LIBBLOCKLIST(3)

LIBBLOCKLIST(3) | Library Functions Manual | LIBBLOCKLIST(3)

# NAME

`blocklist_open`, `blocklist_open2`, `blocklist_close`, `blocklist_r`, `blocklist`, `blocklist_sa`, `blocklist_sa_r` — Blocklistd notification library

# LIBRARY

library “libblocklist”

# SYNOPSIS

`#include <blocklist.h>`

struct blocklist *
`blocklist_open`(void);

struct blocklist *
`blocklist_open2`(void (*logger)(int, struct syslog_data *, va_list));

void
`blocklist_close`(struct blocklist *cookie);

int
`blocklist`(int action, int fd, const char *msg);

int
`blocklist_r`(struct blocklist *cookie, int action, int fd, const char *msg);

int
`blocklist_sa`(int action, int fd, const struct sockaddr *sa, socklen_t salen, const char *msg);

int
`blocklist_sa_r`(struct blocklist *cookie, int action, int fd, const struct sockaddr *sa, socklen_t salen, const char *msg);

# DESCRIPTION

These functions can be used by daemons to notify blocklistd(8) about successful and failed remote connections so that blocklistd can block or release port access to prevent Denial of Service attacks.

The function `blocklist_open`() creates the necessary state to communicate with blocklistd(8) and returns a pointer to it, or `NULL` on failure.

The function `blocklist_open2`() is similar to `blocklist_open`() but allows a logger to be specified. If the logger is `NULL`, then no logging is performed.

The `blocklist_close`() function frees all memory and resources used.

The `blocklist`() function sends a message to blocklistd(8), with an integer action argument specifying the type of notification, a file descriptor fd specifying the accepted file descriptor connected to the client, and an optional message in the msg argument.

The action parameter can take these values:

BLOCKLIST_BAD_USER
  The sending daemon has determined the username presented for authentication is invalid. This is considered as one failure count.
BLOCKLIST_AUTH_FAIL
  There was an unsuccessful authentication attempt. This is considered as two failure counts together.
BLOCKLIST_ABUSIVE_BEHAVIOR
  The sending daemon has detected abusive behavior from the remote system. This is considered as a total immediate failure. The remote address will be blocked as soon as possible.
BLOCKLIST_AUTH_OK
  A valid user successfully authenticated. Any entry for the remote address will be removed as soon as possible.

The `blocklist_r`() function is more efficient because it keeps the blocklist state around.

The `blocklist_sa`() and `blocklist_sa_r`() functions can be used with unconnected sockets, where getpeername(2) will not work, the server will pass the peer name in the message.

In all cases the file descriptor passed in the fd argument must be pointing to a valid socket so that blocklistd(8) can establish ownership of the local endpoint using getsockname(2).

By default, syslogd(8) is used for message logging. The internal `bl_create`() function can be used to create the required internal state and specify a custom logging function.

# RETURN VALUES

The function `blocklist_open`() returns a cookie on success and `NULL` on failure setting `errno` to an appropriate value.

The functions `blocklist`(), `blocklist_sa`(), and `blocklist_sa_r`() return `0` on success and `-1` on failure setting `errno` to an appropriate value.

# SEE ALSO

blocklistd.conf(5), blocklistd(8)

# AUTHORS

Christos Zoulas

February 5, 2025 | NetBSD 11.0