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/*
* Copyright (c) 1980 Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
char copyright[] =
"@(#) Copyright (c) 1980 Regents of the University of California.\n"
"All rights reserved.\n";
/*
* From: @(#)comsat.c 5.24 (Berkeley) 2/25/91
*/
char rcsid[] =
"$Id: comsat.c,v 1.17 1999/10/17 23:18:47 dholland Exp $";
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/file.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <stdio.h>
#include <utmp.h>
#include <termios.h>
#include <signal.h>
#include <errno.h>
#include <netdb.h>
#include <syslog.h>
#include <ctype.h>
#include <string.h>
#include <pwd.h>
#include <paths.h> /* used for _PATH_MAILDIR, _PATH_UTMP, etc. */
#include <unistd.h>
#include <stdlib.h>
#include <time.h>
#include "../version.h"
static int debug = 0;
#define dsyslog if (debug) syslog
#define MAXIDLE 120
static char hostname[MAXHOSTNAMELEN];
static struct utmp *utmp = NULL;
static time_t lastmsgtime;
static int nutmp;
static void mailfor(char *name);
static void notify(struct utmp *utp, off_t offset, const char *filename);
static void jkfprintf(FILE *, const char *name, off_t offset, const char *cr, const char *filename);
static void onalrm(int);
int main(void) {
char msgbuf[100]; /* network input buffer */
struct sockaddr_in from; /* name of socket */
socklen_t fromlen; /* holds sizeof(from) */
/*
* Verify proper invocation: get the address of the local socket
* that's supposed to be our stdin. If it's not a socket (the only
* likely error) assume we were inadvertently run from someone's
* shell and quit out.
*/
fromlen = sizeof(from);
if (getsockname(0, (struct sockaddr *)&from, &fromlen) < 0) {
fprintf(stderr, "comsat: getsockname: %s.\n", strerror(errno));
exit(1);
}
/*
* openlog() opens a connection to the system logger for comsat.
* We log as "comsat", with the process id, to the "LOG_DAEMON"
* log channel.
*/
openlog("comsat", LOG_PID, LOG_DAEMON);
/*
* Schlep over to the system mail spool.
*/
if (chdir(_PATH_MAILDIR)) {
syslog(LOG_ERR, "chdir: %s: %m", _PATH_MAILDIR);
exit(1);
}
/*
* Record the time of the last message received (the one that
* caused us to be run) so we can idle out later.
*/
time(&lastmsgtime);
/*
* Grab our hostname for spewing to the user's screen.
*/
gethostname(hostname, sizeof(hostname));
/*
* Make sure we won't get stopped by scribbling on the user's screen.
*/
signal(SIGTTOU, SIG_IGN);
/*
* This declares that we're not interested in child processes'
* exit codes, so they will go away on their own without needing
* to be wait()'d for.
*/
signal(SIGCHLD, SIG_IGN);
/*
* Periodically reread the utmp, starting now.
*/
signal(SIGALRM, onalrm);
onalrm(SIGALRM);
/*
* Loop forever handling biff packets.
*/
for (;;) {
sigset_t sigset;
int cc;
errno = 0;
cc = recv(0, msgbuf, sizeof(msgbuf) - 1, 0);
if (cc <= 0) {
if (errno != EINTR) sleep(1);
continue;
}
if (!nutmp) {
/* utmp is empty: no one is logged in */
continue;
}
/* Make sure we don't get SIGALRM while doing mailfor() */
sigemptyset(&sigset);
sigaddset(&sigset, SIGALRM);
sigprocmask(SIG_BLOCK, &sigset, NULL);
/* null-terminate input */
msgbuf[cc] = 0;
/* update time stamp */
time(&lastmsgtime);
/* biff the user */
mailfor(msgbuf);
/* allow SIGALRM again */
sigprocmask(SIG_UNBLOCK, &sigset, NULL);
}
}
/*
* This function is called at startup and every fifteen seconds while
* we're running, via timer signals.
*/
static void onalrm(int signum) {
static int utmpsize; /* last malloced size for utmp */
static time_t utmpmtime; /* last modification time for utmp */
struct stat statbuf; /* scratch storage for stat() */
struct utmp *uptr;
int maxutmp;
/*
* Defensive programming (this should not happen)
*/
if (signum!=SIGALRM) {
dsyslog(LOG_DEBUG, "wild signal %d\n", signum);
return;
}
/*
* If we've been sitting around doing nothing, go away.
