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      1 /*
      2  * Pager: Routines to create a "more" running out of a particular file
      3  * descriptor.
      4  *
      5  * Copyright 1987, 1988 by MIT Student Information Processing Board
      6  *
      7  * Permission to use, copy, modify, and distribute this software and
      8  * its documentation for any purpose is hereby granted, provided that
      9  * the names of M.I.T. and the M.I.T. S.I.P.B. not be used in
     10  * advertising or publicity pertaining to distribution of the software
     11  * without specific, written prior permission.  M.I.T. and the
     12  * M.I.T. S.I.P.B. make no representations about the suitability of
     13  * this software for any purpose.  It is provided "as is" without
     14  * express or implied warranty.
     15  */
     16 
     17 #ifdef HAVE_UNISTD_H
     18 #include <unistd.h>
     19 #endif
     20 #ifdef HAVE_ERRNO_H
     21 #include <errno.h>
     22 #else
     23 extern int errno;
     24 #endif
     25 
     26 #include "ss_internal.h"
     27 #include <stdio.h>
     28 #include <sys/types.h>
     29 #include <sys/file.h>
     30 #include <signal.h>
     31 #ifdef HAVE_SYS_PRCTL_H
     32 #include <sys/prctl.h>
     33 #else
     34 #define PR_GET_DUMPABLE 3
     35 #endif
     36 #if (!defined(HAVE_PRCTL) && defined(linux))
     37 #include <sys/syscall.h>
     38 #endif
     39 
     40 static char MORE[] = "more";
     41 extern char *_ss_pager_name;
     42 extern char *getenv PROTOTYPE((const char *));
     43 
     44 char *ss_safe_getenv(const char *arg)
     45 {
     46 	if ((getuid() != geteuid()) || (getgid() != getegid()))
     47 		return NULL;
     48 #if HAVE_PRCTL
     49 	if (prctl(PR_GET_DUMPABLE, 0, 0, 0, 0) == 0)
     50 		return NULL;
     51 #else
     52 #if (defined(linux) && defined(SYS_prctl))
     53 	if (syscall(SYS_prctl, PR_GET_DUMPABLE, 0, 0, 0, 0) == 0)
     54 		return NULL;
     55 #endif
     56 #endif
     57 
     58 #ifdef HAVE___SECURE_GETENV
     59 	return __secure_getenv(arg);
     60 #else
     61 	return getenv(arg);
     62 #endif
     63 }
     64 
     65 /*
     66  * this needs a *lot* of work....
     67  *
     68  * run in same process
     69  * handle SIGINT sensibly
     70  * allow finer control -- put-page-break-here
     71  */
     72 
     73 #ifndef NO_FORK
     74 int ss_pager_create(void)
     75 {
     76 	int filedes[2];
     77 
     78 	if (pipe(filedes) != 0)
     79 		return(-1);
     80 
     81 	switch(fork()) {
     82 	case -1:
     83 		return(-1);
     84 	case 0:
     85 		/*
     86 		 * Child; dup read half to 0, close all but 0, 1, and 2
     87 		 */
     88 		if (dup2(filedes[0], 0) == -1)
     89 			exit(1);
     90 		ss_page_stdin();
     91 	default:
     92 		/*
     93 		 * Parent:  close "read" side of pipe, return
     94 		 * "write" side.
     95 		 */
     96 		(void) close(filedes[0]);
     97 		return(filedes[1]);
     98 	}
     99 }
    100 #else /* don't fork */
    101 int ss_pager_create()
    102 {
    103     int fd;
    104     fd = open("/dev/tty", O_WRONLY, 0);
    105     return fd;
    106 }
    107 #endif
    108 
    109 static int write_all(int fd, char *buf, size_t count)
    110 {
    111 	ssize_t ret;
    112 	int c = 0;
    113 
    114 	while (count > 0) {
    115 		ret = write(fd, buf, count);
    116 		if (ret < 0) {
    117 			if ((errno == EAGAIN) || (errno == EINTR))
    118 				continue;
    119 			return -1;
    120 		}
    121 		count -= ret;
    122 		buf += ret;
    123 		c += ret;
    124 	}
    125 	return c;
    126 }
    127 
    128 void ss_page_stdin()
    129 {
    130 	int i;
    131 	sigset_t mask;
    132 
    133 	for (i = 3; i < 32; i++)
    134 		(void) close(i);
    135 	(void) signal(SIGINT, SIG_DFL);
    136 	sigprocmask(SIG_BLOCK, 0, &mask);
    137 	sigdelset(&mask, SIGINT);
    138 	sigprocmask(SIG_SETMASK, &mask, 0);
    139 	if (_ss_pager_name == (char *)NULL) {
    140 		if ((_ss_pager_name = ss_safe_getenv("PAGER")) == (char *)NULL)
    141 			_ss_pager_name = MORE;
    142 	}
    143 	(void) execlp(_ss_pager_name, _ss_pager_name, (char *) NULL);
    144 	{
    145 		/* minimal recovery if pager program isn't found */
    146 		char buf[80];
    147 		register int n;
    148 		while ((n = read(0, buf, 80)) > 0)
    149 			write_all(1, buf, n);
    150 	}
    151 	exit(errno);
    152 }
    153