network.c

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/*
 *   This program is is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or (at
 *   your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/**
 * $Id: 48fda491369cb10dc471045f89e858d6976eed62 $
 * @file lib/bio/network.c
 * @brief BIO patricia trie filtering handlers
 *
 * @copyright 2024 Network RADIUS SAS (legal@networkradius.com)
 */
 
#include <freeradius-devel/util/value.h>
#include <freeradius-devel/util/trie.h>
 
#include <freeradius-devel/bio/bio_priv.h>
#include <freeradius-devel/bio/fd_priv.h>
 
#include <freeradius-devel/bio/network.h>
 
/** The network filtering bio
 */
typedef struct {
        FR_BIO_COMMON;
 
        fr_bio_read_t   discard;        //!< callback to run when discarding a packet due to filtering
 
        size_t          offset;         //!< where #fr_bio_fd_packet_ctx_t is stored
 
        fr_trie_t const *trie;          //!< patricia trie for filtering
} fr_bio_network_t;
 
/** Read a UDP packet, and only return packets from allowed sources.
 *
 */
static ssize_t fr_bio_network_read(fr_bio_t *bio, void *packet_ctx, void *buffer, size_t size)
{
        ssize_t rcode;
        bool *value;
        fr_bio_network_t *my = talloc_get_type_abort(bio, fr_bio_network_t);
        fr_bio_fd_packet_ctx_t *addr;
        fr_bio_t *next;
        
        next = fr_bio_next(&my->bio);
        fr_assert(next != NULL);
 
        rcode = next->read(next, packet_ctx, buffer, size);
        if (rcode <= 0) return rcode;
 
        if (!packet_ctx) return rcode;
 
        addr = fr_bio_fd_packet_ctx(my, packet_ctx);
 
        /*
         *      Look up this particular source.  If it's not found, then we suppress this packet.
         */
        value = fr_trie_lookup_by_key(my->trie,
                                      &addr->socket.inet.src_ipaddr.addr, addr->socket.inet.src_ipaddr.prefix);
        if (value != FR_BIO_NETWORK_ALLOW) {
                if (my->discard) return my->discard(bio, packet_ctx, buffer, rcode);
                return 0;
        }
 
        return rcode;
}
 
 
/** Allocate a bio for filtering IP addresses
 *
 *  This is used for unconnected UDP bios, where we filter packets based on source IP address.
 *
 *  It is also used for accept bios, where we filter new connections based on source IP address.  The caller
 *  should chain this bio to the next FD bio, and then fr_bio_read() from the top-level bio.  The result will
 *  be filtered or "clean" FDs.
 *
 *  A patricia trie (but not the bio) could also be used in an haproxy "activate" callback, where the callback
 *  gets the haproxy socket info, and then checks if the source is allowed.  However, that patricia trie is a
 *  property of the main "accept" bio, and should be managed by the activate() callback for the haproxy bio.
 */
fr_bio_t *fr_bio_network_alloc(TALLOC_CTX *ctx, fr_ipaddr_t const *allow, fr_ipaddr_t const *deny,
                               fr_bio_read_t discard, fr_bio_t *next)
{
        fr_bio_network_t *my;
        fr_bio_t *fd;
        fr_bio_fd_info_t const *info;
 
        /*
         *      We are only usable for FD bios.  We need to get "offset" into the packet_ctx, and we don't
         *      want to have an API which allows for two different "offset" values to be passed to two
         *      different bios.
         */
        fd = NULL;
 
        /*
         *      @todo - add an internal "type" to the bio?
         */
        do {
                if (strcmp(talloc_get_name(next), "fr_bio_fd_t") == 0) {
                        fd = next;
                        break;
                }
        } while ((next = fr_bio_next(next)) != NULL);
 
        if (!fd) return NULL;
 
        info = fr_bio_fd_info(fd);
        fr_assert(info != NULL);
 
        /*
         *      We can only filter connections for IP address families.
         *
         *      Unix domain sockets have to use a different method for filtering input connections.
         */
        if (!((info->socket.af == AF_INET) || (info->socket.af == AF_INET6))) return NULL;
 
