.\" along with this program; if not, write to the Free Software Foundation,
.\" Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
.\"
-.\" $Id$
-.\"
.TH AUTHBIND 1 "30th August 1998" "Debian Project" "Debian Linux manual"
.SH NAME
authbind \- bind sockets to privileged ports without root
.BR /etc/authbind .
.PP
Firstly,
-.BR /etc/authbind/byport/ [ ! ]\fIport\fR
+.BI /etc/authbind/byport/ port
is tested. If this file is accessible for execution to the calling
user, according to
.BR access (2),
.RI ( "Permission denied" ).
.PP
Secondly, if that test fails to resolve the matter,
-.BR /etc/authbind/byaddr/ \fIaddr\fR : [ ! ]\fIport\fR
-is tested, in the same manner as above.
+.BI /etc/authbind/byaddr/ addr , port
+(any protocol) or failing that
+.BI /etc/authbind/byaddr/ addr : port
+(IPv4 only)
+is tested, in the same manner as above. Here
+.I addr
+is as from
+.BR inet_ntop ,
+and
+.I port
+is the (local) TCP or UDP port number, expressed as an unsigned
+integer in the minimal non-zero number of digits.
+.PP
+Thirdly, for IPv6 only: since the textual representation from
+.B inet_ntop
+is complicated to predict, a variant of
+.I addr
+is also tested which does not use the double colon abbreviation:
+each 16-byte chunk expressed in the minimal nonzero number
+of hex digits (i.e. with leading zeroes removed), the chunks
+being separated by colons as is conventional.
.PP
-Thirdly, if the question is still unresolved, the file
-.BR /etc/authbind/byuid/ [ ! ]\fIuid\fR
+Fourthly, if the question is still unresolved, the file
+.BI /etc/authbind/byuid/ uid
will be opened and read. If the file does not exist then the binding
is not authorised and
.B bind
.RI ( "Operation not permitted" ", or " "Not owner" ).
If the file does exist it will be searched for a line of the form
.nf
-.IB addr4 / length : min\-port , max\-port
-.IR addrmin [\fB-\fR addrmax ]\fB:\fR min\-port \fB,\fR max\-port
+.IR addrmin [\fB\-\fR addrmax ]\fB,\fR portmin [\fB\-\fR portmax ]
+.IR addr [\fB/\fR length ]\fB,\fR portmin [\fB\-\fR portmax ]
+.IB addr4 / length : portmin , portmax
.fi
-matching the request. The first form requires that the initial
+matching the request.
+The first form requires that the address lies in the
+relevant range (inclusive at both ends).
+The second and third forms require that the initial
.I length
bits of
.I addr
match those in the proposed
.B bind
-call. The second form requires that the address lies in the
-relevant range (inclusive at both ends). Addresses can
-be in any form acceptable to inet_pton. In both cases
+call. The third form is only available for IPv4 since IPv6 addresses
+contain colons.
+Addresses in the byuid file can
+be in any form acceptable to inet_pton. In all cases
the proposed port number must lie is in the inclusive range
specified. If such a line is found then the binding is authorised.
Otherwise it is not, and
.B ENOENT
.RI ( "No such file or directory" ).
.PP
-In each case above,
-.TP
-.I port
-is the (local) TCP or UDP port number, expressed as an unsigned
-integer in the minimal non-zero number of digits, and
-.TP
-.I addr
-is the (local) IP address, as a dotted quad.
+So for example an attempt by uid 432
+to bind to [2620:106:e002:f00f::21]:80
+would result in authbind calling
+.I access(2)
+on, in order,
+.RS
+.B /etc/authbind/byport/80
+.br
+.B /etc/authbind/byaddr/2620:106:e002:f00f::21,80
+.br
+.B /etc/authbind/byaddr/2620:106:e002:f00f:0:0:0:21,80
+.RE
+If none of these files exist, authbind will read
+.RS
+.B /etc/authbind/byuid/432
+.RE
+and search for a line to permit
+the relevant access; examples of lines which would do so are:
+.RS
+.B 2620:106:e002:f00f::21,80
+.br
+.B ::/0,80
+.RE
.PP
If a read error occurs, or the directory
.B /etc/authbind
.I addr
has non-zero bits more than
.I length
-from the top).
-.TP
+from the top) or where some
+.I min
+is larger than
+.IR max .
+.PP
Authorising binding to ports from 512 to 1023 inclusive is
not recommended. Some protocols (including some versions of NFS)
authorise clients by seeing that they are using a port number in this
range. So by authorising a program to be a server for such a port,
you are also authorising it to impersonate the whole host for those
protocols. To make sure that this isn't done by accident,
-if the port number requested is in the range 512-1023, all the files
-checked and read will have the additional
+if the port number requested is in the range 512-1023, authbind
+will expect the permission files to have an additional
.B !
-character.
+at the start of their leafname.
.SH MECHANISM
The shared library loaded using
.B LD_PRELOAD
library explicitly rather than via
.BR LD_PRELOAD .
.PP
-Some badly-written programs may have trouble because
+Some programs may have trouble because
.B authbind
spawns a child process `under their feet', causing (for example) a
.BR fork (2)
to happen and
.B SIGCHLD
-signal to be delivered. Programs should not rely on standard
-libraries not doing these things.
+signal to be delivered. Unfortunately the Unix API does not make
+it possible to deal with this problem in a sane way.
.PP
The access control configuration scheme is somewhat strange.
.SH FILES AND ENVIRONMENT VARIABLES
.SH AUTHOR
.B authbind
and this manpage were written by Ian Jackson. They are
-Copyright (C)1998
+Copyright (C)1998,2012
by him and released under the GNU General Public Licence; there is NO
WARRANTY. See
.B /usr/doc/authbind/copyright
~ian / authbind.git / blobdiff