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
  29 #ifndef PTRACE_EVENT_STOP
  30 /* PTRACE_EVENT_STOP is defined in linux/ptrace.h, but this header
  31  * collides with musl's sys/ptrace.h */
  32 #define PTRACE_EVENT_STOP 128
  33 #endif
  34
  35 #include <libubox/ulog.h>
  36 #include <libubox/uloop.h>
  37 #include <libubox/blobmsg.h>
  38 #include <libubox/blobmsg_json.h>
  39
  40 #include "../syscall-names.h"
  41
  42 #define _offsetof(a, b) __builtin_offsetof(a,b)
  43 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
  44
  45 #ifdef __amd64__
  46 #define reg_syscall_nr  _offsetof(struct user, regs.orig_rax)
  47 #elif defined(__i386__)
  48 #define reg_syscall_nr  _offsetof(struct user, regs.orig_eax)
  49 #elif defined(__mips)
  50 # ifndef EF_REG2
  51 # define EF_REG2        8
  52 # endif
  53 #define reg_syscall_nr  (EF_REG2 / 4)
  54 #elif defined(__arm__)
  55 #include <asm/ptrace.h>         /* for PTRACE_SET_SYSCALL */
  56 #define reg_syscall_nr  _offsetof(struct user, regs.uregs[7])
  57 # if defined(__ARM_EABI__)
  58 # define reg_retval_nr  _offsetof(struct user, regs.uregs[0])
  59 # endif
  60 #else
  61 #error tracing is not supported on this architecture
  62 #endif
  63
  64 enum mode {
  65         UTRACE,
  66         SECCOMP_TRACE,
  67 } mode = UTRACE;
  68
  69 struct tracee {
  70         struct uloop_process proc;
  71         int in_syscall;
  72 };
  73
  74 static struct tracee tracer;
  75 static int syscall_count[SYSCALL_COUNT];
  76 static int violation_count;
  77 static struct blob_buf b;
  78 static int debug;
  79 char *json = NULL;
  80 int ptrace_restart;
  81
  82 static void set_syscall(const char *name, int val)
  83 {
  84         int i;
  85
  86         for (i = 0; i < SYSCALL_COUNT; i++) {
  87                 int sc = syscall_index_to_number(i);
  88                 if (syscall_name(sc) && !strcmp(syscall_name(sc), name)) {
  89                         syscall_count[i] = val;
  90                         return;
  91                 }
  92         }
  93 }
  94
  95 struct syscall {
  96         int syscall;
  97         int count;
  98 };
  99
 100 static int cmp_count(const void *a, const void *b)
 101 {
 102         return ((struct syscall*)b)->count - ((struct syscall*)a)->count;
 103 }
 104
 105 static void print_syscalls(int policy, const char *json)
 106 {
 107         void *c;
 108         int i;
 109
 110         if (mode == UTRACE) {
 111                 set_syscall("rt_sigaction", 1);
 112                 set_syscall("sigreturn", 1);
 113                 set_syscall("rt_sigreturn", 1);
 114                 set_syscall("exit_group", 1);
 115                 set_syscall("exit", 1);
 116         }
 117
 118         struct syscall sorted[SYSCALL_COUNT];
 119
 120         for (i = 0; i < SYSCALL_COUNT; i++) {
 121                 sorted[i].syscall = syscall_index_to_number(i);
 122                 sorted[i].count = syscall_count[i];
 123         }
 124
 125         qsort(sorted, SYSCALL_COUNT, sizeof(sorted[0]), cmp_count);
 126
 127         blob_buf_init(&b, 0);
 128         c = blobmsg_open_array(&b, "whitelist");
 129
 130         for (i = 0; i < SYSCALL_COUNT; i++) {
 131                 int sc = sorted[i].syscall;
 132                 if (!sorted[i].count)
 133                         break;
 134                 if (syscall_name(sc)) {
 135                         if (debug)
 136                                 printf("syscall %d (%s) was called %d times\n",
 137                                        sc, syscall_name(sc), sorted[i].count);
 138                         blobmsg_add_string(&b, NULL, syscall_name(sc));
 139                 } else {
 140                         ULOG_ERR("no name found for syscall(%d)\n", sc);
 141                 }
 142         }
 143         blobmsg_close_array(&b, c);
 144         blobmsg_add_u32(&b, "policy", policy);
 145         if (json) {
 146                 FILE *fp = fopen(json, "w");
 147                 if (fp) {
 148                         fprintf(fp, "%s", blobmsg_format_json_indent(b.head, true, 0));
 149                         fclose(fp);
 150                         ULOG_INFO("saving syscall trace to %s\n", json);
 151                 } else {
 152                         ULOG_ERR("failed to open %s\n", json);
 153                 }
 154         } else {
 155                 printf("%s\n",
 156                         blobmsg_format_json_indent(b.head, true, 0));
 157         }
 158
 159 }
 160
 161 static void report_seccomp_vialation(pid_t pid, unsigned syscall)
 162 {
 163         char buf[200];
 164         snprintf(buf, sizeof(buf), "/proc/%d/cmdline", pid);
 165         int f = open(buf, O_RDONLY);
 166         int r = read(f, buf, sizeof(buf) - 1);
