IP2UNIX(1)

IP2Unix Manual

IP2UNIX(1)

NAME¶

ip2unix - Turn IP sockets into Unix domain sockets

SYNOPSIS¶

ip2unix [-v...] [-p] {-r RULE | -f FILE} [-r RULE | -f FILE]... PROGRAM [ARGS...]
ip2unix [-v...] [-p] -c {-r RULE | -f FILE} [-r RULE | -f FILE]...
ip2unix -h
ip2unix --version

DESCRIPTION¶

Executes a program and converts IP to Unix domain sockets at runtime via LD_PRELOAD (see ld.so(8)) based on a list of rules, either given via short command line options (see RULE SPECIFICATION) or via a file containing a list of rules separated via newline. The first matching rule causes ip2unix to replace the current IP socket with a Unix domain socket based on the options given. For example if a path is specified, the Unix domain socket will bind or listen to the file given.

OPTIONS¶

-c, --check

This is to validate whether the given rules are correct and the program just prints all validation errors to stderr and exits with exit code 0 if validation was successful and 1 if not.

-h, --help

Show command line usage and exit.

--version

Show version information and exit.

-p, --print

Print out the rules that are in effect in a tabular format. If you do not want to run the PROGRAM, you can use the -c option to exit after printing the rules.

-r, --rule=RULE

A single rule for one particular socket to match. Can be specified multiple times to add more rules.

-f, --file=FILE

Read rules from FILE, which contains a newline-separated list of rules as specified via -r. Empty lines as well as lines starting with # are skipped. Whitespace characters at the beginning of each line are stripped as well.

-v, --verbose

Increases the level of verbosity, according to the following table:

FATAL (default)

Only print fatal errors which cause program termination.

ERROR (-v)

Also print errors that are recoverable.

WARNING (-vv)

Also print messages that might indicate possible problems.

INFO (-vvv)

Also print informational messages about ip2unix behavior.

DEBUG (-vvvv)

Also show messages about ip2unix internals along with source information.

TRACE (-vvvvv)

Print every log message possible.

RULE SPECIFICATION¶

Arguments specified via -r contain a comma-separated list of matches and a single action of what to do when a match is found. If a value contains a comma (,), it has to be escaped using a backslash (\) character. If you want to have a verbatim backslash character just use two consecutive backslashes instead.

Matches¶

The following matches are available:

in | out

Match either a server-side socket (in), a client-side socket (out) or both if neither in nor out is specified.

tcp | udp | stream | d[ata]gram

Match the socket type, which currently is either a stream (alias: tcp) or datagram (aliases: dgram or udp).

addr[ess]=ADDRESS

The IP address to match, which can be either an IPv4 or an IPv6 address.

port=PORT[-PORT_END]

Match the UDP or TCP port number which for outgoing connections specifies the target port and for incomping connections the port that the socket is bound to.

If a range is specified by separating two port numbers via -, the given range is matched instead of just a single port. The range is inclusive, so if 2000-3000 is specified, both port 2000 and port 3000 are matched as well.

from-unix=PATTERN

Use an existing Unix domain socket with a filename matching PATTERN. This is useful for example if a program hardcodes the socket path and you want to change it.

The syntax for PATTERN is similar to glob(7) and allows the following wildcards:

?	Match any single character except /
*	Match zero or more characters except /
**	Match zero or more path components, eg. a/**/z matches a/z, a/b/z, a/b/cde/z, a/b/c/c/d/z and so on
[...]	Match a single character via a series of either verbatim characters or ranges, eg. [a-cijq-s] matches either a, b, c, i, j, q, r or s
[!...]	Same as above, but negates the match
\X	Remove the special meaning of the character X, eg. \? literally matches ?

from-abstract=PATTERN

Similar to from-unix but matches PATTERN against an abstract socket name.

Actions¶

reject[=ERRNO]

Reject calls to connect and bind with EACCES by default or the ERRNO specified either via name or as an integer.

blackhole

Turn the socket into a Unix domain socket but do not make it available for clients to connect. This is useful to deactivate certain sockets without causing errors in the application (unlike reject).

Technically, this means that we bind to a Unix socket using a temporary file system path and unlink it shortly thereafter.

ignore

Prevent a socket from being converted to a Unix domain socket if this is set. This is useful to exempt specific sockets from being matched when another rule matches a broad scope.

path=SOCKET_PATH

Convert the socket into a Unix domain socket at the file specified by SOCKET_PATH, which is either created during bind or used as the target when connecting.

Placeholders are allowed here and are substituted accordingly:

%p	port number or unknown if not an IP socket
%a	IP address or unknown if not an IP socket
%t	socket type (tcp, udp or unknown if it’s neither a stream nor datagram socket)
%%	verbatim %

noremove

If this flag is given in conjunction with a path, the socket file is not removed when the socket is closed.

