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Don't compute each checksum twice when adding dummy headers (-u, -T, -s, -S options) 

g_ntohs() & friends may be (are ?) macros and may (will ?) eval args more than once ...


svn path=/trunk/; revision=36272
This commit is contained in:
Bill Meier 2011-03-23 00:43:55 +00:00
parent 263a3b3d10
commit 31b01ae88e
1 changed files with 31 additions and 15 deletions
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46
text2pcap.c
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@ -423,7 +423,8 @@ in_checksum (void *buf, unsigned long count)
while (sum>>16)
sum = (sum & 0xffff) + (sum >> 16);
return g_htons(~sum);
sum = ~sum;
return g_htons(sum);
}
/* The CRC32C code is taken from draft-ietf-tsvwg-sctpcsum-01.txt.
@ -605,16 +606,22 @@ write_current_packet (void)
/* Write UDP header */
if (hdr_udp) {
guint16 x16;
HDR_UDP.source_port = g_htons(hdr_src_port);
HDR_UDP.dest_port = g_htons(hdr_dest_port);
HDR_UDP.length = g_htons(proto_length);
/* Note: g_ntohs()/g_htons() macro arg may be eval'd twice so calc value before invoking macro */
HDR_UDP.checksum = 0;
u = g_ntohs(in_checksum(&pseudoh, sizeof(pseudoh))) +
g_ntohs(in_checksum(&HDR_UDP, sizeof(HDR_UDP))) +
g_ntohs(in_checksum(packet_buf, curr_offset));
HDR_UDP.checksum = g_htons((u & 0xffff) + (u>>16));
if (HDR_UDP.checksum == 0) /* differenciate between 'none' and 0 */
x16 = in_checksum(&pseudoh, sizeof(pseudoh));
u = g_ntohs(x16);
x16 = in_checksum(&HDR_UDP, sizeof(HDR_UDP));
u += g_ntohs(x16);
x16 = in_checksum(packet_buf, curr_offset);
u += g_ntohs(x16);
x16 = (u & 0xffff) + (u>>16);
HDR_UDP.checksum = g_htons(x16);
if (HDR_UDP.checksum == 0) /* differentiate between 'none' and 0 */
HDR_UDP.checksum = g_htons(1);
fwrite(&HDR_UDP, sizeof(HDR_UDP), 1, output_file);
@ -622,18 +629,24 @@ write_current_packet (void)
/* Write TCP header */
if (hdr_tcp) {
guint16 x16;
HDR_TCP.source_port = g_htons(hdr_src_port);
HDR_TCP.dest_port = g_htons(hdr_dest_port);
/* HDR_TCP.seq_num already correct */
HDR_TCP.window = g_htons(0x2000);
/* Note: g_ntohs()/g_htons() macro arg may be eval'd twice so calc value before invoking macro */
HDR_TCP.checksum = 0;
u = g_ntohs(in_checksum(&pseudoh, sizeof(pseudoh))) +
g_ntohs(in_checksum(&HDR_TCP, sizeof(HDR_TCP))) +
g_ntohs(in_checksum(packet_buf, curr_offset));
HDR_TCP.checksum = g_htons((u & 0xffff) + (u>>16));
if (HDR_TCP.checksum == 0) /* differenciate between 'none' and 0 */
HDR_TCP.checksum = g_htons(1);
x16 = in_checksum(&pseudoh, sizeof(pseudoh));
u = g_ntohs(x16);
x16 = in_checksum(&HDR_TCP, sizeof(HDR_TCP));
u += g_ntohs(x16);
x16 = in_checksum(packet_buf, curr_offset);
u += g_ntohs(x16);
x16 = (u & 0xffff) + (u>>16);
HDR_TCP.checksum = g_htons(x16);
if (HDR_TCP.checksum == 0) /* differentiate between 'none' and 0 */
HDR_TCP.checksum = g_htons(1);
fwrite(&HDR_TCP, sizeof(HDR_TCP), 1, output_file);
}
@ -655,6 +668,7 @@ write_current_packet (void)
/* Write SCTP header */
if (hdr_sctp) {
guint32 x32;
HDR_SCTP.src_port = g_htons(hdr_sctp_src);
HDR_SCTP.dest_port = g_htons(hdr_sctp_dest);
HDR_SCTP.tag = g_htonl(hdr_sctp_tag);
@ -662,7 +676,9 @@ write_current_packet (void)
HDR_SCTP.checksum = crc32c((guint8 *)&HDR_SCTP, sizeof(HDR_SCTP), ~0L);
if (hdr_data_chunk)
HDR_SCTP.checksum = crc32c((guint8 *)&HDR_DATA_CHUNK, sizeof(HDR_DATA_CHUNK), HDR_SCTP.checksum);
HDR_SCTP.checksum = g_htonl(finalize_crc32c(crc32c(packet_buf, curr_offset, HDR_SCTP.checksum)));
/* Note: g_ntohl() macro arg may be eval'd twice so calc value before invoking macro */
x32 = finalize_crc32c(crc32c(packet_buf, curr_offset, HDR_SCTP.checksum));
HDR_SCTP.checksum = g_htonl(x32);
fwrite(&HDR_SCTP, sizeof(HDR_SCTP), 1, output_file);
}
@ -684,8 +700,8 @@ write_current_packet (void)
fprintf(stderr, "Wrote packet of %lu bytes at %u\n", curr_offset, g_ntohl(HDR_TCP.seq_num));
num_packets_written ++;
}
HDR_TCP.seq_num = g_htonl(g_ntohl(HDR_TCP.seq_num) + curr_offset);
HDR_TCP.seq_num = g_ntohl(HDR_TCP.seq_num) + curr_offset;
HDR_TCP.seq_num = g_htonl(HDR_TCP.seq_num);
packet_start += curr_offset;
curr_offset = 0;