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.

AUTHORS

Christos Zoulas