*/
if (time(NULL) - lastmsgtime >= MAXIDLE) {
exit(0);
}
/*
* Come back here in another fifteen seconds.
*/
alarm(15);
/*
* Check the modification time of the utmp file.
*/
if (stat(_PATH_UTMP, &statbuf) < 0) {
dsyslog(LOG_DEBUG, "fstat of utmp failed: %m\n");
return;
}
if (statbuf.st_mtime > utmpmtime) {
/*
* utmp has changed since we last came here; reread it and
* save the modification time.
*/
utmpmtime = statbuf.st_mtime;
/*
* If it's now bigger than the space we have for it,
* get more space.
*/
if (statbuf.st_size > utmpsize) {
utmpsize = statbuf.st_size + 10 * sizeof(struct utmp);
if (utmp) {
utmp = realloc(utmp, utmpsize);
}
else {
utmp = malloc(utmpsize);
}
if (!utmp) {
syslog(LOG_ERR, "malloc failed: %m");
exit(1);
}
}
/* This is how many utmp entries we can possibly get */
maxutmp = utmpsize / sizeof(struct utmp);
/* Rewind the utmp file */
setutent();
/*
* Read the utmp file, via libc, copying each entry and
* counting how many we get.
*/
nutmp = 0;
while ((uptr = getutent())!=NULL && nutmp < maxutmp) {
utmp[nutmp] = *uptr;
nutmp++;
}
/* Now done; close the utmp file. */
endutent();
}
}
/*
* We get here when we have mail to announce for the specified user.
* "name" holds a biff packet, which comes in the form
* username@fileoffset
*/
static void mailfor(char *name)
{
struct utmp *utp;
char *cp;
off_t offset;
char *filename;
dsyslog(LOG_DEBUG, "mailfor: %s\n", name);
/* Break off the file offset part and convert it to an integer. */
cp = strchr(name, '@');
if (!cp) return;
*cp = 0;
offset = strtol(cp + 1, &filename, 10);
/* if(*filename != '\0')
return; */
if(*filename == ':')
filename++;
/* Look through the utmp and call notify() for each matching login. */
utp = &utmp[nutmp];
while (--utp >= utmp) {
if (!strncmp(utp->ut_name, name, sizeof(utmp[0].ut_name)))
notify(utp, offset, filename);
}
}
/*
* Check if a given tty name found in utmp is actually a legitimate tty.
*/
static int valid_tty(const char *line)
{
const char *testline = line;
/*
* As of Linux 2.2 we can now sometimes have ttys in subdirs,
* but only /dev/pts. So if the name begins with pts/, skip that
* part. If there's a slash in anything else, complain loudly.
*/
if (!strncmp(testline, "pts/", 4)) testline += 4;
if (strchr(testline, '/')) {
/* A slash is an attempt to break security... */
return 0;
}
return 1;
}
/*
* This actually writes to the user's terminal.
*/
static void notify(struct utmp *utp, off_t offset, const char *filename)
{
FILE *tp; /* file open on tty */
struct stat stb;
struct termios tbuf;
char tty[sizeof(utp->ut_line)+sizeof(_PATH_DEV)+1]; /* full tty path */
char name[sizeof(utp->ut_name) + 1]; /* user name */
char line[sizeof(utp->ut_line) + 1]; /* tty name */
const char *cr; /* line delimiter */
sigset_t sigset; /* scratch signal mask */
#ifdef USER_PROCESS
if (utp->ut_type != USER_PROCESS) {
return;
}
#endif
/*
* Be careful in case we have a hostile utmp. (Remember sunos4
* where it was mode 666?) Note that ut_line normally includes
* enough space for the null-terminator, but ut_name doesn't.
*/
strncpy(line, utp->ut_line, sizeof(utp->ut_line));
line[sizeof(utp->ut_line)] = 0;
strncpy(name, utp->ut_name, sizeof(utp->ut_name));
name[sizeof(name) - 1] = '\0';
/* Get the full path to the tty. */
snprintf(tty, sizeof(tty), "%s%s", _PATH_DEV, line);
/*
* Again, in case we have a hostile utmp, try to make sure we've
* got valid data and we're not being asked to write to, say,
* /etc/passwd.
*/
if (!valid_tty(line)) {
syslog(LOG_AUTH | LOG_NOTICE, "invalid tty \"%s\" in utmp",
tty);
return;
}
/*
* If the user's tty isn't mode u+x, they don't want biffage;
* skip them.
