.\" $NetBSD: libblacklist.3,v 1.10 2020/03/30 15:47:15 christos Exp $
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Christos Zoulas.
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.Dd March 30, 2020
.Dt LIBBLACKLIST 3
.Os
.Sh NAME
.Nm blacklist_open ,
.Nm blacklist_close ,
.Nm blacklist_r ,
.Nm blacklist ,
.Nm blacklist_sa ,
.Nm blacklist_sa_r
.Nd Blacklistd notification library
.Sh LIBRARY
.Lb libblacklist
.Sh SYNOPSIS
.In blacklist.h
.Ft struct blacklist *
.Fn blacklist_open "void"
.Ft void
.Fn blacklist_close "struct blacklist *cookie"
.Ft int
.Fn blacklist "int action" "int fd" "const char *msg"
.Ft int
.Fn blacklist_r "struct blacklist *cookie" "int action" "int fd" "const char *msg"
.Ft int
.Fn blacklist_sa "int action" "int fd" "const struct sockaddr *sa" "socklen_t salen" "const char *msg"
.Ft int
.Fn blacklist_sa_r "struct blacklist *cookie" "int action" "int fd" "const struct sockaddr *sa" "socklen_t salen" "const char *msg"
.Sh DESCRIPTION
These functions can be used by daemons to notify
.Xr blacklistd 8
about successful and failed remote connections so that blacklistd can
block or release port access to prevent Denial of Service attacks.
.Pp
The function
.Fn blacklist_open
creates the necessary state to communicate with
.Xr blacklistd 8
and returns a pointer to it, or
.Dv NULL
on failure.
.Pp
The
.Fn blacklist_close
function frees all memory and resources used.
.Pp
The
.Fn blacklist
function sends a message to
.Xr blacklistd 8 ,
with an integer
.Ar action
argument specifying the type of notification,
a file descriptor
.Ar fd
specifying the accepted file descriptor connected to the client,
and an optional message in the
.Ar msg
argument.
.Pp
The
.Ar action
parameter can take these values:
.Bl -tag -width ".Va BLACKLIST_ABUSIVE_BEHAVIOR"
.It Va BLACKLIST_AUTH_FAIL
There was an unsuccessful authentication attempt.
.It Va BLACKLIST_AUTH_OK
A user successfully authenticated.
.It Va BLACKLIST_ABUSIVE_BEHAVIOR
The sending daemon has detected abusive behavior
from the remote system.
The remote address should
be blocked as soon as possible.
.It Va BLACKLIST_BAD_USER
The sending daemon has determined the username
presented for authentication is invalid.
The
.Xr blacklistd 8
daemon compares the username to a configured list of forbidden
usernames and
blocks the address immediately if a forbidden username matches.
(The
.Ar BLACKLIST_BAD_USER
support is not currently available.)
.El
.Pp
The
.Fn blacklist_r
function is more efficient because it keeps the blacklist state around.
.Pp
The
.Fn blacklist_sa
and
.Fn blacklist_sa_r
functions can be used with unconnected sockets, where
.Xr getpeername 2
will not work, the server will pass the peer name in the message.
.Pp
In all cases the file descriptor passed in the
.Fa fd
argument must be pointing to a valid socket so that
.Xr blacklistd 8
can establish ownership of the local endpoint
using
.Xr getsockname 2 .
.Pp
By default,
.Xr syslogd 8
is used for message logging.
The internal
.Fn bl_create
function can be used to create the required internal
state and specify a custom logging function.
.Sh RETURN VALUES
The function
.Fn blacklist_open
returns a cookie on success and
.Dv NULL
on failure setting
.Dv errno
to an appropriate value.
.Pp
The functions
.Fn blacklist ,
.Fn blacklist_sa ,
and
.Fn blacklist_sa_r
return
.Dv 0
on success and
.Dv \-1
on failure setting
.Dv errno
to an appropriate value.
.Sh SEE ALSO
.Xr blacklistd.conf 5 ,
.Xr blacklistd 8
.Sh AUTHORS
.An Christos Zoulas