1*0Sstevel@tonic-gate /*
2*0Sstevel@tonic-gate * safe_finger - finger client wrapper that protects against nasty stuff
3*0Sstevel@tonic-gate * from finger servers. Use this program for automatic reverse finger
4*0Sstevel@tonic-gate * probes, not the raw finger command.
5*0Sstevel@tonic-gate *
6*0Sstevel@tonic-gate * Build with: cc -o safe_finger safe_finger.c
7*0Sstevel@tonic-gate *
8*0Sstevel@tonic-gate * The problem: some programs may react to stuff in the first column. Other
9*0Sstevel@tonic-gate * programs may get upset by thrash anywhere on a line. File systems may
10*0Sstevel@tonic-gate * fill up as the finger server keeps sending data. Text editors may bomb
11*0Sstevel@tonic-gate * out on extremely long lines. The finger server may take forever because
12*0Sstevel@tonic-gate * it is somehow wedged. The code below takes care of all this badness.
13*0Sstevel@tonic-gate *
14*0Sstevel@tonic-gate * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
15*0Sstevel@tonic-gate */
16*0Sstevel@tonic-gate
17*0Sstevel@tonic-gate #ifndef lint
18*0Sstevel@tonic-gate static char sccsid[] = "@(#) safe_finger.c 1.4 94/12/28 17:42:41";
19*0Sstevel@tonic-gate #endif
20*0Sstevel@tonic-gate
21*0Sstevel@tonic-gate /* System libraries */
22*0Sstevel@tonic-gate
23*0Sstevel@tonic-gate #include <sys/types.h>
24*0Sstevel@tonic-gate #include <sys/stat.h>
25*0Sstevel@tonic-gate #include <signal.h>
26*0Sstevel@tonic-gate #include <stdio.h>
27*0Sstevel@tonic-gate #include <ctype.h>
28*0Sstevel@tonic-gate #include <pwd.h>
29*0Sstevel@tonic-gate
30*0Sstevel@tonic-gate extern void exit();
31*0Sstevel@tonic-gate
32*0Sstevel@tonic-gate /* Local stuff */
33*0Sstevel@tonic-gate
34*0Sstevel@tonic-gate char path[] = "PATH=/bin:/usr/bin:/usr/ucb:/usr/bsd:/etc:/usr/etc:/usr/sbin";
35*0Sstevel@tonic-gate
36*0Sstevel@tonic-gate #define TIME_LIMIT 60 /* Do not keep listinging forever */
37*0Sstevel@tonic-gate #define INPUT_LENGTH 100000 /* Do not keep listinging forever */
38*0Sstevel@tonic-gate #define LINE_LENGTH 128 /* Editors can choke on long lines */
39*0Sstevel@tonic-gate #define FINGER_PROGRAM "finger" /* Most, if not all, UNIX systems */
40*0Sstevel@tonic-gate #define UNPRIV_NAME "nobody" /* Preferred privilege level */
41*0Sstevel@tonic-gate #define UNPRIV_UGID 32767 /* Default uid and gid */
42*0Sstevel@tonic-gate
43*0Sstevel@tonic-gate int finger_pid;
44*0Sstevel@tonic-gate
cleanup(sig)45*0Sstevel@tonic-gate void cleanup(sig)
46*0Sstevel@tonic-gate int sig;
47*0Sstevel@tonic-gate {
48*0Sstevel@tonic-gate kill(finger_pid, SIGKILL);
49*0Sstevel@tonic-gate exit(0);
50*0Sstevel@tonic-gate }
51*0Sstevel@tonic-gate
main(argc,argv)52*0Sstevel@tonic-gate main(argc, argv)
53*0Sstevel@tonic-gate int argc;
54*0Sstevel@tonic-gate char **argv;
55*0Sstevel@tonic-gate {
56*0Sstevel@tonic-gate int c;
57*0Sstevel@tonic-gate int line_length = 0;
58*0Sstevel@tonic-gate int finger_status;
59*0Sstevel@tonic-gate int wait_pid;
60*0Sstevel@tonic-gate int input_count = 0;
61*0Sstevel@tonic-gate struct passwd *pwd;
62*0Sstevel@tonic-gate
63*0Sstevel@tonic-gate /*
64*0Sstevel@tonic-gate * First of all, let's don't run with superuser privileges.
