lttng/lttngtrace.c

   1 /*
   2  * lttngtrace.c
   3  *
   4  * lttngtrace starts/stop system wide tracing around program execution.
   5  *
   6  * Copyright (c) 2010 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License along
  19  * with this program; if not, write to the Free Software Foundation, Inc.,
  20  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  21  *
  22  * This file should be setuid root, and belong to a "tracing" group. Only users
  23  * part of the tracing group can trace and view the traces gathered.
  24  *
  25  * TODO: LTTng should support per-session tracepoint activation.
  26  * TODO: use mkstemp() and save last trace name in user's home directory.
  27  * TODO: drop priv + reenable standard signal handlers + call lttv at the end.
  28  */
  29
  30 #include <errno.h>
  31 #include <stdio.h>
  32 #include <fcntl.h>
  33 #include <signal.h>
  34 #include <unistd.h>
  35 #include <stdlib.h>
  36 #include <string.h>
  37 #include <limits.h>
  38 #include <dirent.h>
  39 #include <sys/wait.h>
  40 #include <sys/stat.h>
  41 #include <sys/types.h>
  42
  43 #if DEBUG
  44 #define printf_dbg(fmt, args...)        printf(fmt, args)
  45 #else
  46 #define printf_dbg(fmt, ...)
  47 #endif
  48
  49 static char *trace_path;
  50 static char trace_path_pid[PATH_MAX];
  51 static int autotrace;   /*
  52                          * Is the trace_path automatically chosen in /tmp ? Can
  53                          * we unlink if needed ?
  54                          */
  55 static int sigfwd_pid;
  56
  57 static int recunlink(const char *dirname)
  58 {
  59         DIR *dir;
  60         struct dirent *entry;
  61         char path[PATH_MAX];
  62
  63         dir = opendir(dirname);
  64         if (dir == NULL) {
  65                 if (errno == ENOENT)
  66                         return 0;
  67                 perror("Error opendir()");
  68                 return -errno;
  69         }
  70
  71         while ((entry = readdir(dir)) != NULL) {
  72                 if (strcmp(entry->d_name, ".") && strcmp(entry->d_name, "..")) {
  73                         snprintf(path, (size_t) PATH_MAX, "%s/%s", dirname,
  74                                  entry->d_name);
  75                         if (entry->d_type == DT_DIR)
  76                                 recunlink(path);
  77                         else
  78                                 unlink(path);
  79                 }
  80         }
  81         closedir(dir);
  82         rmdir(dirname);
  83
  84         return 0;
  85 }
  86
  87 static int start_tracing(void)
  88 {
  89         int ret;
  90         char command[PATH_MAX];
  91
  92         if (autotrace) {
  93                 ret = recunlink(trace_path);
  94                 if (ret)
  95                         return ret;
  96         }
  97
  98         /*
  99          * Create the directory in /tmp to deal with races (refuse if fail).
 100          * Only allow user and group to read the trace data (to limit
 101          * information disclosure).
 102          */
 103         ret = mkdir(trace_path, S_IRWXU|S_IRWXG);
 104         if (ret) {
 105                 perror("Trace directory creation error");
 106                 return ret;
 107         }
 108         ret = system("ltt-armall > /dev/null");
 109         if (ret)
 110                 return ret;
 111
 112         ret = snprintf(command, PATH_MAX - 1,
 113                        "lttctl -C -w %s autotrace1 > /dev/null",
 114                        trace_path);
 115         ret = ret < 0 ? ret : 0;
 116         if (ret)
 117                 return ret;
 118         ret = system(command);
 119         if (ret)
 120                 return ret;
 121 }
 122
 123 static int stop_tracing(uid_t uid, gid_t egid)
 124 {
 125         int ret;
 126
 127         ret = system("lttctl -D autotrace1 > /dev/null");
 128         if (ret)
 129                 return ret;
 130         ret = system("ltt-disarmall > /dev/null");
 131         if (ret)
 132                 return ret;
 133         /* Hand the trace back to the user after tracing is over */
 134         ret = chown(trace_path, uid, egid);
 135         if (ret) {
 136                 perror("chown error");
 137                 return ret;
 138         }
 139 }
 140
 141 static int write_child_pid(pid_t pid, uid_t uid, gid_t gid)
 142 {
 143         int fd;
 144         FILE *fp;
 145         int ret;
 146
 147         /* Create the file as exclusive to deal with /tmp file creation races */
 148         fd = open(trace_path_pid, O_WRONLY | O_CREAT | O_EXCL | O_TRUNC,
 149                   S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
 150         fp = fdopen(fd, "w");
 151         if (!fp) {
 152                 perror("Error writing child pid");
 153                 return -errno;
 154         }
 155
 156         fprintf(fp, "%u", (unsigned int) pid);
 157         ret = fclose(fp);
 158         if (ret)
 159                 perror("Error in fclose");
 160         /* Hand pid information file back to user */
 161         ret = chown(trace_path_pid, uid, gid);
 162         if (ret)
 163                 perror("chown error");
 164         return ret;
 165 }
 166
 167 static int parse_options(int argc, char *argv[], int *arg)
 168 {
 169         int ret = 0;
 170
 171         for (;;) {
 172                 if (*arg >= argc
 173                     || argv[*arg][0] != '-'
 174                     || argv[*arg][0] == '\0'
 175                     || argv[*arg][1] == '\0'
