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      1 /* SPDX-License-Identifier: BSD-2-Clause */
      2 /*
      3  * dhcpcd: BPF arp and bootp filtering
      4  * Copyright (c) 2006-2025 Roy Marples <roy (at) marples.name>
      5  * All rights reserved
      6 
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     26  * SUCH DAMAGE.
     27  */
     28 
     29 #ifndef BPF_HEADER
     30 #define BPF_HEADER
     31 
     32 #define	BPF_EOF			0x01U
     33 #define	BPF_PARTIALCSUM		0x02U
     34 #define	BPF_BCAST		0x04U
     35 
     36 /*
     37  * Even though we program the BPF filter should we trust it?
     38  * On Linux at least there is a window between opening the socket,
     39  * binding the interface and setting the filter where we receive data.
     40  * This data is NOT checked OR flushed and IS returned when reading.
     41  * We have no way of flushing it other than reading these packets!
     42  * But we don't know if they passed the filter or not ..... so we need
     43  * to validate each and every packet that comes through ourselves as well.
     44  * Even if Linux does fix this sorry state, who is to say other kernels
     45  * don't have bugs causing a similar effect?
     46  *
     47  * As such, let's strive to keep the filters just for pattern matching
     48  * to avoid waking dhcpcd up.
     49  *
     50  * If you want to be notified of any packet failing the BPF filter,
     51  * define BPF_DEBUG below.
     52  */
     53 //#define	BPF_DEBUG
     54 
     55 #include "dhcpcd.h"
     56 
     57 struct bpf {
     58 	const struct interface *bpf_ifp;
     59 	int bpf_fd;
     60 	unsigned int bpf_flags;
     61 	void *bpf_buffer;
     62 	size_t bpf_size;
     63 	size_t bpf_len;
     64 	size_t bpf_pos;
     65 };
     66 
     67 extern const char *bpf_name;
     68 size_t bpf_frame_header_len(const struct interface *);
     69 void *bpf_frame_header_src(const struct interface *, void *, size_t *);
     70 void *bpf_frame_header_dst(const struct interface *, void *, size_t *);
     71 int bpf_frame_bcast(const struct interface *, const void *);
     72 struct bpf * bpf_open(const struct interface *,
     73     int (*)(const struct bpf *, const struct in_addr *),
     74     const struct in_addr *);
     75 void bpf_close(struct bpf *);
     76 int bpf_attach(int, void *, unsigned int);
     77 ssize_t bpf_send(const struct bpf *, uint16_t, const void *, size_t);
     78 ssize_t bpf_read(struct bpf *, void *, size_t);
     79 int bpf_arp(const struct bpf *, const struct in_addr *);
     80 int bpf_bootp(const struct bpf *, const struct in_addr *);
     81 #endif
     82