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 <err.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 #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 #define PROC_NAME(mode) (mode == UTRACE ? "utrace" : "seccomp-trace")
  70
  71 #define INFO(fmt, ...) do { \
  72         fprintf(stderr, "%s: "fmt, PROC_NAME(mode), ## __VA_ARGS__); \
  73 } while (0)
  74
  75 #define ERROR(fmt, ...) do { \
  76         syslog(LOG_ERR, "%s: "fmt, PROC_NAME(mode), ## __VA_ARGS__); \
  77         fprintf(stderr, "%s: "fmt, PROC_NAME(mode), ## __VA_ARGS__);  \
  78 } while (0)
  79
  80 #define LOGERR(fmt, ...) do { \
  81         syslog(LOG_ERR, "%s: "fmt, PROC_NAME(mode), ## __VA_ARGS__); \
  82 } while (0)
  83
  84 struct tracee {
  85         struct uloop_process proc;
  86         int in_syscall;
  87 };
  88
  89 static struct tracee tracer;
  90 static int *syscall_count;
  91 static int violation_count;
  92 static struct blob_buf b;
  93 static int syscall_max;
  94 static int debug;
  95 char *json = NULL;
  96 int ptrace_restart;
  97
  98 static int max_syscall = ARRAY_SIZE(syscall_names);
  99
 100 static void set_syscall(const char *name, int val)
 101 {
 102         int i;
 103
 104         for (i = 0; i < max_syscall; i++)
 105                 if (syscall_names[i] && !strcmp(syscall_names[i], name)) {
 106                         syscall_count[i] = val;
 107                         return;
 108                 }
 109 }
 110
 111 struct syscall {
 112         int syscall;
 113         int count;
 114 };
 115
 116 static int cmp_count(const void *a, const void *b)
 117 {
 118         return ((struct syscall*)b)->count - ((struct syscall*)a)->count;
 119 }
 120
 121 static void print_syscalls(int policy, const char *json)
 122 {
 123         void *c;
 124         int i;
 125
 126         if (mode == UTRACE) {
 127                 set_syscall("rt_sigaction", 1);
 128                 set_syscall("sigreturn", 1);
 129                 set_syscall("rt_sigreturn", 1);
 130                 set_syscall("exit_group", 1);
 131                 set_syscall("exit", 1);
 132         }
 133
 134         struct syscall sorted[ARRAY_SIZE(syscall_names)];
 135
 136         for (i = 0; i < ARRAY_SIZE(syscall_names); i++) {
 137                 sorted[i].syscall = i;
 138                 sorted[i].count = syscall_count[i];
 139         }
 140
 141         qsort(sorted, ARRAY_SIZE(syscall_names), sizeof(sorted[0]), cmp_count);
 142
 143         blob_buf_init(&b, 0);
 144         c = blobmsg_open_array(&b, "whitelist");
 145
 146         for (i = 0; i < ARRAY_SIZE(syscall_names); i++) {
 147                 int sc = sorted[i].syscall;
 148                 if (!sorted[i].count)
 149                         break;
 150                 if (syscall_names[sc]) {
 151                         if (debug)
 152                                 printf("syscall %d (%s) was called %d times\n",
 153                                         sc, syscall_names[sc], sorted[i].count);
 154                         blobmsg_add_string(&b, NULL, syscall_names[sc]);
 155                 } else {
 156                         ERROR("no name found for syscall(%d)\n", sc);
 157                 }
 158         }
 159         blobmsg_close_array(&b, c);
 160         blobmsg_add_u32(&b, "policy", policy);
 161         if (json) {
 162                 FILE *fp = fopen(json, "w");
 163                 if (fp) {
 164                         fprintf(fp, "%s", blobmsg_format_json_indent(b.head, true, 0));
 165                         fclose(fp);
 166                         INFO("saving syscall trace to %s\n", json);
 167                 } else {
 168                         ERROR("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         if (syscall < ARRAY_SIZE(syscall_names)) {
 192                 syscall_count[syscall]++;
 193                 LOGERR("%s[%u] tried to call non-whitelisted syscall: %s (see %s)\n",
 194                        buf, pid,  syscall_names[syscall], json);
 195         } else {
 196                 LOGERR("%s[%u] tried to call non-whitelisted syscall: %d (see %s)\n",
 197                        buf, pid,  syscall, json);
 198         }
 199 }
 200
 201 static void tracer_cb(struct uloop_process *c, int ret)
 202 {