65*0Sstevel@tonic-gate */
66*0Sstevel@tonic-gate if (getuid() == 0 || geteuid() == 0) {
67*0Sstevel@tonic-gate if ((pwd = getpwnam(UNPRIV_NAME)) && pwd->pw_uid > 0) {
68*0Sstevel@tonic-gate setgid(pwd->pw_gid);
69*0Sstevel@tonic-gate setuid(pwd->pw_uid);
70*0Sstevel@tonic-gate } else {
71*0Sstevel@tonic-gate setgid(UNPRIV_UGID);
72*0Sstevel@tonic-gate setuid(UNPRIV_UGID);
73*0Sstevel@tonic-gate }
74*0Sstevel@tonic-gate }
75*0Sstevel@tonic-gate
76*0Sstevel@tonic-gate /*
77*0Sstevel@tonic-gate * Redirect our standard input through the raw finger command.
78*0Sstevel@tonic-gate */
79*0Sstevel@tonic-gate if (putenv(path)) {
80*0Sstevel@tonic-gate fprintf(stderr, "%s: putenv: out of memory", argv[0]);
81*0Sstevel@tonic-gate exit(1);
82*0Sstevel@tonic-gate }
83*0Sstevel@tonic-gate argv[0] = FINGER_PROGRAM;
84*0Sstevel@tonic-gate finger_pid = pipe_stdin(argv);
85*0Sstevel@tonic-gate
86*0Sstevel@tonic-gate /*
87*0Sstevel@tonic-gate * Don't wait forever (Peter Wemm <peter@gecko.DIALix.oz.au>).
88*0Sstevel@tonic-gate */
89*0Sstevel@tonic-gate signal(SIGALRM, cleanup);
90*0Sstevel@tonic-gate (void) alarm(TIME_LIMIT);
91*0Sstevel@tonic-gate
92*0Sstevel@tonic-gate /*
93*0Sstevel@tonic-gate * Main filter loop.
94*0Sstevel@tonic-gate */
95*0Sstevel@tonic-gate while ((c = getchar()) != EOF) {
96*0Sstevel@tonic-gate if (input_count++ >= INPUT_LENGTH) { /* don't listen forever */
97*0Sstevel@tonic-gate fclose(stdin);
98*0Sstevel@tonic-gate printf("\n\n Input truncated to %d bytes...\n", input_count - 1);
99*0Sstevel@tonic-gate break;
100*0Sstevel@tonic-gate }
101*0Sstevel@tonic-gate if (c == '\n') { /* good: end of line */
102*0Sstevel@tonic-gate putchar(c);
103*0Sstevel@tonic-gate line_length = 0;
104*0Sstevel@tonic-gate } else {
105*0Sstevel@tonic-gate if (line_length >= LINE_LENGTH) { /* force end of line */
106*0Sstevel@tonic-gate printf("\\\n");
107*0Sstevel@tonic-gate line_length = 0;
108*0Sstevel@tonic-gate }
109*0Sstevel@tonic-gate if (line_length == 0) { /* protect left margin */
110*0Sstevel@tonic-gate putchar(' ');
111*0Sstevel@tonic-gate line_length++;
112*0Sstevel@tonic-gate }
113*0Sstevel@tonic-gate if (isascii(c) && (isprint(c) || isspace(c))) { /* text */
114*0Sstevel@tonic-gate if (c == '\\') {
115*0Sstevel@tonic-gate putchar(c);
116*0Sstevel@tonic-gate line_length++;
117*0Sstevel@tonic-gate }
118*0Sstevel@tonic-gate putchar(c);
119*0Sstevel@tonic-gate line_length++;
120*0Sstevel@tonic-gate } else { /* quote all other thash */
121*0Sstevel@tonic-gate printf("\\%03o", c & 0377);
122*0Sstevel@tonic-gate line_length += 4;
123*0Sstevel@tonic-gate }
124*0Sstevel@tonic-gate }
125*0Sstevel@tonic-gate }
126*0Sstevel@tonic-gate
127*0Sstevel@tonic-gate /*
128*0Sstevel@tonic-gate * Wait until the finger child process has terminated and account for its
129*0Sstevel@tonic-gate * exit status. Which will always be zero on most systems.
