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Use a helper to ensure xid always changes when we advance it.

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The purpose of the changing xid is to prevent misinterpreting
delayed messages, and the rare chance where it's randomly the
same breaks this sequence-id property.
This commit is contained in:
Nicholas J. Kain 2022-08-28 04:41:11 -04:00
parent 9b8e2facbf
commit 4d739acbdd
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3 changed files with 11 additions and 4 deletions
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2
dhcp.c
View File

@ -413,7 +413,7 @@ static void init_packet(struct dhcpmsg *packet, uint8_t type)
ssize_t send_discover(struct client_state_t *cs)
{
cs->xid = nk_random_u32(&cs->rnd_state);
advance_xid(cs);
struct dhcpmsg packet = {.xid = cs->xid};
init_packet(&packet, DHCPDISCOVER);
if (cs->clientAddr)

7
ndhc.h
View File

@ -86,5 +86,12 @@ void signal_exit(int status);
int get_clientid_string(const char *str, size_t slen);
void print_version(void);
static inline void advance_xid(struct client_state_t *cs) {
uint32_t o = cs->xid;
do {
cs->xid = nk_random_u32(&cs->rnd_state);
} while (cs->xid == o);
}
#endif

6
state.c
View File

@ -53,7 +53,7 @@ static int delay_timeout(struct client_state_t *cs, size_t numpackets)
static void reinit_shared_deconfig(struct client_state_t *cs)
{
nk_random_init(&cs->rnd_state);
cs->xid = nk_random_u32(&cs->rnd_state);
advance_xid(cs);
cs->clientAddr = 0;
cs->num_dhcp_requests = 0;
cs->num_dhcp_renews = 0;
@ -224,7 +224,7 @@ static int extend_packet(struct client_state_t *cs,
clibuf, sizeof clibuf);
log_line("%s: Server is now offering IP %s. Validating...",
client_config.interface, clibuf);
cs->xid = nk_random_u32(&cs->rnd_state);
advance_xid(cs);
return ANP_CHECK_IP;
} else {
log_line("%s: Lease refreshed to %u seconds.",
@ -233,7 +233,7 @@ static int extend_packet(struct client_state_t *cs,
log_line("%s: Failed to create ARP defense socket.",
client_config.interface);
stop_dhcp_listen(cs);
cs->xid = nk_random_u32(&cs->rnd_state);
advance_xid(cs);
return ANP_SUCCESS;
}
} else if (msgtype == DHCPNAK) {