 203         struct tracee *tracee = container_of(c, struct tracee, proc);
 204         int inject_signal = 0;
 205
 206         /* We explicitely check for events in upper 16 bits, because
 207          * musl (as opposed to glibc) does not report
 208          * PTRACE_EVENT_STOP as WIFSTOPPED */
 209         if (WIFSTOPPED(ret) || (ret >> 16)) {
 210                 if (WSTOPSIG(ret) & 0x80) {
 211                         if (!tracee->in_syscall) {
 212                                 int syscall = ptrace(PTRACE_PEEKUSER, c->pid, reg_syscall_nr);
 213
 214                                 if (syscall < syscall_max) {
 215                                         syscall_count[syscall]++;
 216                                         if (debug)
 217                                                 fprintf(stderr, "%s()\n", syscall_names[syscall]);
 218                                 } else if (debug) {
 219                                         fprintf(stderr, "syscal(%d)\n", syscall);
 220                                 }
 221                         }
 222                         tracee->in_syscall = !tracee->in_syscall;
 223                 } else if ((ret >> 8) == (SIGTRAP | (PTRACE_EVENT_FORK << 8)) ||
 224                            (ret >> 8) == (SIGTRAP | (PTRACE_EVENT_VFORK << 8)) ||
 225                            (ret >> 8) == (SIGTRAP | (PTRACE_EVENT_CLONE << 8))) {
 226                         struct tracee *child = calloc(1, sizeof(struct tracee));
 227
 228                         ptrace(PTRACE_GETEVENTMSG, c->pid, 0, &child->proc.pid);
 229                         child->proc.cb = tracer_cb;
 230                         ptrace(ptrace_restart, child->proc.pid, 0, 0);
 231                         uloop_process_add(&child->proc);
 232                         if (debug)
 233                                 fprintf(stderr, "Tracing new child %d\n", child->proc.pid);
 234                 } else if ((ret >> 16) == PTRACE_EVENT_STOP) {
 235                         /* Nothing special to do here */
 236                 } else if ((ret >> 8) == (SIGTRAP | (PTRACE_EVENT_SECCOMP << 8))) {
 237                         int syscall = ptrace(PTRACE_PEEKUSER, c->pid, reg_syscall_nr);
 238 #if defined(__arm__)
 239                         ptrace(PTRACE_SET_SYSCALL, c->pid, 0, -1);
 240                         ptrace(PTRACE_POKEUSER, c->pid, reg_retval_nr, -ENOSYS);
 241 #else
 242                         ptrace(PTRACE_POKEUSER, c->pid, reg_syscall_nr, -1);
 243 #endif
 244                         report_seccomp_vialation(c->pid, syscall);
 245                 } else {
 246                         inject_signal = WSTOPSIG(ret);
 247                         if (debug)
 248                                 fprintf(stderr, "Injecting signal %d into pid %d\n",
 249                                         inject_signal, tracee->proc.pid);
 250                 }
 251         } else if (WIFEXITED(ret) || (WIFSIGNALED(ret) && WTERMSIG(ret))) {
 252                 if (tracee == &tracer) {
 253                         uloop_end(); /* Main process exit */
 254                 } else {
 255                         if (debug)
 256                                 fprintf(stderr, "Child %d exited\n", tracee->proc.pid);
 257                         free(tracee);
 258                 }
 259                 return;
 260         }
 261
 262         ptrace(ptrace_restart, c->pid, 0, inject_signal);
 263         uloop_process_add(c);
 264 }
 265
 266 static void sigterm_handler(int signum)
 267 {
 268         /* When we receive SIGTERM, we forward it to the tracee. After
 269          * the tracee exits, trace_cb() will be called and make us
 270          * exit too. */
 271         kill(tracer.proc.pid, SIGTERM);
 272 }
 273
 274
 275 int main(int argc, char **argv, char **envp)
 276 {
 277         int status, ch, policy = EPERM;
 278         pid_t child;
 279
 280         /* When invoked via seccomp-trace symlink, work as seccomp
 281          * violation logger rather than as syscall tracer */
 282         if (strstr(argv[0], "seccomp-trace"))
 283                 mode = SECCOMP_TRACE;
 284
 285         while ((ch = getopt(argc, argv, "f:p:")) != -1) {
 286                 switch (ch) {
 287                 case 'f':
 288                         json = optarg;