*/
if (stat(tty, &stb) || !(stb.st_mode & S_IEXEC)) {
dsyslog(LOG_DEBUG, "%s: wrong mode on %s", name, tty);
return;
}
dsyslog(LOG_DEBUG, "notify %s on %s\n", name, tty);
/*
* Fork a child process to do the tty I/O. There are, traditionally,
* various ways for tty I/O to block indefinitely or otherwise hang.
* Also later down we're going to setuid to make sure we can't be
* used to read any file on the system.
*
* This of course makes a denial of service attack possible. So,
* in the parent process, wait a tenth of a second before continuing.
* This causes a primitive form of rate-limiting. It might be too
* much delay for a busy system. But a busy system probably shouldn't
* be using comsat. If someone would like to make this smarter, feel
* free.
*
* Note: sleep with select() and NOT sleep() because on some systems
* at least sleep uses alarm(), which would interfere with our
* reload/timeout logic.
*/
if (fork()) {
/* parent process */
struct timeval tv;
tv.tv_sec = 0;
tv.tv_usec = 100000;
select(0, NULL, NULL, NULL, &tv);
return;
}
/* child process */
/*
* Turn off the alarm handler and instead exit in thirty seconds.
* Make sure SIGALRM isn't blocked.
*/
signal(SIGALRM, SIG_DFL);
sigemptyset(&sigset);
sigprocmask(SIG_SETMASK, &sigset, NULL);
alarm(30);
/*
* Open the tty.
*/
if ((tp = fopen(tty, "w")) == NULL) {
dsyslog(LOG_ERR, "fopen of tty %s failed", tty);
_exit(-1);
}
/*
* Get the tty mode. Try to determine whether to use \n or \r\n
* for linebreaks.
*/
tcgetattr(fileno(tp), &tbuf);
if ((tbuf.c_oflag & OPOST) && (tbuf.c_oflag & ONLCR)) cr = "\n";
else cr = "\r\n";
/*
* Announce the mail.
*/
fprintf(tp, "%s\aNew mail for %s@%.*s\a has arrived:%s----%s",
cr, name, (int)sizeof(hostname), hostname, cr, cr);
/*
* Print the first few lines of the message.
*/
jkfprintf(tp, name, offset, cr, filename);
/*
* Close up and quit the child process.
*/
fclose(tp);
_exit(0);
}
/*
* This prints a few lines from the mailbox of the user "name" at offset
* "offset", using "cr" as the line break string, to the file "tp".
*/
static void jkfprintf(FILE *tp, const char *name, off_t offset, const char *cr, const char * filename)
{
char *cp, ch;
FILE *fi;
int linecnt, charcnt, inheader;
struct passwd *p;
char line[BUFSIZ];
/*
* Set uid to user in case mail drop is on nfs
* ...and also to prevent cute symlink to /etc/shadow games
*/
if ((p = getpwnam(name)) == NULL) {
/*
* If user is not in passwd file, assume that it's
* an attempt to break security...
*/
syslog(LOG_AUTH | LOG_NOTICE, "%s not in passwd file", name);
return;
}
/*
* This sets both real and effective uids and clears the saved uid
* too (see posix) so it's a one-way trip.
*/
setuid(p->pw_uid);
/*
* Open the user's mailbox (recall we're already in the mail spool dir)
*/
fi = fopen(filename, "r");
if (fi == NULL) {
dsyslog(LOG_DEBUG, "couldn't open mailbox %s\n", filename);
return;
}
/* Move to requested offset */
fseek(fi, offset, L_SET);
/*
* Print the first 7 lines or 560 characters of the new mail
* (whichever comes first). Skip header crap other than
* From and Subject.
*/
linecnt = 7;
charcnt = 560;
inheader = 1;
while (fgets(line, sizeof(line), fi) != NULL) {
if (inheader) {
if (line[0] == '\n') {
inheader = 0;
continue;
}
if (line[0] == ' ' || line[0] == '\t' ||
(strncasecmp(line, "From:", 5) &&
strncasecmp(line, "Subject:", 8)))
continue;
}
if (linecnt <= 0 || charcnt <= 0) {
fprintf(tp, "...more...%s", cr);
fclose(fi);
return;
}
/* strip weird stuff so can't trojan horse stupid terminals */
for (cp = line; (ch = *cp) && ch != '\n'; ++cp, --charcnt) {
ch = toascii(ch);
if (!isprint(ch) && !isspace(ch))
ch |= 0x40;
fputc(ch, tp);
}
fputs(cr, tp);
--linecnt;
}
fprintf(tp, "----%s", cr);
fclose(fi);
}
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