[0], "seccomp-trace"))
 293                 mode = SECCOMP_TRACE;
 294
 295         while ((ch = getopt(argc, argv, "f:p:")) != -1) {
 296                 switch (ch) {
 297                 case 'f':
 298                         json = optarg;
 299                         break;
 300                 case 'p':
 301                         policy = atoi(optarg);
 302                         break;
 303                 }
 304         }
 305
 306         if (!json)
 307                 json = getenv("SECCOMP_FILE");
 308
 309         argc -= optind;
 310         argv += optind;
 311
 312         if (!argc)
 313                 return -1;
 314
 315         if (getenv("TRACE_DEBUG"))
 316                 debug = 1;
 317         unsetenv("TRACE_DEBUG");
 318
 319         child = fork();
 320
 321         if (child == 0) {
 322                 char **_argv = calloc(argc + 1, sizeof(char *));
 323                 char **_envp;
 324                 char *preload = NULL;
 325                 const char *old_preload = getenv("LD_PRELOAD");
 326                 int newenv = 0;
 327                 int envc = 0;
 328                 int ret;
 329
 330                 memcpy(_argv, argv, argc * sizeof(char *));
 331
 332                 while (envp[envc++])
 333                         ;
 334
 335                 _envp = calloc(envc + 2, sizeof(char *));
 336                 switch (mode) {
 337                 case UTRACE:
 338                         preload = "/lib/libpreload-trace.so";
 339                         newenv = 1;
 340                         break;
 341                 case SECCOMP_TRACE:
 342                         preload = "/lib/libpreload-seccomp.so";
 343                         newenv = 2;
 344                         if (asprintf(&_envp[1], "SECCOMP_FILE=%s", json ? json : "") < 0)
 345                                 ULOG_ERR("failed to allocate SECCOMP_FILE env: %m\n");
 346
 347                         kill(getpid(), SIGSTOP);
 348                         break;
 349                 }
 350                 if (asprintf(&_envp[0], "LD_PRELOAD=%s%s%s", preload,
 351                              old_preload ? ":" : "",
 352                               old_preload ? old_preload : "") < 0)
 353                         ULOG_ERR("failed to allocate LD_PRELOAD env: %m\n");
 354
 355                 memcpy(&_envp[newenv], envp, envc * sizeof(char *));
 356
 357                 ret = execve(_argv[0], _argv, _envp);
 358                 ULOG_ERR("failed to exec %s: %m\n", _argv[0]);
 359
 360                 free(_argv);
 361                 free(_envp);
 362                 return ret;
 363         }
 364
 365         if (child < 0)
 366                 return -1;
 367
 368         waitpid(child, &status, WUNTRACED);
 369         if (!WIFSTOPPED(status)) {
 370                 ULOG_ERR("failed to start %s\n", *argv);
 371                 return -1;
 372         }
 373
 374         /* Initialize uloop to catch all ptrace stops from now on. */
 375         uloop_init();
 376
 377         int ptrace_options = PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK | PTRACE_O_TRACECLONE;
 378         switch (mode) {
 379         case UTRACE:
 380                 ptrace_options |= PTRACE_O_TRACESYSGOOD;
 381                 ptrace_restart = PTRACE_SYSCALL;
 382                 break;
 383         case SECCOMP_TRACE:
 384                 ptrace_options |= PTRACE_O_TRACESECCOMP;
 385                 ptrace_restart = PTRACE_CONT;
 386                 break;
 387         }
 388         if (ptrace(PTRACE_SEIZE, child, 0, ptrace_options) == -1) {
 389                 ULOG_ERR("PTRACE_SEIZE: %m\n");
 390                 return -1;
 391         }
 392         if (ptrace(ptrace_restart, child, 0, SIGCONT) == -1) {
 393                 ULOG_ERR("ptrace_restart: %m\n");
 394                 return -1;
 395         }
 396
 397         tracer.proc.pid = child;
 398         tracer.proc.cb = tracer_cb;
 399         uloop_process_add(&tracer.proc);
 400         signal(SIGTERM, sigterm_handler); /* Override uloop's SIGTERM handler */
 401         uloop_run();
 402         uloop_done();
 403
 404
 405         switch (mode) {
 406         case UTRACE:
 407                 if (!json)
 408                         if (asprintf(&json, "/tmp/%s.%u.json", basename(*argv), child) < 0)
 409                                 ULOG_ERR("failed to allocate output path: %m\n");
 410                 break;
 411         case SECCOMP_TRACE:
 412                 if (!violation_count)
 413                         return 0;
 414                 if (asprintf(&json, "/tmp/%s.%u.violations.json", basename(*argv), child) < 0)
 415                         ULOG_ERR("failed to allocate violations output path: %m\n");
 416                 break;
 417         }
 418         print_syscalls(policy, json);
 419         return 0;
 420 }