 167         if (r >= 0)
 168                 buf[r] = 0;
 169         else
 170                 strcpy(buf, "unknown?");
 171         close(f);
 172
 173         if (violation_count < INT_MAX)
 174                 violation_count++;
 175         int i = syscall_index(syscall);
 176         if (i >= 0) {
 177                 syscall_count[i]++;
 178                 ULOG_ERR("%s[%u] tried to call non-whitelisted syscall: %s (see %s)\n",
 179                          buf, pid,  syscall_name(syscall), json);
 180         } else {
 181                 ULOG_ERR("%s[%u] tried to call non-whitelisted syscall: %d (see %s)\n",
 182                          buf, pid,  syscall, json);
 183         }
 184 }
 185
 186 static void tracer_cb(struct uloop_process *c, int ret)
 187 {
 188         struct tracee *tracee = container_of(c, struct tracee, proc);
 189         int inject_signal = 0;
 190
 191         /* We explicitely check for events in upper 16 bits, because
 192          * musl (as opposed to glibc) does not report
 193          * PTRACE_EVENT_STOP as WIFSTOPPED */
 194         if (WIFSTOPPED(ret) || (ret >> 16)) {
 195                 if (WSTOPSIG(ret) & 0x80) {
 196                         if (!tracee->in_syscall) {
 197                                 int syscall = ptrace(PTRACE_PEEKUSER, c->pid, reg_syscall_nr);
 198                                 int i = syscall_index(syscall);
 199                                 if (i >= 0) {
 200                                         syscall_count[i]++;
 201                                         if (debug)
 202                                                 fprintf(stderr, "%s()\n", syscall_name(syscall));
 203                                 } else if (debug) {
 204                                         fprintf(stderr, "syscal(%d)\n", syscall);
 205                                 }
 206                         }
 207                         tracee->in_syscall = !tracee->in_syscall;
 208                 } else if ((ret >> 8) == (SIGTRAP | (PTRACE_EVENT_FORK << 8)) ||
 209                            (ret >> 8) == (SIGTRAP | (PTRACE_EVENT_VFORK << 8)) ||
 210                            (ret >> 8) == (SIGTRAP | (PTRACE_EVENT_CLONE << 8))) {
 211                         struct tracee *child = calloc(1, sizeof(struct tracee));
 212
 213                         ptrace(PTRACE_GETEVENTMSG, c->pid, 0, &child->proc.pid);
 214                         child->proc.cb = tracer_cb;
 215                         ptrace(ptrace_restart, child->proc.pid, 0, 0);
 216                         uloop_process_add(&child->proc);
 217                         if (debug)
 218                                 fprintf(stderr, "Tracing new child %d\n", child->proc.pid);
 219                 } else if ((ret >> 16) == PTRACE_EVENT_STOP) {
 220                         /* Nothing special to do here */
 221                 } else if ((ret >> 8) == (SIGTRAP | (PTRACE_EVENT_SECCOMP << 8))) {
 222                         int syscall = ptrace(PTRACE_PEEKUSER, c->pid, reg_syscall_nr);
 223 #if defined(__arm__)
 224                         ptrace(PTRACE_SET_SYSCALL, c->pid, 0, -1);
 225                         ptrace(PTRACE_POKEUSER, c->pid, reg_retval_nr, -ENOSYS);
 226 #else
 227                         ptrace(PTRACE_POKEUSER, c->pid, reg_syscall_nr, -1);
 228 #endif
 229                         report_seccomp_vialation(c->pid, syscall);
 230                 } else {
 231                         inject_signal = WSTOPSIG(ret);
 232                         if (debug)
 233                                 fprintf(stderr, "Injecting signal %d into pid %d\n",
 234                                         inject_signal, tracee->proc.pid);
 235                 }
 236         } else if (WIFEXITED(ret) || (WIFSIGNALED(ret) && WTERMSIG(ret))) {
 237                 if (tracee == &tracer) {
 238                         uloop_end(); /* Main process exit */
 239                 } else {
 240                         if (debug)
 241                                 fprintf(stderr, "Child %d exited\n", tracee->proc.pid);
 242                         free(tracee);
 243                 }
 244                 return;
 245         }
 246
 247         ptrace(ptrace_restart, c->pid, 0, inject_signal);
 248         uloop_process_add(c);
 249 }
 250
 251 static void sigterm_handler(int signum)
 252 {
 253         /* When we receive SIGTERM, we forward it to the tracee. After
 254          * the tracee exits, trace_cb() will be called and make us
 255          * exit too. */
 256         kill(tracer.proc.pid, SIGTERM);
 257 }
 258
 259
 260 int main(int argc, char **argv, char **envp)
 261 {
 262         int status, ch, policy = EPERM;
 263         pid_t child;
 264
