.B .noip
in the calling user's home directory, as determined by the
.B HOME
-environment, or, failing that, looking up the
-.I real
-(not effective) user id in the password database.
+environment, or, failing that, looking up the effective user id in the
+password database. However, if the environment variable
+.B NOIP_CONFIG
+is set, then the file it names is read instead (assuming it exists; if
+it doesn't, no configuration is read).
.PP
The configuration file has a simple line-based format. A line is
-ignored if it consists only of whitespace, or if its first whitespace
-character is
+ignored if it consists only of whitespace, or if its first
+non-whitespace character is
.RB ` # '.
Otherwise, the first whitespace-delimited word is a keyword and the
remainder of the line is a value. The following keywords are
.BI "socketdir " directory
Store the Unix-domain sockets in
.IR directory
-rather than the default.
+rather than the default. The environment variable
+.B NOIP_SOCKETDIR
+can also be used to control which directory is used for sockets.
+.TP
+.BI "autoports " min "\-" max
+Select which ports are used for implicit binding. Allocating ports can
+be a bit slow, since checking whether a Unix domain socket is in use is
+difficult. A wide range makes things easier, because
+.B noip
+starts by trying ports at random from the given range. The environment
+variable
+.B NOIP_AUTOPORTS
+can also be used to control which ports are assigned automatically.
.TP
.BI "realbind " acl-entry
-Add an entry to the
+Add a comma-separated list of entries to the
.B realbind
-access control list (ACL). When a program attempts to
+access control list (ACL). (See below for the format of an ACL entry.)
+When a program attempts to
.BR bind (2)
a socket to an address, the
.B realbind
ACL is consulted. If the address is matched, then the program is
allowed to bind a real Internet socket to that address; otherwise, the
-socket is bound to a Unix-domain socket.
+socket is bound to a Unix-domain socket. Three environment variables
+are consulted too:
+.BR NOIP_REALBIND_BEFORE ,
+.BR NOIP_REALBIND ,
+and
+.BR NOIP_REALBIND_AFTER .
+The
+.B _BEFORE
+rules are inserted at the front of the list; the
+.B _AFTER
+rules are appended on the end. Currently, the rules in
+.B NOIP_REALBIND
+are also put at the end (before the
+.B _AFTER
+rules), though this may change later.
.TP
-.BI "realbind " acl-entry
-Add an entry to the
+.BI "realconnect " acl-entry
+Add a comma-separated list of entries to the
.B realconnect
-access control list (ACL). When a program attempts to
+access control list (ACL). (See below for the format of an ACL entry.)
+When a program attempts to
.BR connect (2)
a socket to an address, or to contact another socket using
.BR sendto (2)
.B realconnect
ACL is consulted. If the destination address is matched, then the
program is allowed to contact the real Internet socket; otherwise, the
-attempt is made to contact a Unix-domain socket.
-.PP
+attempt is made to contact a Unix-domain socket. Three environment variables
+are consulted too:
+.BR NOIP_REALCONNET_BEFORE ,
+.BR NOIP_REALCONNECT ,
+and
+.BR NOIP_REALCONNECT_AFTER .
+The
+.B _BEFORE
+rules are inserted at the front of the list; the
+.B _AFTER
+rules are appended on the end. Currently, the rules in
+.B NOIP_REALCONNECT
+are also put at the end (before the
+.B _AFTER
+rules), though this may change later.
+.IP
(Aside: An attempt to connect to a remote host may not be a hopeless failure,
even if a real IP socket is denied:
.B noip
sockets correspond to locally available addresses; and besides, sockets
can be introduced into the directory by other programs simulating remote
servers.)
+.TP
+.BI "impbind " bind-rule
+Add a comma-separated list of entries to the implicit-bind rule list.
+When a program attempts to transmit from a socket \(en e.g., with
+.BR connect (2),
+.BR sendto (2), or
+.BR sendmsg (2)
+\(en without binding its local address first,
+.B noip
+consults this list to decide on the correct local address to assign.
+Each entry in the list has the form
+.RS
+.IP
+.I address-range
+.IR address | \c
+.B same
+.PP
+The rules are tried in order: if the remote address matches (in the same
+way as in an ACL entry) the address range on the left side of the rule,
+then the socket is bound to the address from the right side; if the
+address on the right is
+.B same
+then the remote address is used.
+.PP
+Three environment variables
+are consulted too:
+.BR NOIP_IMPBIND_BEFORE ,
+.BR NOIP_IMPBIND ,
+and
+.BR NOIP_IMPBIND_AFTER .
+The
+.B _BEFORE
+rules are inserted at the front of the list; the
+.B _AFTER
+rules are appended on the end. Currently, the rules in
+.B NOIP_IMPBIND
+are also put at the end (before the
+.B _AFTER
+rules), though this may change later.
+.RE
.PP
An
.I acl-entry
-has this format:
+is a comma-separated list of entries of the form:
.IP
.BR + | \-
-.IR address \c
-.RB [ \- \c
-.IR address | \c
-.BR / \c
-.IR mask ]| \c
-.BR local | any
+.I address-range
.RB [ : \c
-.IR port [ \c
-.BI \- \c
-.IR port ]]
+.IR port-range ]
.PP
(The spaces in the above are optional.)
.PP
-The leading sign says whether
-matching addresses should be
+The leading sign says whether matching addresses should be
.I accepted
.RB (` + ')
or
.I denied
.RB (` \- ').
.PP
-The IP-address portion may be any of the following
+The
+.I address-range
+portion may be any of the following.
.TP
.B any
Matches all addresses.
Matches the address of one of the machine's network interfaces.
.TP
.I address
-Matches just the given address
+Matches just the given IPv4 or IPv6 address. An
+.I address
+may be enclosed in square brackets; IPv6 addresses must be so enclosed,
+because colons are significant in the rest of the ACL syntax.
.TP
.IB address \- address
Matches any address which falls in the given range. Addresses are
compared lexicographically, with octets to the left given precedence
over octets to the right.
.TP
-.IB address / mask
-Matches an address in the given network. The
-.I mask
-may be a netmask in dotted-quad form, or a one-bit-count.
+.IB address / prefix-length
+Matches an address in the given network.
.PP
-The port portion may be omitted (which means `match any port'), or may
-be a single
+The
+.I port-range
+may be omitted (which means `match any port'), or may be a single
.I port
or a range
.IB port \- port
For example, it may be useful to allow access at least to a DNS server.
This can be accomplished by adding a line
.VS
-realconnect +1.2.3.4:52
+realconnect +1.2.3.4:53
.VE
to the configuration file, where 1.2.3.4 is the IP address of one of
your DNS server.
is implemented as an
.B LD_PRELOAD
hack. It won't work on setuid programs. Also, perhaps more
-importantly, it can't do anything a
+importantly, it can't do anything to prevent a
.I malicious
-program use of networking: a program could theoretically issue sockets
+program's use of networking: a program could theoretically issue sockets
system calls directly instead of using the C library calls that
.B noip
intercepts. It is intended only as a tool for enhancing the security of
.PP
This manual is surprisingly long and complicated for such a simple hack.
.SH AUTHOR
-Mark Wooding, <mdw@nsict.org>
+Mark Wooding, <mdw@distorted.org.uk>
~mdw / preload-hacks / blobdiff