mirrors/linux-stable
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git synced 2024-09-26 04:16:39 +00:00
Code Issues Releases Wiki Activity

netfilter: conntrack: sanitize table size default settings

Browse source 
conntrack has two distinct table size settings:
nf_conntrack_max and nf_conntrack_buckets.

The former limits how many conntrack objects are allowed to exist
in each namespace.

The second sets the size of the hashtable.

As all entries are inserted twice (once for original direction, once for
reply), there should be at least twice as many buckets in the table than
the maximum number of conntrack objects that can exist at the same time.

Change the default multiplier to 1 and increase the chosen bucket sizes.
This results in the same nf_conntrack_max settings as before but reduces
the average bucket list length.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2021-08-26 15:54:19 +02:00 committed by Pablo Neira Ayuso
parent e3245a7b7b
commit d532bcd0b2
2 changed files with 21 additions and 20 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

13
Documentation/networking/nf_conntrack-sysctl.rst
View file

@ -17,9 +17,8 @@ nf_conntrack_acct - BOOLEAN
nf_conntrack_buckets - INTEGER
Size of hash table. If not specified as parameter during module
loading, the default size is calculated by dividing total memory
by 16384 to determine the number of buckets but the hash table will
never have fewer than 32 and limited to 16384 buckets. For systems
with more than 4GB of memory it will be 65536 buckets.
by 16384 to determine the number of buckets. The hash table will
never have fewer than 1024 and never more than 262144 buckets.
This sysctl is only writeable in the initial net namespace.
nf_conntrack_checksum - BOOLEAN
@ -100,8 +99,12 @@ nf_conntrack_log_invalid - INTEGER
Log invalid packets of a type specified by value.
nf_conntrack_max - INTEGER
Size of connection tracking table. Default value is
nf_conntrack_buckets value * 4.
Maximum number of allowed connection tracking entries. This value is set
to nf_conntrack_buckets by default.
Note that connection tracking entries are added to the table twice -- once
for the original direction and once for the reply direction (i.e., with
the reversed address). This means that with default settings a maxed-out
table will have a average hash chain length of 2, not 1.
nf_conntrack_tcp_be_liberal - BOOLEAN
- 0 - disabled (default)

28
net/netfilter/nf_conntrack_core.c
View file

@ -2594,26 +2594,24 @@ int nf_conntrack_init_start(void)
spin_lock_init(&nf_conntrack_locks[i]);
if (!nf_conntrack_htable_size) {
/* Idea from tcp.c: use 1/16384 of memory.
* On i386: 32MB machine has 512 buckets.
* >= 1GB machines have 16384 buckets.
* >= 4GB machines have 65536 buckets.
*/
nf_conntrack_htable_size
= (((nr_pages << PAGE_SHIFT) / 16384)
/ sizeof(struct hlist_head));
if (nr_pages > (4 * (1024 * 1024 * 1024 / PAGE_SIZE)))
nf_conntrack_htable_size = 65536;
if (BITS_PER_LONG >= 64 &&
nr_pages > (4 * (1024 * 1024 * 1024 / PAGE_SIZE)))
nf_conntrack_htable_size = 262144;
else if (nr_pages > (1024 * 1024 * 1024 / PAGE_SIZE))
nf_conntrack_htable_size = 16384;
if (nf_conntrack_htable_size < 32)
nf_conntrack_htable_size = 32;
nf_conntrack_htable_size = 65536;
/* Use a max. factor of four by default to get the same max as
* with the old struct list_heads. When a table size is given
* we use the old value of 8 to avoid reducing the max.
* entries. */
max_factor = 4;
if (nf_conntrack_htable_size < 1024)
nf_conntrack_htable_size = 1024;
/* Use a max. factor of one by default to keep the average
* hash chain length at 2 entries. Each entry has to be added
* twice (once for original direction, once for reply).
* When a table size is given we use the old value of 8 to
* avoid implicit reduction of the max entries setting.
*/
max_factor = 1;
}
nf_conntrack_hash = nf_ct_alloc_hashtable(&nf_conntrack_htable_size, 1);