 265         /* When invoked via seccomp-trace symlink, work as seccomp
 266          * violation logger rather than as syscall tracer */
 267         if (strstr(argv[0], "seccomp-trace"))
 268                 mode = SECCOMP_TRACE;
 269
 270         while ((ch = getopt(argc, argv, "f:p:")) != -1) {
 271                 switch (ch) {
 272                 case 'f':
 273                         json = optarg;
 274                         break;
 275                 case 'p':
 276                         policy = atoi(optarg);
 277                         break;
 278                 }
 279         }
 280
 281         if (!json)
 282                 json = getenv("SECCOMP_FILE");
 283
 284         argc -= optind;
 285         argv += optind;
 286
 287         if (!argc)
 288                 return -1;
 289
 290         if (getenv("TRACE_DEBUG"))
 291                 debug = 1;
 292         unsetenv("TRACE_DEBUG");
 293
 294         child = fork();
 295
 296         if (child == 0) {
 297                 char **_argv = calloc(argc + 1, sizeof(char *));
 298                 char **_envp;
 299                 char *preload = NULL;
 300                 const char *old_preload = getenv("LD_PRELOAD");
 301                 int newenv = 0;
 302                 int envc = 0;
 303                 int ret;
 304
 305                 memcpy(_argv, argv, argc * sizeof(char *));
 306
 307                 while (envp[envc++])
 308                         ;
 309
 310                 _envp = calloc(envc + 2, sizeof(char *));
 311                 switch (mode) {
 312                 case UTRACE:
 313                         preload = "/lib/libpreload-trace.so";
 314                         newenv = 1;
 315                         break;
 316                 case SECCOMP_TRACE:
 317                         preload = "/lib/libpreload-seccomp.so";
 318                         newenv = 2;
 319                         asprintf(&_envp[1], "SECCOMP_FILE=%s", json ? json : "");
 320                         kill(getpid(), SIGSTOP);
 321                         break;
 322                 }
 323                 asprintf(&_envp[0], "LD_PRELOAD=%s%s%s", preload,
 324                          old_preload ? ":" : "",
 325                          old_preload ? old_preload : "");
 326                 memcpy(&_envp[newenv], envp, envc * sizeof(char *));
 327
 328                 ret = execve(_argv[0], _argv, _envp);
 329                 ULOG_ERR("failed to exec %s: %s\n", _argv[0], strerror(errno));
 330
 331                 free(_argv);
 332                 free(_envp);
 333                 return ret;
 334         }
 335
 336         if (child < 0)
 337                 return -1;
 338
 339         waitpid(child, &status, WUNTRACED);
 340         if (!WIFSTOPPED(status)) {
 341                 ULOG_ERR("failed to start %s\n", *argv);
 342                 return -1;
 343         }
 344
 345         /* Initialize uloop to catch all ptrace stops from now on. */
 346         uloop_init();
 347
 348         int ptrace_options = PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK | PTRACE_O_TRACECLONE;
 349         switch (mode) {
 350         case UTRACE:
 351                 ptrace_options |= PTRACE_O_TRACESYSGOOD;
 352                 ptrace_restart = PTRACE_SYSCALL;
 353                 break;
 354         case SECCOMP_TRACE:
 355                 ptrace_options |= PTRACE_O_TRACESECCOMP;
 356                 ptrace_restart = PTRACE_CONT;
 357                 break;
 358         }
 359         if (ptrace(PTRACE_SEIZE, child, 0, ptrace_options) == -1) {
 360                 ULOG_ERR("PTRACE_SEIZE: %s\n", strerror(errno));
 361                 return -1;
 362         }
 363         if (ptrace(ptrace_restart, child, 0, SIGCONT) == -1) {
 364                 ULOG_ERR("ptrace_restart: %s\n", strerror(errno));
 365                 return -1;
 366         }
 367
 368         tracer.proc.pid = child;
 369         tracer.proc.cb = tracer_cb;
 370         uloop_process_add(&tracer.proc);
 371         signal(SIGTERM, sigterm_handler); /* Override uloop's SIGTERM handler */
 372         uloop_run();
 373         uloop_done();
 374
 375
 376         switch (mode) {
 377         case UTRACE:
 378                 if (!json)
 379                         if (asprintf(&json, "/tmp/%s.%u.json", basename(*argv), child) < 0)
 380                                 ULOG_ERR("failed to allocate output path: %s\n", strerror(errno));
 381                 break;
 382         case SECCOMP_TRACE:
 383                 if (!violation_count)
 384                         return 0;
 385                 asprintf(&json, "/tmp/%s.%u.violations.json", basename(*argv), child);
 386                 break;
 387         }
 388         print_syscalls(policy, json);
 389         return 0;
 390 }