pkt_filter.cc

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// Copyright (C) 2013-2024 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
#include <config.h>
#include <dhcp/iface_mgr.h>
#include <dhcp/pkt_filter.h>
 
#include <sys/socket.h>
#include <fcntl.h>
 
namespace isc {
namespace dhcp {
 
int
PktFilter::openFallbackSocket(const isc::asiolink::IOAddress& addr,
                              const uint16_t port) {
    // Create socket.
    int sock = socket(AF_INET, SOCK_DGRAM, 0);
    if (sock < 0) {
        isc_throw(SocketConfigError, "failed to create fallback socket for"
                  " address " << addr << ", port " << port
                  << ", reason: " << strerror(errno));
    }
    // Set the close-on-exec flag.
    if (fcntl(sock, F_SETFD, FD_CLOEXEC) < 0) {
        close(sock);
        isc_throw(SocketConfigError, "Failed to set close-on-exec flag"
                  << " on fallback socket for address " << addr
                  << ", port " << port
                  << ", reason: " << strerror(errno));
    }
    // Bind the socket to a specified address and port.
    struct sockaddr_in addr4;
    memset(&addr4, 0, sizeof(addr4));
    addr4.sin_family = AF_INET;
    addr4.sin_addr.s_addr = htonl(addr.toUint32());
    addr4.sin_port = htons(port);
 
    if (bind(sock, reinterpret_cast<struct sockaddr*>(&addr4),
             sizeof(addr4)) < 0) {
        // Get the error message immediately after the bind because the
        // invocation to close() below would override the errno.
        char* errmsg = strerror(errno);
        // Remember to close the socket if we failed to bind it.
        close(sock);
        isc_throw(SocketConfigError, "failed to bind fallback socket to"
                  " address " << addr << ", port " << port
                  << ", reason: " << errmsg
                  << " - is another DHCP server running?");
    }
 
    // Set socket to non-blocking mode. This is to prevent the read from the
    // fallback socket to block message processing on the primary socket.
    if (fcntl(sock, F_SETFL, O_NONBLOCK) != 0) {
        // Get the error message immediately after the bind because the
        // invocation to close() below would override the errno.
        char* errmsg = strerror(errno);
        close(sock);
        isc_throw(SocketConfigError, "failed to set SO_NONBLOCK option on the"
                  " fallback socket, bound to " << addr << ", port "
                  << port << ", reason: " << errmsg);
    }
    // Successfully created and bound a fallback socket. Return a descriptor.
    return (sock);
}
 
} // end of isc::dhcp namespace
} // end of isc namespace