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ethermess
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Randomize message ID start

This commit is contained in:
Juhani Krekelä 2019-07-09 16:35:48 +03:00
parent 43540d51bc
commit 541dd28a64
1 changed files with 30 additions and 6 deletions
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36
ethermess.c
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@ -3,6 +3,7 @@
#include <assert.h> #include <assert.h>
#include <err.h> #include <err.h>
#include <errno.h> #include <errno.h>
#include <fcntl.h>
#include <inttypes.h> #include <inttypes.h>
#include <linux/if_packet.h> #include <linux/if_packet.h>
#include <net/ethernet.h> #include <net/ethernet.h>
@ -16,6 +17,7 @@
#include <string.h> #include <string.h>
#include <sys/ioctl.h> #include <sys/ioctl.h>
#include <sys/socket.h> #include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h> #include <sys/types.h>
#include <unistd.h> #include <unistd.h>
@ -33,6 +35,7 @@
bool running = true; bool running = true;
int packet_socket; int packet_socket;
int urandom;
unsigned char own_mac[6]; unsigned char own_mac[6];
unsigned char broadcast_mac[6] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff}; unsigned char broadcast_mac[6] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff};
@ -75,8 +78,11 @@ ssize_t msgid_cache_add(const unsigned char mac[6]) {
// If we are adding into a new slot (instead of overwriting one), // If we are adding into a new slot (instead of overwriting one),
// expand the fill pointer // expand the fill pointer
if (msgid_cache_fill < index) { //
msgid_cache_fill++; // + 1 because msgid_cache_fill of N means that cache slots [0, N-1]
// are in use
if (msgid_cache_fill < index + 1) {
msgid_cache_fill = index + 1;
} }
memcpy(msgid_cache[index].other_mac, mac, sizeof(msgid_cache[index].other_mac)); memcpy(msgid_cache[index].other_mac, mac, sizeof(msgid_cache[index].other_mac));
@ -86,6 +92,15 @@ ssize_t msgid_cache_add(const unsigned char mac[6]) {
return index; return index;
} }
unsigned char random_byte(void) {
unsigned char randomness;
errno = 0;
if (read(urandom, &randomness, 1) != 1) {
err(1, "read");
}
return randomness;
}
char hexify(int nybble) { char hexify(int nybble) {
assert(0 <= nybble && nybble <= 16); assert(0 <= nybble && nybble <= 16);
return "0123456789abcdef"[nybble]; return "0123456789abcdef"[nybble];
@ -199,9 +214,8 @@ void send_msgid(const unsigned char destination[6]) {
if (!msgid_cache[cache_index].know_receive) { if (!msgid_cache[cache_index].know_receive) {
// We don't have receive ID stored in the cache // We don't have receive ID stored in the cache
// In that case, start from 0 // In that case, start from a random index
// TODO: Make it random instead msgid_cache[cache_index].next_receive = (random_byte() << 8) | random_byte();
msgid_cache[cache_index].next_receive = 0;
msgid_cache[cache_index].know_receive = true; msgid_cache[cache_index].know_receive = true;
} }
@ -215,6 +229,7 @@ void send_msgid(const unsigned char destination[6]) {
} }
void read_command(void) { void read_command(void) {
errno = 0;
int cmd = getchar(); int cmd = getchar();
if (cmd == EOF) { if (cmd == EOF) {
err(1, "getchar"); err(1, "getchar");
@ -356,7 +371,7 @@ void process_frame(void) {
errno = 0; errno = 0;
ssize_t res = recv(packet_socket, frame, sizeof(frame), 0); ssize_t res = recv(packet_socket, frame, sizeof(frame), 0);
if (res == -1) { if (res == -1) {
errx(1, "recv"); err(1, "recv");
} else if (res < 16) { } else if (res < 16) {
// Frame too short to contain enough information // Frame too short to contain enough information
return; return;
@ -480,6 +495,9 @@ int main(int argc, char **argv) {
const char *interface_name = argv[1]; const char *interface_name = argv[1];
// Open /dev/urandom for getting randomness
urandom = open("/dev/urandom", O_RDONLY);
// Create a packet socket // Create a packet socket
errno = 0; errno = 0;
packet_socket = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL)); packet_socket = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
@ -545,5 +563,11 @@ int main(int argc, char **argv) {
err(1, "fflush"); err(1, "fflush");
} }
// Close urandom
errno = 0;
if (close(urandom) == -1) {
err(1, "close");
}
return 0; return 0;
} }