        /*
         *      We can only be used for accept() sockets, or unconnected UDP sockets.
         */
        switch (info->type) {
        case FR_BIO_FD_UNCONNECTED:
                break;
 
        case FR_BIO_FD_CONNECTED:
                return NULL;
 
        case FR_BIO_FD_ACCEPT:
                break;
        }
 
        my = talloc_zero(ctx, fr_bio_network_t);
        if (!my) return NULL;
 
        my->offset = ((fr_bio_fd_t *) fd)->offset;
        my->discard = discard;
 
        my->bio.write = fr_bio_next_write;
        my->bio.read = fr_bio_network_read;
 
        my->trie = fr_bio_network_trie_alloc(my, info->socket.af, allow, deny);
        if (!my->trie) {
                talloc_free(my);
                return NULL;
        }
 
        fr_bio_chain(&my->bio, next);
 
        return (fr_bio_t *) my;
}
 
/** Create a patricia trie for doing network filtering.
 *
 */
fr_trie_t *fr_bio_network_trie_alloc(TALLOC_CTX *ctx, int af, fr_ipaddr_t const *allow, fr_ipaddr_t const *deny)
{
        size_t i, num;
        fr_trie_t *trie;
 
        trie = fr_trie_alloc(ctx, NULL, NULL);
        if (!trie) return NULL;
 
        num = talloc_array_length(allow);
        fr_assert(num > 0);
 
        for (i = 0; i < num; i++) {
                bool *value;
 
                /*
                 *      Can't add v4 networks to a v6 socket, or vice versa.
                 */
                if (allow[i].af != af) {
                        fr_strerror_printf("Address family in entry %zd - 'allow = %pV' "
                                           "does not match 'ipaddr'", i + 1, fr_box_ipaddr(allow[i]));
                fail:
                        talloc_free(trie);
                        return NULL;
                }
 
                /*
                 *      Duplicates are bad.
                 */
                value = fr_trie_match_by_key(trie, &allow[i].addr, allow[i].prefix);
                if (value) {
                        fr_strerror_printf("Cannot add duplicate entry 'allow = %pV'",
                                           fr_box_ipaddr(allow[i]));
                        goto fail;
                }
 
#if 0
                /*
                 *      Look for overlapping entries.  i.e. the networks MUST be disjoint.
                 *
                 *      Note that this catches 192.168.1/24 followed by 192.168/16, but NOT the other way
                 *      around.  The best fix is likely to add a flag to fr_trie_alloc() saying "we can only
                 *      have terminal fr_trie_user_t nodes"
                 */
                value = fr_trie_lookup_by_key(trie, &allow[i].addr, allow[i].prefix);
                if (network && (network->prefix <= allow[i].prefix)) {
                        fr_strerror_printf("Cannot add overlapping entry 'allow = %pV'", fr_box_ipaddr(allow[i]));
                        fr_strerror_const("Entry is completely enclosed inside of a previously defined network.");
                        goto fail;
                }
#endif
 
                /*
                 *      Insert the network into the trie.  Lookups will return a bool ptr of allow / deny.
                 */
                if (fr_trie_insert_by_key(trie, &allow[i].addr, allow[i].prefix, FR_BIO_NETWORK_ALLOW) < 0) {
                        fr_strerror_printf("Failed adding 'allow = %pV' to filtering rules", fr_box_ipaddr(allow[i]));
                        return NULL;
                }
        }
 
        /*
         *      And now check denied networks.
         */
        num = talloc_array_length(deny);
        if (!num) return trie;
 
        /*
         *      Since the default is to deny, you can only add a "deny" inside of a previous "allow".
         */
        for (i = 0; i < num; i++) {
                bool *value;
 
                /*
                 *      Can't add v4 networks to a v6 socket, or vice versa.
                 */
                if (deny[i].af != af) {
                        fr_strerror_printf("Address family in entry %zd - 'deny = %pV' "
                                           "does not match 'ipaddr'", i + 1, fr_box_ipaddr(deny[i]));
                        goto fail;
                }
 
                /*
                 *      Exact duplicates are forbidden.
                 */
                value = fr_trie_match_by_key(trie, &deny[i].addr, deny[i].prefix);
                if (value) {
                        fr_strerror_printf("Cannot add duplicate entry 'deny = %pV'", fr_box_ipaddr(deny[i]));
                        goto fail;
                }
 
                /*
                 *      A "deny" can only be within a previous "allow".
                 */
                value = fr_trie_lookup_by_key(trie, &deny[i].addr, deny[i].prefix);             
                if (!value) {
                        fr_strerror_printf("The network in entry %zd - 'deny = %pV' is not "
                                           "contained within a previous 'allow'", i + 1, fr_box_ipaddr(deny[i]));
                        goto fail;
                }
 
                /*
                 *      A "deny" cannot be within a previous "deny".
                 */
                if (value == FR_BIO_NETWORK_DENY) {
                        fr_strerror_printf("The network in entry %zd - 'deny = %pV' is overlaps "
                                           "with another 'deny' rule", i + 1, fr_box_ipaddr(deny[i]));
                        goto fail;
                }
 
                /*
                 *      Insert the rule into the trie.
                 */
                if (fr_trie_insert_by_key(trie, &deny[i].addr, deny[i].prefix, FR_BIO_NETWORK_DENY) < 0) {
                        fr_strerror_printf("Failed adding 'deny = %pV' to filtering rules", fr_box_ipaddr(deny[i]));
                        return NULL;
                }
        }
 
        return trie;
}