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netfilter: conntrack: make max chain length random

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Similar to commit 67d6d681e1
("ipv4: make exception cache less predictible"):

Use a random drop length to make it harder to detect when entries were
hashed to same bucket list.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2021-09-08 14:28:35 +02:00 committed by Pablo Neira Ayuso
parent 310e2d43c3
commit c9c3b6811f
1 changed files with 11 additions and 6 deletions
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17
net/netfilter/nf_conntrack_core.c
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@ -77,7 +77,8 @@ static __read_mostly bool nf_conntrack_locks_all;
#define GC_SCAN_INTERVAL (120u * HZ)
#define GC_SCAN_MAX_DURATION msecs_to_jiffies(10)
#define MAX_CHAINLEN 64u
#define MIN_CHAINLEN 8u
#define MAX_CHAINLEN (32u - MIN_CHAINLEN)
static struct conntrack_gc_work conntrack_gc_work;
@ -842,6 +843,7 @@ nf_conntrack_hash_check_insert(struct nf_conn *ct)
unsigned int hash, reply_hash;
struct nf_conntrack_tuple_hash *h;
struct hlist_nulls_node *n;
unsigned int max_chainlen;
unsigned int chainlen = 0;
unsigned int sequence;
int err = -EEXIST;
@ -857,13 +859,15 @@ nf_conntrack_hash_check_insert(struct nf_conn *ct)
&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
} while (nf_conntrack_double_lock(net, hash, reply_hash, sequence));
max_chainlen = MIN_CHAINLEN + prandom_u32_max(MAX_CHAINLEN);
/* See if there's one in the list already, including reverse */
hlist_nulls_for_each_entry(h, n, &nf_conntrack_hash[hash], hnnode) {
if (nf_ct_key_equal(h, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple,
zone, net))
goto out;
if (chainlen++ > MAX_CHAINLEN)
if (chainlen++ > max_chainlen)
goto chaintoolong;
}
@ -873,7 +877,7 @@ nf_conntrack_hash_check_insert(struct nf_conn *ct)
if (nf_ct_key_equal(h, &ct->tuplehash[IP_CT_DIR_REPLY].tuple,
zone, net))
goto out;
if (chainlen++ > MAX_CHAINLEN)
if (chainlen++ > max_chainlen)
goto chaintoolong;
}
@ -1103,8 +1107,8 @@ drop:
int
__nf_conntrack_confirm(struct sk_buff *skb)
{
unsigned int chainlen = 0, sequence, max_chainlen;
const struct nf_conntrack_zone *zone;
unsigned int chainlen = 0, sequence;
unsigned int hash, reply_hash;
struct nf_conntrack_tuple_hash *h;
struct nf_conn *ct;
@ -1168,6 +1172,7 @@ __nf_conntrack_confirm(struct sk_buff *skb)
goto dying;
}
max_chainlen = MIN_CHAINLEN + prandom_u32_max(MAX_CHAINLEN);
/* See if there's one in the list already, including reverse:
NAT could have grabbed it without realizing, since we're
not in the hash. If there is, we lost race. */
@ -1175,7 +1180,7 @@ __nf_conntrack_confirm(struct sk_buff *skb)
if (nf_ct_key_equal(h, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple,
zone, net))
goto out;
if (chainlen++ > MAX_CHAINLEN)
if (chainlen++ > max_chainlen)
goto chaintoolong;
}
@ -1184,7 +1189,7 @@ __nf_conntrack_confirm(struct sk_buff *skb)
if (nf_ct_key_equal(h, &ct->tuplehash[IP_CT_DIR_REPLY].tuple,
zone, net))
goto out;
if (chainlen++ > MAX_CHAINLEN) {
if (chainlen++ > max_chainlen) {
chaintoolong:
nf_ct_add_to_dying_list(ct);
NF_CT_STAT_INC(net, chaintoolong);