 176                     || !strcmp(argv[*arg], "--"))
 177                         break;
 178                 switch (argv[*arg][1]) {
 179                 case 'o':       if (*arg + 1 >= argc) {
 180                                         printf("Missing -o trace name\n");
 181                                         ret = -EINVAL;
 182                                         break;
 183                                 }
 184                                 trace_path = argv[*arg + 1];
 185                                 (*arg) += 2;
 186                                 break;
 187                 default:        printf("Unknown option -%c\n", argv[*arg][1]);
 188                                 ret = -EINVAL;
 189                                 return ret;
 190                 }
 191         }
 192         return ret;
 193 }
 194
 195 static int init_trace_path(void)
 196 {
 197         int ret;
 198
 199         if (!trace_path) {
 200                 trace_path = "/tmp/autotrace1";
 201                 autotrace = 1;
 202         }
 203         ret = snprintf(trace_path_pid, PATH_MAX - 1, "%s/%s",
 204                        trace_path, "pid");
 205         ret = ret < 0 ? ret : 0;
 206         return ret;
 207 }
 208
 209 static void sighandler(int signo, siginfo_t *siginfo, void *context)
 210 {
 211         kill(sigfwd_pid, signo);
 212 }
 213
 214 static int init_sighand(sigset_t *saved_mask)
 215 {
 216         sigset_t sig_all_mask;
 217         int gret = 0, ret;
 218
 219         /* Block signals */
 220         ret = sigfillset(&sig_all_mask);
 221         if (ret)
 222                 perror("Error in sigfillset");
 223         gret = (gret == 0) ? ret : gret;
 224         ret = sigprocmask(SIG_SETMASK, &sig_all_mask, saved_mask);
 225         if (ret)
 226                 perror("Error in sigprocmask");
 227         gret = (gret == 0) ? ret : gret;
 228         return gret;
 229 }
 230
 231 static int forward_signals(pid_t pid, sigset_t *saved_mask)
 232 {
 233         struct sigaction act;
 234         int gret = 0, ret;
 235
 236         /* Forward SIGINT and SIGTERM */
 237         sigfwd_pid = pid;
 238         act.sa_sigaction = sighandler;
 239         act.sa_flags = SA_SIGINFO | SA_RESTART;
 240         sigemptyset(&act.sa_mask);
 241         ret = sigaction(SIGINT, &act, NULL);
 242         if (ret)
 243                 perror("Error in sigaction");
 244         gret = (gret == 0) ? ret : gret;
 245         ret = sigaction(SIGTERM, &act, NULL);
 246         if (ret)
 247                 perror("Error in sigaction");
 248         gret = (gret == 0) ? ret : gret;
 249
 250         /* Reenable signals */
 251         ret = sigprocmask(SIG_SETMASK, saved_mask, NULL);
 252         if (ret)
 253                 perror("Error in sigprocmask");
 254         gret = (gret == 0) ? ret : gret;
 255         return gret;
 256 }
 257
 258 int main(int argc, char *argv[])
 259 {
 260         uid_t euid, uid;
 261         gid_t egid, gid;
 262         pid_t pid;
 263         int gret = 0, ret = 0;
 264         int arg = 1;
 265         sigset_t saved_mask;
 266
 267         if (argc < 2)
 268                 return -ENOENT;
 269
 270         euid = geteuid();
 271         uid = getuid();
 272         egid = getegid();
 273         gid = geteuid();
 274
 275         if (euid != 0 && uid != 0) {
 276                 printf("%s must be setuid root\n", argv[0]);
 277                 return -EPERM;
 278         }
 279
 280         printf_dbg("euid: %d\n", euid);
 281         printf_dbg("uid: %d\n", uid);
 282         printf_dbg("egid: %d\n", egid);
 283         printf_dbg("gid: %d\n", gid);
 284
 285         if (arg < argc) {
 286                 ret = parse_options(argc, argv, &arg);
 287                 if (ret)
 288                         return ret;
 289         }
 290
 291         ret = init_trace_path();
 292         gret = (gret == 0) ? ret : gret;
 293
 294         ret = init_sighand(&saved_mask);
 295         gret = (gret == 0) ? ret : gret;
 296
 297         ret = start_tracing();
 298         if (ret)
 299                 return ret;
 300
 301         pid = fork();
 302         if (pid > 0) {          /* parent */
 303                 int status;
 304
 305                 ret = forward_signals(pid, &saved_mask);
 306                 gret = (gret == 0) ? ret : gret;
 307                 pid = wait(&status);
 308                 if (pid == -1)
 309                         gret = (gret == 0) ? -errno : gret;
 310
 311                 ret = stop_tracing(uid, egid);
 312                 gret = (gret == 0) ? ret : gret;
 313                 ret = write_child_pid(pid, uid, egid);
 314                 gret = (gret == 0) ? ret : gret;
 315         } else if (pid == 0) {  /* child */
 316                 /* Drop root euid before executing child program */
 317                 seteuid(uid);
 318                 /* Reenable signals */
 319                 ret = sigprocmask(SIG_SETMASK, &saved_mask, NULL);
 320                 if (ret) {
 321                         perror("Error in sigprocmask");
 322                         return ret;
 323                 }
 324                 ret = execvp(argv[arg], &argv[arg]);
 325                 if (ret)
 326                         perror("Execution error");
 327                 return ret;
 328         } else {                /* error */
 329                 perror("Error in fork");
 330                 return -errno;
 331         }
 332         return ret;
 333 }