This works around an issue with more complex programs that spawn subprocesses or threads without sharing memory or cloning the file descriptor table. In some scenarios ip2unix might be unable to correctly track sockets and might accidentally remove the socket file too early.

abstract=NAME

Convert the socket into an abstract namespace Unix domain socket. Unlike the path action, the NAME provided here has no connection with file system pathnames. This also means that file system permissions do not apply.

The placeholders supported in path are also supported here.

systemd[=FD_NAME]

Use an existing socket file descriptor provided by systemd instead of creating a new socket.

An optional file descriptor name (FD_NAME) can be specified to distinguish between several socket units. This corresponds to the FileDescriptorName (see systemd.socket(5)) systemd socket option.

RULE MATCHING BEHAVIOUR¶

Each rule is matched in the specified order and the first socket (regardless of specificity) that matches is either turned into a Unix domain socket, blackholed, rejected or ignored depending on the action specified.

If a listening socket is matched by the same rule multiple times, subsequent sockets are automatically blackholed (that is, deactivated without the application noticing). The reason for doing this is that it requires fewer rules for common things, such as for example handling services that bind to both IPv4 and IPv6 addresses.

Let’s say we have someprogram, which binds to 127.0.0.1:1234 and [::1]:1234 in that order. All we need to do here is match on port 1234 and only the first (127.0.0.1:1234) socket will actually bind to /foo/bar, the second ([::1]:1234) will be blackholed and is not reachable:

$ ip2unix -r in,port=1234,path=/foo/bar someprogram

Note that this is only the case if both end up using the same socket path. If instead something like this is used, none of the two sockets is blackholed:

$ ip2unix -r in,port=1234,path=/foo/bar-%a someprogram

This will result in two sockets:

1./foo/bar-127.0.0.1 for the socket originally binding to 127.0.0.1:1234.

2./foo/bar-::1 for the socket originally binding to [::1]:1234.

The reason we blackhole subsequent sockets that lead to the same part is to make the common case less verbose to express.

If we would not blackhole the socket and the matcher would simply fall through to the next rule, the following would be required to achieve the same behaviour that we have in the first example:

$ ip2unix -r in,port=1234,path=/foo/bar -r in,port=1234,blackhole someprogram

EXAMPLES¶

Simple HTTP client/server¶

The following command spawns a small test web server listening on /tmp/test.socket:

$ ip2unix -r in,path=/tmp/test.socket python3 -m http.server 8000

This connects to the above test server listening on /tmp/test.socket and should show a directory listing:

$ ip2unix -r out,path=/tmp/test.socket curl http://1.2.3.4/

More complicated example¶

For example the following could be put into a file given by the -f command line argument:

out,port=53,ignore
out,tcp,path=/run/some.socket
in,addr=1.2.3.4,path=/run/another.socket
in,port=80,address=abcd::1,blackhole
in,port=80,reject=EADDRINUSE
in,tcp,port=22,systemd=ssh

Each line corresponds to a single rule, that is processed in order of appearance and the above example would result in the following:

1.All outgoing connections to port 53 (no matter if it’s TCP or UDP) will not be converted into Unix domain sockets.

2.This rule will redirect all TCP connections except to port 53 (see above) to use the Unix domain socket at /run/some.socket.

3.Matches the socket that listens to any port on the IPv4 address 1.2.3.4 and instead binds it to the Unix domain socket at /run/another.socket.

4.The application may bind to the IPv6 address abcd::1 on port 80 but it will not receive any connections, because no socket path exists.

5.Trying to bind to port 80 on addresses other than abcd::1 will result in an EADDRINUSE error.

6.Will prevent the TCP socket that would listen on port 22 to not listen at all and instead use the systemd-provided file descriptor named ssh for operations like accept(2).

The same can be achieved solely using -r commandline arguments:

$ ip2unix -r out,port=53,ignore \


          -r out,tcp,path=/run/some.socket \


          -r in,addr=1.2.3.4,path=/run/another.socket \


          -r in,port=80,address=abcd::1,blackhole \


          -r in,port=80,reject=EADDRINUSE \


          -r in,tcp,port=22,systemd=ssh

LIMITATIONS¶

•The program uses LD_PRELOAD (see ld.so(8)), so it will only work with programs that are dynamically linked against the C library. Using ip2unix on statically linked executables or on executables that don’t use the socket family functions of the C library (like Go programs) will not work at the moment.

•If a client which is already using Unix datagram sockets sends packets via sendto or sendmsg to a socket provided by ip2unix without binding first, ip2unix is not able to identify the peer and will subsequently reject the packet. This is not the case when using ip2unix itself on the the client side and it also does not seem to be very common as the author so far did not find such an application in the wild.

However, if this really is an issue to you, the recommended workaround is either to use ip2unix to wrap the client (if it supports IP sockets) or fix the server to natively use Unix domain sockets.

AUTHOR¶

Written by aszlig <aszlig@nix.build>

COPYRIGHT¶

This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

November 2018

IP2Unix 2.2.1

Source file:	ip2unix.1.en.gz (from ip2unix 2.2.1-2.1)
Source last updated:	2024-04-14T20:37:32Z
Converted to HTML:	2024-05-05T01:26:57Z