diff options
Diffstat (limited to 'csum.h')
| -rw-r--r-- | csum.h | 179 |
1 files changed, 179 insertions, 0 deletions
@@ -0,0 +1,179 @@ +/* + * netsniff-ng - the packet sniffing beast + * Copyright 2010 Emmanuel Roullit. + * Subject to the GPL, version 2. + */ + +#ifndef CSUM_H +#define CSUM_H + +#include <netinet/in.h> +#include <netinet/ip.h> + +#include "built_in.h" + +static inline unsigned short csum(unsigned short *buf, int nwords) +{ + unsigned long sum; + + for (sum = 0; nwords > 0; nwords--) + sum += *buf++; + sum = (sum >> 16) + (sum & 0xffff); + sum += (sum >> 16); + + return ~sum; +} + +static inline uint16_t calc_csum(void *addr, size_t len, int ccsum) +{ + return csum(addr, len >> 1); +} + +static inline uint16_t csum_expected(uint16_t sum, uint16_t computed_sum) +{ + uint32_t shouldbe; + + shouldbe = sum; + shouldbe += ntohs(computed_sum); + shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16); + shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16); + + return shouldbe; +} + +/* Taken and modified from tcpdump, Copyright belongs to them! */ + +struct cksum_vec { + const u8 *ptr; + int len; +}; + +#define ADDCARRY(x) \ + do { if ((x) > 65535) \ + (x) -= 65535; \ + } while (0) + +#define REDUCE \ + do { \ + l_util.l = sum; \ + sum = l_util.s[0] + l_util.s[1]; \ + ADDCARRY(sum); \ + } while (0) + +static inline u16 __in_cksum(const struct cksum_vec *vec, int veclen) +{ + const u16 *w; + int sum = 0, mlen = 0; + int byte_swapped = 0; + union { + u8 c[2]; + u16 s; + } s_util; + union { + u16 s[2]; + u32 l; + } l_util; + + for (; veclen != 0; vec++, veclen--) { + if (vec->len == 0) + continue; + + w = (const u16 *) (void *) vec->ptr; + + if (mlen == -1) { + s_util.c[1] = *(const u8 *) w; + sum += s_util.s; + w = (const u16 *) (void *) ((const u8 *) w + 1); + mlen = vec->len - 1; + } else + mlen = vec->len; + + if ((1 & (unsigned long) w) && (mlen > 0)) { + REDUCE; + sum <<= 8; + s_util.c[0] = *(const u8 *) w; + w = (const u16 *) (void *) ((const u8 *) w + 1); + mlen--; + byte_swapped = 1; + } + + while ((mlen -= 32) >= 0) { + sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; + sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7]; + sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11]; + sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15]; + w += 16; + } + + mlen += 32; + + while ((mlen -= 8) >= 0) { + sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; + w += 4; + } + + mlen += 8; + + if (mlen == 0 && byte_swapped == 0) + continue; + + REDUCE; + + while ((mlen -= 2) >= 0) { + sum += *w++; + } + + if (byte_swapped) { + REDUCE; + sum <<= 8; + byte_swapped = 0; + + if (mlen == -1) { + s_util.c[1] = *(const u8 *) w; + sum += s_util.s; + mlen = 0; + } else + mlen = -1; + } else if (mlen == -1) + s_util.c[0] = *(const u8 *) w; + } + + if (mlen == -1) { + s_util.c[1] = 0; + sum += s_util.s; + } + + REDUCE; + + return (~sum & 0xffff); +} + +static inline u16 p4_csum(const struct ip *ip, const u8 *data, u16 len, + u8 next_proto) +{ + struct cksum_vec vec[2]; + struct pseudo_hdr { + u32 src; + u32 dst; + u8 mbz; + u8 proto; + u16 len; + } ph; + + memset(&ph, 0, sizeof(ph)); + ph.len = htons(len); + ph.mbz = 0; + ph.proto = next_proto; + ph.src = ip->ip_src.s_addr; + ph.dst = ip->ip_dst.s_addr; + + vec[0].ptr = (const u8 *) (void *) &ph; + vec[0].len = sizeof(ph); + + vec[1].ptr = data; + vec[1].len = len; + + return __in_cksum(vec, 2); +} + +#endif /* CSUM_H */ |