1 /* 2 * shell_cmd() takes a shell command after %<character> substitutions. The 3 * command is executed by a /bin/sh child process, with standard input, 4 * standard output and standard error connected to /dev/null. 5 * 6 * Diagnostics are reported through syslog(3). 7 * 8 * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands. 9 */ 10 11 #ifndef lint 12 static char sccsid[] = "@(#) shell_cmd.c 1.5 94/12/28 17:42:44"; 13 #endif 14 15 /* System libraries. */ 16 17 #include <sys/types.h> 18 #include <sys/param.h> 19 #include <sys/wait.h> 20 #include <signal.h> 21 #include <stdio.h> 22 #include <syslog.h> 23 #include <string.h> 24 #include <unistd.h> 25 #include <fcntl.h> 26 27 extern void exit(); 28 29 /* Local stuff. */ 30 31 #include "tcpd.h" 32 33 /* Forward declarations. */ 34 35 static void do_child(char *command); 36 37 /* shell_cmd - execute shell command */ 38 39 void shell_cmd(char *command) 40 { 41 int child_pid; 42 int wait_pid; 43 44 /* 45 * Most of the work is done within the child process, to minimize the 46 * risk of damage to the parent. 47 */ 48 49 switch (child_pid = fork()) { 50 case -1: /* error */ 51 tcpd_warn("cannot fork: %m"); 52 break; 53 case 00: /* child */ 54 do_child(command); 55 /* NOTREACHED */ 56 default: /* parent */ 57 while ((wait_pid = wait((int *) 0)) != -1 && wait_pid != child_pid) 58 /* void */ ; 59 } 60 } 61 62 /* do_child - exec command with { stdin, stdout, stderr } to /dev/null */ 63 64 static void do_child(char *command) 65 { 66 char *error; 67 int tmp_fd; 68 69 /* 70 * Systems with POSIX sessions may send a SIGHUP to grandchildren if the 71 * child exits first. This is sick, sessions were invented for terminals. 72 */ 73 74 signal(SIGHUP, SIG_IGN); 75 76 /* Set up new stdin, stdout, stderr, and exec the shell command. */ 77 78 for (tmp_fd = 0; tmp_fd < 3; tmp_fd++) 79 (void) close(tmp_fd); 80 if (open("/dev/null", 2) != 0) { 81 error = "open /dev/null: %m"; 82 } else if (dup(0) != 1 || dup(0) != 2) { 83 error = "dup: %m"; 84 } else { 85 (void) execl("/bin/sh", "sh", "-c", command, (char *) 0); 86 error = "execl /bin/sh: %m"; 87 } 88 89 /* Something went wrong. We MUST terminate the child process. */ 90 91 tcpd_warn(error); 92 _exit(0); 93 } 94