 289                         break;
 290                 case 'p':
 291                         policy = atoi(optarg);
 292                         break;
 293                 }
 294         }
 295
 296         if (!json)
 297                 json = getenv("SECCOMP_FILE");
 298
 299         argc -= optind;
 300         argv += optind;
 301
 302         if (!argc)
 303                 return -1;
 304
 305         if (getenv("TRACE_DEBUG"))
 306                 debug = 1;
 307         unsetenv("TRACE_DEBUG");
 308
 309         child = fork();
 310
 311         if (child == 0) {
 312                 char **_argv = calloc(argc + 1, sizeof(char *));
 313                 char **_envp;
 314                 char *preload = NULL;
 315                 const char *old_preload = getenv("LD_PRELOAD");
 316                 int newenv = 0;
 317                 int envc = 0;
 318                 int ret;
 319
 320                 memcpy(_argv, argv, argc * sizeof(char *));
 321
 322                 while (envp[envc++])
 323                         ;
 324
 325                 _envp = calloc(envc + 2, sizeof(char *));
 326                 switch (mode) {
 327                 case UTRACE:
 328                         preload = "/lib/libpreload-trace.so";
 329                         newenv = 1;
 330                         break;
 331                 case SECCOMP_TRACE:
 332                         preload = "/lib/libpreload-seccomp.so";
 333                         newenv = 2;
 334                         asprintf(&_envp[1], "SECCOMP_FILE=%s", json ? json : "");
 335                         kill(getpid(), SIGSTOP);
 336                         break;
 337                 }
 338                 asprintf(&_envp[0], "LD_PRELOAD=%s%s%s", preload,
 339                          old_preload ? ":" : "",
 340                          old_preload ? old_preload : "");
 341                 memcpy(&_envp[newenv], envp, envc * sizeof(char *));
 342
 343                 ret = execve(_argv[0], _argv, _envp);
 344                 ERROR("failed to exec %s: %s\n", _argv[0], strerror(errno));
 345
 346                 free(_argv);
 347                 free(_envp);
 348                 return ret;
 349         }
 350
 351         if (child < 0)
 352                 return -1;
 353
 354         syscall_max = ARRAY_SIZE(syscall_names);
 355         syscall_count = calloc(syscall_max, sizeof(int));
 356         waitpid(child, &status, WUNTRACED);
 357         if (!WIFSTOPPED(status)) {
 358                 ERROR("failed to start %s\n", *argv);
 359                 return -1;
 360         }
 361
 362         int ptrace_options = PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK | PTRACE_O_TRACECLONE;
 363         switch (mode) {
 364         case UTRACE:
 365                 ptrace_options |= PTRACE_O_TRACESYSGOOD;
 366                 ptrace_restart = PTRACE_SYSCALL;
 367                 break;
 368         case SECCOMP_TRACE:
 369                 ptrace_options |= PTRACE_O_TRACESECCOMP;
 370                 ptrace_restart = PTRACE_CONT;
 371                 break;
 372         }
 373         if (ptrace(PTRACE_SEIZE, child, 0, ptrace_options) == -1)
 374                 err(1, "PTRACE_SEIZE");
 375         if (ptrace(ptrace_restart, child, 0, SIGCONT) == -1)
 376                 err(1, "ptrace restart");
 377
 378         uloop_init();
 379         tracer.proc.pid = child;
 380         tracer.proc.cb = tracer_cb;
 381         uloop_process_add(&tracer.proc);
 382         signal(SIGTERM, sigterm_handler); /* Override uloop's SIGTERM handler */
 383         uloop_run();
 384         uloop_done();
 385
 386
 387         switch (mode) {
 388         case UTRACE:
 389                 if (!json)
 390                         if (asprintf(&json, "/tmp/%s.%u.json", basename(*argv), child) < 0)
 391                                 ERROR("failed to allocate output path: %s\n", strerror(errno));
 392                 break;
 393         case SECCOMP_TRACE:
 394                 if (!violation_count)
 395                         return 0;
 396                 asprintf(&json, "/tmp/%s.%u.violations.json", basename(*argv), child);
 397                 break;
 398         }
 399         print_syscalls(policy, json);
 400         return 0;
 401 }