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ntpd: improve postponed hostname resolution

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Run the namelookup from the main loop so a misspelled first ntp server
name does not block everything forever.

This fixes the following situation which would block forever:
  $ sudo ./busybox ntpd -dn -p foobar  -p pool.ntp.org
  ntpd: bad address 'foobar'
  ntpd: bad address 'foobar'
  ntpd: bad address 'foobar'
  ...

New behavior:
  ntpd: bad address 'foobar'
  ntpd: sending query to 137.190.2.4
  ntpd: reply from 137.190.2.4: offset:-1.009775 delay:0.175550 status:0x24 strat:1 refid:0x00535047 rootdelay:0.000000 reach:0x01
  ntpd: sending query to 137.190.2.4
  ntpd: reply from 137.190.2.4: offset:-1.009605 delay:0.175461 status:0x24 strat:1 refid:0x00535047 rootdelay:0.000000 reach:0x03
  ntpd: sending query to 137.190.2.4
  ntpd: reply from 137.190.2.4: offset:-1.005327 delay:0.167027 status:0x24 strat:1 refid:0x00535047 rootdelay:0.000000 reach:0x07
  ntpd: sending query to 137.190.2.4
  ntpd: bad address 'foobar'
  ntpd: reply from 137.190.2.4: offset:-1.046349 delay:0.248705 status:0x24 strat:1 refid:0x00535047 rootdelay:0.000000 reach:0x0f

This patch is based on Kaarle Ritvanens work.
http://lists.busybox.net/pipermail/busybox/2016-May/084197.html

function                                             old     new   delta
ntpd_main                                           1061    1079     +18
ntp_init                                             556     560      +4
resolve_peer_hostname                                 81      75      -6
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/1 up/down: 22/-6)              Total: 16 bytes

Signed-off-by: Kaarle Ritvanen <kaarle.ritvanen@datakunkku.fi>
Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Natanael Copa 2017-01-06 16:18:45 +01:00 committed by Denys Vlasenko
parent e6add210b2
commit b62ea34afe
1 changed files with 34 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

73
networking/ntpd.c
View File

@ -155,6 +155,7 @@
#define RETRY_INTERVAL 32 /* on send/recv error, retry in N secs (need to be power of 2) */
#define NOREPLY_INTERVAL 512 /* sent, but got no reply: cap next query by this many seconds */
#define RESPONSE_INTERVAL 16 /* wait for reply up to N secs */
#define HOSTNAME_INTERVAL 5 /* hostname lookup failed. Wait N secs for next try */
/* Step threshold (sec). std ntpd uses 0.128.
*/
@ -790,28 +791,20 @@ reset_peer_stats(peer_t *p, double offset)
VERB6 bb_error_msg("%s->lastpkt_recv_time=%f", p->p_dotted, p->lastpkt_recv_time);
}
static void
resolve_peer_hostname(peer_t *p, int loop_on_fail)
static len_and_sockaddr*
resolve_peer_hostname(peer_t *p)
{
len_and_sockaddr *lsa;
again:
lsa = host2sockaddr(p->p_hostname, 123);
if (!lsa) {
/* error message already emitted by host2sockaddr() */
if (!loop_on_fail)
return;
//FIXME: do this to avoid infinite looping on typo in a hostname?
//well... in which case, what is a good value for loop_on_fail?
//if (--loop_on_fail == 0)
// xfunc_die();
sleep(5);
goto again;
len_and_sockaddr *lsa = host2sockaddr(p->p_hostname, 123);
if (lsa) {
free(p->p_lsa);
free(p->p_dotted);
p->p_lsa = lsa;
p->p_dotted = xmalloc_sockaddr2dotted_noport(&lsa->u.sa);
} else {
/* error message is emitted by host2sockaddr() */
set_next(p, HOSTNAME_INTERVAL);
}
free(p->p_lsa);
free(p->p_dotted);
p->p_lsa = lsa;
p->p_dotted = xmalloc_sockaddr2dotted_noport(&lsa->u.sa);
return lsa;
}
static void
@ -822,28 +815,28 @@ add_peers(const char *s)
p = xzalloc(sizeof(*p) + strlen(s));
strcpy(p->p_hostname, s);
resolve_peer_hostname(p, /*loop_on_fail=*/ 1);
p->p_fd = -1;
p->p_xmt_msg.m_status = MODE_CLIENT | (NTP_VERSION << 3);
p->next_action_time = G.cur_time; /* = set_next(p, 0); */
reset_peer_stats(p, STEP_THRESHOLD);
/* Names like N.<country2chars>.pool.ntp.org are randomly resolved
* to a pool of machines. Sometimes different N's resolve to the same IP.
* It is not useful to have two peers with same IP. We skip duplicates.
*/
for (item = G.ntp_peers; item != NULL; item = item->link) {
peer_t *pp = (peer_t *) item->data;
if (strcmp(p->p_dotted, pp->p_dotted) == 0) {
bb_error_msg("duplicate peer %s (%s)", s, p->p_dotted);
free(p->p_lsa);
free(p->p_dotted);
free(p);
return;
if (resolve_peer_hostname(p)) {
for (item = G.ntp_peers; item != NULL; item = item->link) {
peer_t *pp = (peer_t *) item->data;
if (pp->p_dotted && strcmp(p->p_dotted, pp->p_dotted) == 0) {
bb_error_msg("duplicate peer %s (%s)", s, p->p_dotted);
free(p->p_lsa);
free(p->p_dotted);
free(p);
return;
}
}
}
p->p_fd = -1;
p->p_xmt_msg.m_status = MODE_CLIENT | (NTP_VERSION << 3);
p->next_action_time = G.cur_time; /* = set_next(p, 0); */
reset_peer_stats(p, STEP_THRESHOLD);
llist_add_to(&G.ntp_peers, p);
G.peer_cnt++;
}
@ -871,6 +864,11 @@ do_sendto(int fd,
static void
send_query_to_peer(peer_t *p)
{
if (!p->p_lsa) {
if (!resolve_peer_hostname(p))
return;
}
/* Why do we need to bind()?
* See what happens when we don't bind:
*
@ -2238,7 +2236,7 @@ static NOINLINE void ntp_init(char **argv)
IF_FEATURE_NTPD_SERVER("I:") /* compat */
"d" /* compat */
"46aAbgL", /* compat, ignored */
&peers,&G.script_name,
&peers, &G.script_name,
#if ENABLE_FEATURE_NTPD_SERVER
&G.if_name,
#endif
@ -2263,9 +2261,6 @@ static NOINLINE void ntp_init(char **argv)
if (opts & OPT_N)
setpriority(PRIO_PROCESS, 0, -15);
/* add_peers() calls can retry DNS resolution (possibly forever).
* Daemonize before them, or else boot can stall forever.
*/
if (!(opts & OPT_n)) {
bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO, argv);
logmode = LOGMODE_NONE;
@ -2400,7 +2395,7 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
/* What if don't see it because it changed its IP? */
if (p->reachable_bits == 0)
resolve_peer_hostname(p, /*loop_on_fail=*/ 0);
resolve_peer_hostname(p);
set_next(p, timeout);
}