From fadeddfbb2aa38a980dd959b5ec1ffba7afd43cb Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 15 Apr 2024 20:02:34 +0200 Subject: Adding upstream version 1.0.18. Signed-off-by: Daniel Baumann --- src/daemon/frame.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 66 insertions(+) create mode 100644 src/daemon/frame.c (limited to 'src/daemon/frame.c') diff --git a/src/daemon/frame.c b/src/daemon/frame.c new file mode 100644 index 0000000..adc4629 --- /dev/null +++ b/src/daemon/frame.c @@ -0,0 +1,66 @@ +/* -*- mode: c; c-file-style: "openbsd" -*- */ +/* + * Copyright (c) 2009 Vincent Bernat + * + * Permission to use, copy, modify, and/or distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ + +#include "lldpd.h" + +/** + * Compute the checksum as 16-bit word. + */ +u_int16_t +frame_checksum(const u_char *cp, int len, int cisco) +{ + unsigned int sum = 0, v = 0; + int oddbyte = 0; + + while ((len -= 2) >= 0) { + sum += *cp++ << 8; + sum += *cp++; + } + if ((oddbyte = len & 1) != 0) v = *cp; + + /* The remaining byte seems to be handled oddly by Cisco. From function + * dissect_cdp() in wireshark. 2014/6/14,zhengy@yealink.com: + * + * CDP doesn't adhere to RFC 1071 section 2. (B). It incorrectly assumes + * checksums are calculated on a big endian platform, therefore i.s.o. + * padding odd sized data with a zero byte _at the end_ it sets the last + * big endian _word_ to contain the last network _octet_. This byteswap + * has to be done on the last octet of network data before feeding it to + * the Internet checksum routine. + * CDP checksumming code has a bug in the addition of this last _word_ + * as a signed number into the long word intermediate checksum. When + * reducing this long to word size checksum an off-by-one error can be + * made. This off-by-one error is compensated for in the last _word_ of + * the network data. + */ + if (oddbyte) { + if (cisco) { + if (v & 0x80) { + sum += 0xff << 8; + sum += v - 1; + } else { + sum += v; + } + } else { + sum += v << 8; + } + } + + sum = (sum >> 16) + (sum & 0xffff); + sum += sum >> 16; + return (0xffff & ~sum); +} -- cgit v1.2.3