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Fix handling of large DHCP expiry values.

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They would overflow a signed 32-bit time_t on 32 bit architectures. This
was taken care of, but a compiler optimisation makes this behave
erratically. This could be resolved by adding a -fwrapv flag, but
instead we can check the value before adding the current timestamp to
it.

In the lease file values are still wrong though:

  option dhcp-rebinding-time -644245096;

PR:		218980
Reported by:	Bob Eager
MFC after:	2 weeks
This commit is contained in:
n_hibma 2017-05-07 19:59:37 +00:00
parent ca682b7f08
commit 1260ccd59c
1 changed files with 21 additions and 19 deletions
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40
sbin/dhclient/dhclient.c
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@ -108,7 +108,11 @@ struct pidfh *pidfile;
*/
#define ASSERT_STATE(state_is, state_shouldbe) {}
#define TIME_MAX 2147483647
/*
* We need to check that the expiry, renewal and rebind times are not beyond
* the end of time (~2038 when a 32-bit time_t is being used).
*/
#define TIME_MAX ((((time_t) 1 << (sizeof(time_t) * CHAR_BIT - 2)) - 1) * 2 + 1)
int log_priority;
int no_daemon;
@ -766,15 +770,17 @@ dhcpack(struct packet *packet)
else
ip->client->new->expiry = default_lease_time;
/* A number that looks negative here is really just very large,
because the lease expiry offset is unsigned. */
if (ip->client->new->expiry < 0)
ip->client->new->expiry = TIME_MAX;
because the lease expiry offset is unsigned. Also make sure that
the addition of cur_time below does not overflow (a 32 bit) time_t. */
if (ip->client->new->expiry < 0 ||
ip->client->new->expiry > TIME_MAX - cur_time)
ip->client->new->expiry = TIME_MAX - cur_time;
/* XXX should be fixed by resetting the client state */
if (ip->client->new->expiry < 60)
ip->client->new->expiry = 60;
/* Unless overridden in the config, take the server-provided renewal
* time if there is one; otherwise figure it out according to the spec.
* time if there is one. Otherwise figure it out according to the spec.
* Also make sure the renewal time does not exceed the expiry time.
*/
if (ip->client->config->default_actions[DHO_DHCP_RENEWAL_TIME] ==
@ -786,7 +792,8 @@ dhcpack(struct packet *packet)
ip->client->new->options[DHO_DHCP_RENEWAL_TIME].data);
else
ip->client->new->renewal = ip->client->new->expiry / 2;
if (ip->client->new->renewal > ip->client->new->expiry / 2)
if (ip->client->new->renewal < 0 ||
ip->client->new->renewal > ip->client->new->expiry / 2)
ip->client->new->renewal = ip->client->new->expiry / 2;
/* Same deal with the rebind time. */
@ -798,20 +805,15 @@ dhcpack(struct packet *packet)
ip->client->new->rebind = getULong(
ip->client->new->options[DHO_DHCP_REBINDING_TIME].data);
else
ip->client->new->rebind = ip->client->new->renewal * 7 / 4;
if (ip->client->new->rebind > ip->client->new->renewal * 7 / 4)
ip->client->new->rebind = ip->client->new->renewal * 7 / 4;
ip->client->new->rebind = ip->client->new->renewal / 4 * 7;
if (ip->client->new->rebind < 0 ||
ip->client->new->rebind > ip->client->new->renewal / 4 * 7)
ip->client->new->rebind = ip->client->new->renewal / 4 * 7;
ip->client->new->expiry += cur_time;
/* Lease lengths can never be negative. */
if (ip->client->new->expiry < cur_time)
ip->client->new->expiry = TIME_MAX;
ip->client->new->renewal += cur_time;
if (ip->client->new->renewal < cur_time)
ip->client->new->renewal = TIME_MAX;
ip->client->new->rebind += cur_time;
if (ip->client->new->rebind < cur_time)
ip->client->new->rebind = TIME_MAX;
/* Convert the time offsets into seconds-since-the-epoch */
ip->client->new->expiry += cur_time;
ip->client->new->renewal += cur_time;
ip->client->new->rebind += cur_time;
bind_lease(ip);
}