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dhclient: Keep two clocks

Browse source 
Until July 2024, dhclient kept track of time as seconds-since-epoch as
a time_t.  This was a problem because (a) we wanted sub-second timeouts
and (b) timeouts didn't always do the right thing if the system clock
changed.

Switching to using CLOCK_MONOTONIC and struct timespec fixed those
issues but introduced a new problem: CLOCK_MONOTONIC values were being
intepreted as seconds-since-epoch and written to the dhclient.leases
file, causing confusion with DHCP leases expiring in early 1970.

Attempt to compromise between these by keeping track of both times;
any type within dhclient which is a time_t now refers to seconds past
the epoch, while any struct timespec value is a CLOCK_MONOTONIC time.

PR:	283256
Reviewed by:	dch
Fixes:	f0a38976b01e ("dhclient: Use clock_gettime() instead of time()")
Sponsored by:	Amazon
Differential Revision:	https://reviews.freebsd.org/D49720

(cherry picked from commit 43d19e6a4c42ade0f276ceca18a09e2e3829fce4)
This commit is contained in:
Colin Percival 2025-04-08 15:50:01 -07:00
parent 6ea58552f0
commit d41725ab43
3 changed files with 33 additions and 35 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

50
sbin/dhclient/dhclient.c
View file

@ -90,8 +90,8 @@
cap_channel_t *capsyslog;
time_t cur_time;
struct timespec time_now;
time_t cur_time; /* Seconds since epoch. */
struct timespec time_now; /* CLOCK_MONOTONIC. */
static time_t default_lease_time = 43200; /* 12 hours... */
const char *path_dhclient_conf = _PATH_DHCLIENT_CONF;
@ -450,7 +450,7 @@ main(int argc, char *argv[])
tzset();
clock_gettime(CLOCK_MONOTONIC, &time_now);
cur_time = time_now.tv_sec;
cur_time = time(NULL);
inaddr_broadcast.s_addr = INADDR_BROADCAST;
inaddr_any.s_addr = INADDR_ANY;
@ -1030,13 +1030,13 @@ dhcpoffer(struct packet *packet)
struct client_lease *lease, *lp;
int i;
struct timespec arp_timeout_needed;
struct timespec stop_selecting = { .tv_sec = 0, .tv_nsec = 0 };
time_now.tv_sec = cur_time;
time_now.tv_nsec = 0;
time_t stop_selecting;
struct timespec stop_time;
const char *name = packet->options[DHO_DHCP_MESSAGE_TYPE].len ?
"DHCPOFFER" : "BOOTREPLY";
clock_gettime(CLOCK_MONOTONIC, &time_now);
/* If we're not receptive to an offer right now, or if the offer
has an unrecognizable transaction id, then just drop it. */
if (ip->client->state != S_SELECTING ||
@ -1095,7 +1095,7 @@ dhcpoffer(struct packet *packet)
arp_timeout_needed = arp_timeout;
/* Figure out when we're supposed to stop selecting. */
stop_selecting.tv_sec =
stop_selecting =
ip->client->first_sending + ip->client->config->select_interval;
/* If this is the lease we asked for, put it at the head of the
@ -1116,7 +1116,7 @@ dhcpoffer(struct packet *packet)
timespecadd(&time_now, &arp_timeout_needed, &interm_struct);
if (ip->client->offered_leases &&
timespeccmp(&interm_struct, &stop_selecting, >))
interm_struct.tv_sec >= stop_selecting)
arp_timeout_needed = zero_timespec;
/* Put the lease at the end of the list. */
@ -1131,27 +1131,21 @@ dhcpoffer(struct packet *packet)
}
}
/* If we're supposed to stop selecting before we've had time
to wait for the ARPREPLY, add some delay to wait for
the ARPREPLY. */
struct timespec time_left;
timespecsub(&stop_selecting, &time_now, &time_left);
/*
* Wait until stop_selecting seconds past the epoch, or until
* arp_timeout_needed past now, whichever is longer. Note that
* the first case only occurs if select-timeout is set to nonzero
* in dhclient.conf.
*/
struct timespec time_left =
{.tv_sec = stop_selecting - cur_time, .tv_nsec = 0};
if (timespeccmp(&time_left, &arp_timeout_needed, <)) {
timespecadd(&time_now, &arp_timeout_needed, &stop_selecting);
}
/* If the selecting interval has expired, go immediately to
state_selecting(). Otherwise, time out into
state_selecting at the select interval. */
if (timespeccmp(&stop_selecting, &zero_timespec, <=))
state_selecting(ip);
else {
add_timeout_timespec(stop_selecting, state_selecting, ip);
cancel_timeout(send_discover, ip);
timespecadd(&time_now, &arp_timeout_needed, &stop_time);
} else {
timespecadd(&time_now, &time_left, &stop_time);
}
add_timeout_timespec(stop_time, state_selecting, ip);
cancel_timeout(send_discover, ip);
}
/* Allocate a client_lease structure and initialize it from the parameters

4
sbin/dhclient/dhcpd.h
View file

@ -362,8 +362,8 @@ char *piaddr(struct iaddr);
extern cap_channel_t *capsyslog;
extern const char *path_dhclient_conf;
extern char *path_dhclient_db;
extern struct timespec time_now;
extern time_t cur_time;
extern struct timespec time_now; /* CLOCK_MONOTONIC */
extern time_t cur_time; /* Seconds since epoch */
extern int log_priority;
extern int log_perror;

14
sbin/dhclient/dispatch.c
View file

@ -160,8 +160,8 @@ dispatch(void)
struct protocol *l;
struct pollfd *fds;
struct timespec howlong;
time_now.tv_sec = cur_time;
time_now.tv_nsec = 0;
clock_gettime(CLOCK_MONOTONIC, &time_now);
for (l = protocols; l; l = l->next)
nfds++;
@ -225,7 +225,7 @@ another:
if (count == -1) {
if (errno == EAGAIN || errno == EINTR) {
clock_gettime(CLOCK_MONOTONIC, &time_now);
cur_time = time_now.tv_sec;
cur_time = time(NULL);
continue;
} else
error("poll: %m");
@ -233,7 +233,7 @@ another:
/* Get the current time... */
clock_gettime(CLOCK_MONOTONIC, &time_now);
cur_time = time_now.tv_sec;
cur_time = time(NULL);
i = 0;
for (l = protocols; l; l = l->next) {
@ -366,7 +366,11 @@ active:
void
add_timeout(time_t when_s, void (*where)(void *), void *what)
{
struct timespec when = { .tv_sec = when_s, .tv_nsec = 0 };
struct timespec when;
cur_time = time(NULL);
clock_gettime(CLOCK_MONOTONIC, &when);
when.tv_sec += when_s - cur_time;
add_timeout_timespec(when, where, what);
}