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hostip: enforce a maximum DNS cache size independent of timeout value

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To reduce the damage an application can cause if using -1 or other
ridiculous timeout values and letting the cache live long times.

The maximum number of entries in the DNS cache is now totally
arbitrarily and hard-coded set to 29999.

Closes #11084
This commit is contained in:
Daniel Stenberg 2023-05-08 11:11:36 +02:00
parent f62557276a
commit 9ed7d56e04
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GPG key ID: 5CC908FDB71E12C2
2 changed files with 42 additions and 13 deletions
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43
lib/hostip.c
View file

@ -85,6 +85,8 @@
#define MAX_HOSTCACHE_LEN (255 + 7) /* max FQDN + colon + port number + zero */
#define MAX_DNS_CACHE_SIZE 29999
/*
* hostip.c explained
* ==================
@ -198,6 +200,7 @@ create_hostcache_id(const char *name,
struct hostcache_prune_data {
time_t now;
int cache_timeout;
int oldest; /* oldest time in cache not pruned */
};
/*
@ -210,28 +213,39 @@ struct hostcache_prune_data {
static int
hostcache_timestamp_remove(void *datap, void *hc)
{
struct hostcache_prune_data *data =
struct hostcache_prune_data *prune =
(struct hostcache_prune_data *) datap;
struct Curl_dns_entry *c = (struct Curl_dns_entry *) hc;
return (0 != c->timestamp)
&& (data->now - c->timestamp >= data->cache_timeout);
if(c->timestamp) {
/* age in seconds */
time_t age = prune->now - c->timestamp;
if(age >= prune->cache_timeout)
return TRUE;
if(age > prune->oldest)
prune->oldest = (int)age;
}
return FALSE;
}
/*
* Prune the DNS cache. This assumes that a lock has already been taken.
* Returns the 'age' of the oldest still kept entry.
*/
static void
static int
hostcache_prune(struct Curl_hash *hostcache, int cache_timeout, time_t now)
{
struct hostcache_prune_data user;
user.cache_timeout = cache_timeout;
user.now = now;
user.oldest = 0;
Curl_hash_clean_with_criterium(hostcache,
(void *) &user,
hostcache_timestamp_remove);
return user.oldest;
}
/*
@ -241,10 +255,11 @@ hostcache_prune(struct Curl_hash *hostcache, int cache_timeout, time_t now)
void Curl_hostcache_prune(struct Curl_easy *data)
{
time_t now;
/* the timeout may be set -1 (forever) */
int timeout = data->set.dns_cache_timeout;
if((data->set.dns_cache_timeout == -1) || !data->dns.hostcache)
/* cache forever means never prune, and NULL hostcache means
we can't do it */
if(!data->dns.hostcache)
/* NULL hostcache means we can't do it */
return;
if(data->share)
@ -252,10 +267,15 @@ void Curl_hostcache_prune(struct Curl_easy *data)
time(&now);
/* Remove outdated and unused entries from the hostcache */
hostcache_prune(data->dns.hostcache,
data->set.dns_cache_timeout,
now);
do {
/* Remove outdated and unused entries from the hostcache */
int oldest = hostcache_prune(data->dns.hostcache, timeout, now);
timeout = oldest;
/* if the cache size is still too big, use the oldest age as new
prune limit */
} while(timeout && (data->dns.hostcache->size > MAX_DNS_CACHE_SIZE));
if(data->share)
Curl_share_unlock(data, CURL_LOCK_DATA_DNS);
@ -298,6 +318,7 @@ static struct Curl_dns_entry *fetch_addr(struct Curl_easy *data,
time(&user.now);
user.cache_timeout = data->set.dns_cache_timeout;
user.oldest = 0;
if(hostcache_timestamp_remove(&user, dns)) {
infof(data, "Hostname in DNS cache was stale, zapped");