Here is an updated version taking care of /tmp file creation races. Thanks to Frank Ch. Eigler for pointing this out.
A small note: pending a large change in LTTng that will allow arming tracepoints on a per-session basis, the current version of the script cannot be run in multiple instances concurrently (interaction between the multiple ltt-armall/ltt-disarmall). I'm also thinking to use mktemp for the next version to create a temporary file rather than the hardcoded file I'm using now. I could save the information about the last file name used in the user's home directory. Thanks, Mathieu /* * lttngtrace.c * * lttngtrace starts/stop system wide tracing around program execution. * * Copyright (c) 2010 Mathieu Desnoyers <[email protected]> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License along * with this program; if not, write to the Free Software Foundation, Inc., * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. * * This file should be setuid root, and belong to a "tracing" group. Only users * part of the tracing group can trace and view the traces gathered. */ #include <errno.h> #include <stdio.h> #include <fcntl.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <limits.h> #include <dirent.h> #include <sys/wait.h> #include <sys/stat.h> #include <sys/types.h> #if DEBUG #define printf_dbg(fmt, args...) printf(fmt, args) #else #define printf_dbg(fmt, ...) #endif int recunlink(const char *dirname) { DIR *dir; struct dirent *entry; char path[PATH_MAX]; dir = opendir(dirname); if (dir == NULL) { if (errno == ENOENT) return 0; perror("Error opendir()"); return -errno; } while ((entry = readdir(dir)) != NULL) { if (strcmp(entry->d_name, ".") && strcmp(entry->d_name, "..")) { snprintf(path, (size_t) PATH_MAX, "%s/%s", dirname, entry->d_name); if (entry->d_type == DT_DIR) recunlink(path); else unlink(path); } } closedir(dir); rmdir(dirname); return 0; } int start_tracing(void) { int ret; ret = recunlink("/tmp/autotrace1"); if (ret) return ret; ret = unlink("/tmp/autotrace1-pid"); if (ret) return ret; /* * Create the directory in /tmp to deal with races (refuse if fail). * Only allow user and group to read the trace data (to limit * information disclosure). */ ret = mkdir("/tmp/autotrace1", S_IRWXU|S_IRWXG); if (ret) { perror("Trace directory creation race"); return ret; } ret = system("ltt-armall > /dev/null"); if (ret) return ret; ret = system("lttctl -C -w /tmp/autotrace1 autotrace1 > /dev/null"); if (ret) return ret; } int stop_tracing(uid_t uid, gid_t egid) { int ret; ret = system("lttctl -D autotrace1 > /dev/null"); if (ret) return ret; ret = system("ltt-disarmall > /dev/null"); if (ret) return ret; /* Hand the trace back to the user after tracing is over */ printf("uid: %d egid %d\n", uid, egid); ret = chown("/tmp/autotrace1", uid, egid); if (ret) { perror("chown error"); return ret; } } int write_child_pid(pid_t pid, uid_t uid, gid_t gid) { int fd; FILE *fp; int ret; /* Create the file as exclusive to deal with /tmp file creation races */ fd = open("/tmp/autotrace1-pid", O_WRONLY | O_CREAT | O_EXCL | O_TRUNC, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP); fp = fdopen(fd, "w"); if (!fp) { perror("Error writing child pid"); return -errno; } fprintf(fp, "%u", (unsigned int) pid); ret = fclose(fp); if (ret) perror("Error in fclose"); /* Hand pid information file back to user */ ret = chown("/tmp/autotrace1-pid", uid, gid); if (ret) perror("chown error"); return ret; } int main(int argc, char *argv[]) { uid_t euid, uid; gid_t egid, gid; pid_t pid; int gret = 0, ret = 0; if (argc < 2) return -ENOENT; euid = geteuid(); uid = getuid(); egid = getegid(); gid = geteuid(); if (euid != 0) { printf("%s must be setuid root\n", argv[0]); return -EPERM; } printf_dbg("euid: %d\n", euid); printf_dbg("uid: %d\n", uid); printf_dbg("egid: %d\n", egid); printf_dbg("gid: %d\n", gid); ret = start_tracing(); gret = (gret == 0) ? ret : gret; pid = fork(); if (pid > 0) { /* parent */ int status; pid = wait(&status); if (pid == -1) gret = (gret == 0) ? -errno : gret; ret = stop_tracing(uid, egid); gret = (gret == 0) ? ret : gret; ret = write_child_pid(pid, uid, egid); gret = (gret == 0) ? ret : gret; } else if (pid == 0) { /* child */ /* Drop root euid before executing child program */ seteuid(uid); ret = execvp(argv[1], &argv[1]); if (ret) perror("Execution error"); return ret; } else { /* error */ perror("Error in fork"); return -errno; } return ret; } -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com _______________________________________________ ltt-dev mailing list [email protected] http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
