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Manual Pages  — LIBBLACKLIST


blacklist_open, blacklist_close, blacklist_r, blacklist, blacklist_sa blacklist_sa_r – Blacklistd notification library





#include <blacklist.h>

struct blacklist *

blacklist_close(struct blacklist *cookie);

blacklist(int action, int fd, const char *msg);

blacklist_r(struct blacklist *cookie, int action, int fd, const char *msg);

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

blacklist_sa_r(struct blacklist *cookie, int action, int fd, const struct sockaddr *sa, socklen_t salen, const char *msg);


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

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

The blacklist_close() function frees all memory and resources used.

The blacklist() function sends a message to blacklistd(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:
  There was an unsuccessful authentication attempt.
  A user successfully authenticated.
  The sending daemon has detected abusive behavior from the remote system. The remote address should be blocked as soon as possible.
  The sending daemon has determined the username presented for authentication is invalid. The blacklistd(8) daemon compares the username to a configured list of forbidden usernames and blocks the address immediately if a forbidden username matches. (The BLACKLIST_BAD_USER support is not currently available.)

The blacklist_r() function is more efficient because it keeps the blacklist state around.

The blacklist_sa() and blacklist_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.

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.


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

The functions blacklist(), blacklist_sa(), and blacklist_sa_r() return 0 on success and -1 on failure setting errno to an appropriate value.


blacklistd.conf(5), blacklistd(8)


Christos Zoulas

LIBBLACKLIST (3) May 5, 2017

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