better manpage again

[authbind.git] / authbind.1

diff --git a/authbind.1 b/authbind.1
index 8d6c335be462c92ec7343408bdfbace7532904b9..d73e998990a92e6139d5c2ef6165f7aaac8e0569 100644 (file)
--- a/authbind.1
+++ b/authbind.1
@@ -17,8 +17,6 @@
 .\" along with this program; if not, write to the Free Software Foundation,
 .\" Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. 
 .\"
 .\" 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
 .TH AUTHBIND 1 "30th August 1998" "Debian Project" "Debian Linux manual"
 .SH NAME 
 authbind \- bind sockets to privileged ports without root


@@ -84,10 +82,29 @@ call, usually
 .RI ( "Permission denied" ).
 .PP
 Secondly, if that test fails to resolve the matter,
 .RI ( "Permission denied" ).
 .PP
 Secondly, if that test fails to resolve the matter,

+.BI /etc/authbind/byaddr/ addr , port
+(any protocol) or failing that

 .BI /etc/authbind/byaddr/ addr : port
 .BI /etc/authbind/byaddr/ addr : port

-is tested, in the same manner as above.
+(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
 .PP

-Thirdly, if the question is still unresolved, the file
+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
+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
 .BI /etc/authbind/byuid/ uid
 will be opened and read.  If the file does not exist then the binding
 is not authorised and


@@ -97,15 +114,24 @@ will return
 .RI ( "Operation not permitted" ", or " "Not owner" ).
 If the file does exist it will be searched for a line of the form
 .nf
 .RI ( "Operation not permitted" ", or " "Not owner" ).
 If the file does exist it will be searched for a line of the form
 .nf

-.IB            addr / length : min\-port , 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
 .fi

-matching the request (ie, 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
 .I length
 bits of
 .I addr
 match those in the proposed
 .B bind

-call, and the proposed port number lies is in the inclusive range
+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 bind
 specified.  If such a line is found then the binding is authorised.
 Otherwise it is not, and
 .B bind


@@ -113,15 +139,6 @@ will fail with
 .B ENOENT
 .RI ( "No such file or directory" ).
 .PP
 .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.
-.PP

 If a read error occurs, or the directory
 .B /etc/authbind
 cannot be accessed, then not only will
 If a read error occurs, or the directory
 .B /etc/authbind
 cannot be accessed, then not only will


@@ -129,11 +146,51 @@ cannot be accessed, then not only will
 fail, but an error message will be printed to stderr.  Unrecognised
 lines in
 .BI /etc/authbind/byuid/ uid
 fail, but an error message will be printed to stderr.  Unrecognised
 lines in
 .BI /etc/authbind/byuid/ uid

-files are silently ignored (as are lines whose
+files are silently ignored, as are lines whose

 .I addr
 has non-zero bits more than
 .I length
 .I addr
 has non-zero bits more than
 .I length

-from the top).
+from the top or where some
+.I min
+is larger than
+.IR max .
+.SH EXAMPLE
+So for example an attempt by uid 432
+to bind to port 80 of address [2620:106:e002:f00f::21]
+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
+.SH PORTS 512-1023
+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, authbind
+will expect the permission files to have an additional
+.B !
+at the start of their leafname.

 .SH MECHANISM
 The shared library loaded using
 .B LD_PRELOAD
 .SH MECHANISM
 The shared library loaded using
 .B LD_PRELOAD


@@ -178,7 +235,8 @@ the program's stderr, was well as returning -1 from
 .BR bind .
 .SH BUGS
 .B authbind
 .BR bind .
 .SH BUGS
 .B authbind

-currently only supports IPv4 sockets.  Programs which open other kinds
+currently only supports IPv4 and IPv6 sockets.
+Programs which open other kinds

 of sockets will not benefit from
 .BR authbind ,
 but it won't get in their way.
 of sockets will not benefit from
 .BR authbind ,
 but it won't get in their way.


@@ -190,6 +248,13 @@ makes an
 installation specific to a particular C library.  This version is for
 GNU/Linux libc6 (glibc2).
 .PP
 installation specific to a particular C library.  This version is for
 GNU/Linux libc6 (glibc2).
 .PP

+.B authbind
+may not operate correctly with multithreaded programs.  It is
+inherently very difficult (if not impossible) to perform the kind of
+trickery that authbind does while preventing all undesirable
+interactions between authbind's activities and those of (say) a
+threading runtime system.
+.PP

 It is quite possible that
 .B authbind
 and other programs and facilities which use
 It is quite possible that
 .B authbind
 and other programs and facilities which use


@@ -205,7 +270,11 @@ means in this context).
 .B authbind
 is ineffective with setuid programs, because they do not honour
 .B LD_PRELOAD
 .B authbind
 is ineffective with setuid programs, because they do not honour
 .B LD_PRELOAD

-for security reasons.  Of course a setuid-root program does not need
+references outside the system directories, for security reasons.  (In
+fact, setuid programs should not honour
+.B LD_PRELOAD
+at all.)
+Of course a setuid-root program does not need

 .BR authbind ,
 but it might be useful to apply it to program which are setuid to
 another user or setgid.  If the author or builder of such a programs
 .BR authbind ,
 but it might be useful to apply it to program which are setuid to
 another user or setgid.  If the author or builder of such a programs


@@ -214,19 +283,14 @@ wishes it to use authbind they could have it load the
 library explicitly rather than via
 .BR LD_PRELOAD .
 .PP
 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
 .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.
-.PP
-Ports from 512 to 1023 inclusive cannot be used with
-.B authbind
-because that would create a security hole, in conjection with
-.BR rshd .
+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
 .PP
 The access control configuration scheme is somewhat strange.
 .SH FILES AND ENVIRONMENT VARIABLES


@@ -286,7 +350,7 @@ was specified.
 .SH AUTHOR
 .B authbind
 and this manpage were written by Ian Jackson.  They are
 .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
 by him and released under the GNU General Public Licence; there is NO
 WARRANTY.  See
 .B /usr/doc/authbind/copyright