| 1 | .TH SERVXCHECK 3
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| 2 | .SH NAME
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| 3 | servxcheck \- Internet service access check
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| 4 | .SH SYNOPSIS
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| 5 | .ft B
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| 6 | .nf
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| 7 | #define _MINIX_SOURCE 1
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| 8 | #include </net/gen/netdb.h>
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| 9 |
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| 10 | int servxcheck(ipaddr_t \fIpeer\fP, const char *\fIservice\fP,
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| 11 | void (*\fIlogf\fP)(int \fIpass\fP, const char *\fIname\fP));
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| 12 | char *servxfile(const char *\fIfile\fP);
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| 13 | .fi
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| 14 | .ft R
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| 15 | .SH DESCRIPTION
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| 16 | .B Servxcheck()
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| 17 | is used by programs like
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| 18 | .B inetd
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| 19 | to perform an access check on the host connected to the other end of the TCP
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| 20 | channel that has IP address
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| 21 | .IR peer .
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| 22 | .PP
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| 23 | .B Servxcheck()
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| 24 | translates the IP address to the
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| 25 | associated host name if necessary, and checks if the host is granted access
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| 26 | as guided by the file
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| 27 | .BR /etc/serv.access .
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| 28 | (See
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| 29 | .BR serv.access (5).)
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| 30 | The service name used to search the access file is passed by the caller as
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| 31 | .IR service .
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| 32 | These names should be the same as the service names in
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| 33 | .BR /etc/services .
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| 34 | .PP
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| 35 | The caller should use the NWIOGTCPCONF ioctl() call to find out what the
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| 36 | IP address of the remote end is. It is wise to bypass the
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| 37 | .B servxcheck()
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| 38 | call if the remote end happens to be the local machine (remaddr == locaddr),
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| 39 | so that local connections aren't impeded by slow checks.
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| 40 | .B Servxcheck()
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| 41 | will itself allow connections from 127.0.0.1/8 immediately, so you
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| 42 | don't have to check for that. Example of use:
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| 43 | .PP
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| 44 | .RS
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| 45 | .nf
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| 46 | .ta +4n +4n +4n
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| 47 | if (ioctl(fd, NWIOGTCPCONF, &tcpconf) < 0
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| 48 | || tcpconf.nwtc_remaddr == tcpconf.nwtc_locaddr
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| 49 | || servxcheck(tcpconf.nwtc_remaddr, service_name, NULL)
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| 50 | ) {
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| 51 | serve();
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| 52 | }
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| 53 | .fi
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| 54 | .RE
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| 55 | .PP
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| 56 | An attempt to connect to a service is logged if the access is denied. You
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| 57 | can use the special checkword "\fBlog\fP" to also log if access is granted.
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| 58 | Logging will be done with
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| 59 | .B syslog()
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| 60 | at the
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| 61 | .B warning
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| 62 | level.
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| 63 | A syntax error in the access file may be logged under the
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| 64 | .B err
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| 65 | level.
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| 66 | The caller must use
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| 67 | .B openlog()
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| 68 | to set the appropriate logging facility. One may do one's own logging by
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| 69 | supplying a
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| 70 | .I logf
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| 71 | function that will be called by
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| 72 | .B servxcheck
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| 73 | with a first argument that is true if access is granted, false if
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| 74 | denied, and a second argument that is the name of the remote host whose
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| 75 | access has been checked.
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| 76 | .PP
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| 77 | The default is to fail the check unless the access file says otherwise.
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| 78 | Strange errors make the check succeed. (We do not want
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| 79 | remote access to fail because of some system error.) Note that this
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| 80 | function is not meant to check access to the system, that's what
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| 81 | passwords and such are for, but only to limit access to those who are
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| 82 | allowed to use the services the system offers.
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| 83 | .PP
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| 84 | Connections from a machine to itself are accepted immediately. No further
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| 85 | checks, no logging.
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| 86 | .PP
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| 87 | .B Servxfile()
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| 88 | may be used to specify a file other than the default
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| 89 | .BR /etc/serv.access .
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| 90 | This is useful for programs started from
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| 91 | .B inetd
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| 92 | that want to handle the access check themselves, using a private access file.
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| 93 | The return value of
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| 94 | .B servxfile()
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| 95 | is the pathname of the old access file. Only a pointer to the new path is
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| 96 | saved, the caller must keep the string it points to intact.
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| 97 | .SH FILES
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| 98 | .TP 25n
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| 99 | .B /etc/serv.access
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| 100 | Default access check file.
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| 101 | .SH "SEE ALSO"
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| 102 | .BR syslog (3),
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| 103 | .BR serv.access (5),
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| 104 | .BR services (5),
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| 105 | .BR inetd (8).
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| 106 | .SH DIAGNOSTICS
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| 107 | .B Servxcheck()
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| 108 | returns 0 if the access is denied, 1 if granted.
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| 109 | .PP
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| 110 | Typical syslog message:
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| 111 | .PP
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| 112 | .RS
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| 113 | Jan 10 20:27:20 flotsam inetd[174]: service 'shell' granted to jetsam.cs.vu.nl
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| 114 | .RE
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| 115 | .SH BUGS
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| 116 | IP and DNS based access checks will stop most crackers, but not the really
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| 117 | determined ones. Luckily MINIX 3 is sufficiently strange to thwart the well
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| 118 | known cracking schemes. But don't ever allow yourself to feel secure.
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| 119 | .SH AUTHOR
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| 120 | Kees J. Bot <kjb@cs.vu.nl>
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