130*0Sstevel@tonic-gate */
131*0Sstevel@tonic-gate while ((wait_pid = wait(&finger_status)) != -1 && wait_pid != finger_pid)
132*0Sstevel@tonic-gate /* void */ ;
133*0Sstevel@tonic-gate return (wait_pid != finger_pid || finger_status != 0);
134*0Sstevel@tonic-gate }
135*0Sstevel@tonic-gate
136*0Sstevel@tonic-gate /* perror_exit - report system error text and terminate */
137*0Sstevel@tonic-gate
perror_exit(text)138*0Sstevel@tonic-gate void perror_exit(text)
139*0Sstevel@tonic-gate char *text;
140*0Sstevel@tonic-gate {
141*0Sstevel@tonic-gate perror(text);
142*0Sstevel@tonic-gate exit(1);
143*0Sstevel@tonic-gate }
144*0Sstevel@tonic-gate
145*0Sstevel@tonic-gate /* pipe_stdin - pipe stdin through program (from my ANSI to OLD C converter) */
146*0Sstevel@tonic-gate
pipe_stdin(argv)147*0Sstevel@tonic-gate int pipe_stdin(argv)
148*0Sstevel@tonic-gate char **argv;
149*0Sstevel@tonic-gate {
150*0Sstevel@tonic-gate int pipefds[2];
151*0Sstevel@tonic-gate int pid;
152*0Sstevel@tonic-gate int i;
153*0Sstevel@tonic-gate struct stat st;
154*0Sstevel@tonic-gate
155*0Sstevel@tonic-gate /*
156*0Sstevel@tonic-gate * The code that sets up the pipe requires that file descriptors 0,1,2
157*0Sstevel@tonic-gate * are already open. All kinds of mysterious things will happen if that
158*0Sstevel@tonic-gate * is not the case. The following loops makes sure that descriptors 0,1,2
159*0Sstevel@tonic-gate * are set up properly.
160*0Sstevel@tonic-gate */
161*0Sstevel@tonic-gate
162*0Sstevel@tonic-gate for (i = 0; i < 3; i++) {
163*0Sstevel@tonic-gate if (fstat(i, &st) == -1 && open("/dev/null", 2) != i)
164*0Sstevel@tonic-gate perror_exit("open /dev/null");
165*0Sstevel@tonic-gate }
166*0Sstevel@tonic-gate
167*0Sstevel@tonic-gate /*
168*0Sstevel@tonic-gate * Set up the pipe that interposes the command into our standard input
169*0Sstevel@tonic-gate * stream.
170*0Sstevel@tonic-gate */
171*0Sstevel@tonic-gate
172*0Sstevel@tonic-gate if (pipe(pipefds))
173*0Sstevel@tonic-gate perror_exit("pipe");
174*0Sstevel@tonic-gate
175*0Sstevel@tonic-gate switch (pid = fork()) {
176*0Sstevel@tonic-gate case -1: /* error */
177*0Sstevel@tonic-gate perror_exit("fork");
178*0Sstevel@tonic-gate /* NOTREACHED */
179*0Sstevel@tonic-gate case 0: /* child */
180*0Sstevel@tonic-gate (void) close(pipefds[0]); /* close reading end */
181*0Sstevel@tonic-gate (void) close(1); /* connect stdout to pipe */
182*0Sstevel@tonic-gate if (dup(pipefds[1]) != 1)
183*0Sstevel@tonic-gate perror_exit("dup");
184*0Sstevel@tonic-gate (void) close(pipefds[1]); /* close redundant fd */
185*0Sstevel@tonic-gate (void) execvp(argv[0], argv);
186*0Sstevel@tonic-gate perror_exit(argv[0]);
187*0Sstevel@tonic-gate /* NOTREACHED */
188*0Sstevel@tonic-gate default: /* parent */
189*0Sstevel@tonic-gate (void) close(pipefds[1]); /* close writing end */
190*0Sstevel@tonic-gate (void) close(0); /* connect stdin to pipe */
191*0Sstevel@tonic-gate if (dup(pipefds[0]) != 0)
192*0Sstevel@tonic-gate perror_exit("dup");
193*0Sstevel@tonic-gate (void) close(pipefds[0]); /* close redundant fd */
194*0Sstevel@tonic-gate return (pid);
195*0Sstevel@tonic-gate }
196*0Sstevel@tonic-gate }
197