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(command) 40 char *command; 41 { 42 int child_pid; 43 int wait_pid; 44 45 /* 46 * Most of the work is done within the child process, to minimize the 47 * risk of damage to the parent. 48 */ 49 50 switch (child_pid = fork()) { 51 case -1: /* error */ 52 tcpd_warn("cannot fork: %m"); 53 break; 54 case 00: /* child */ 55 do_child(command); 56 /* NOTREACHED */ 57 default: /* parent */ 58 while ((wait_pid = wait((int *) 0)) != -1 && wait_pid != child_pid) 59 /* void */ ; 60 } 61 } 62 63 /* do_child - exec command with { stdin, stdout, stderr } to /dev/null */ 64 65 static void do_child(char *command) 66 { 67 char *error; 68 int tmp_fd; 69 70 /* 71 * Systems with POSIX sessions may send a SIGHUP to grandchildren if the 72 * child exits first. This is sick, sessions were invented for terminals. 73 */ 74 75 signal(SIGHUP, SIG_IGN); 76 77 /* Set up new stdin, stdout, stderr, and exec the shell command. */ 78 79 for (tmp_fd = 0; tmp_fd < 3; tmp_fd++) 80 (void) close(tmp_fd); 81 if (open("/dev/null", 2) != 0) { 82 error = "open /dev/null: %m"; 83 } else if (dup(0) != 1 || dup(0) != 2) { 84 error = "dup: %m"; 85 } else { 86 (void) execl("/bin/sh", "sh", "-c", command, (char *) 0); 87 error = "execl /bin/sh: %m"; 88 } 89 90 /* Something went wrong. We MUST terminate the child process. */ 91 92 tcpd_warn(error); 93 _exit(0); 94 } 95