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netfilter: conntrack: avoid useless indirection during conntrack destruction 

nf_ct_put() results in a usesless indirection:

nf_ct_put -> nf_conntrack_put -> nf_conntrack_destroy -> rcu readlock +
indirect call of ct_hooks->destroy().

There are two _put helpers:
nf_ct_put and nf_conntrack_put.  The latter is what should be used in
code that MUST NOT cause a linker dependency on the conntrack module
(e.g. calls from core network stack).

Everyone else should call nf_ct_put() instead.

A followup patch will convert a few nf_conntrack_put() calls to
nf_ct_put(), in particular from modules that already have a conntrack
dependency such as act_ct or even nf_conntrack itself.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2022-01-07 05:03:25 +01:00 committed by Pablo Neira Ayuso
parent 285c8a7a58
commit 6ae7989c9a
3 changed files with 14 additions and 8 deletions
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2
include/linux/netfilter/nf_conntrack_common.h
View File

@ -29,6 +29,8 @@ struct nf_conntrack {
};
void nf_conntrack_destroy(struct nf_conntrack *nfct);
/* like nf_ct_put, but without module dependency on nf_conntrack */
static inline void nf_conntrack_put(struct nf_conntrack *nfct)
{
if (nfct && refcount_dec_and_test(&nfct->use))

8
include/net/netfilter/nf_conntrack.h
View File

@ -76,6 +76,8 @@ struct nf_conn {
* Hint, SKB address this struct and refcnt via skb->_nfct and
* helpers nf_conntrack_get() and nf_conntrack_put().
* Helper nf_ct_put() equals nf_conntrack_put() by dec refcnt,
* except that the latter uses internal indirection and does not
* result in a conntrack module dependency.
* beware nf_ct_get() is different and don't inc refcnt.
*/
struct nf_conntrack ct_general;
@ -170,11 +172,13 @@ nf_ct_get(const struct sk_buff *skb, enum ip_conntrack_info *ctinfo)
return (struct nf_conn *)(nfct & NFCT_PTRMASK);
}
void nf_ct_destroy(struct nf_conntrack *nfct);
/* decrement reference count on a conntrack */
static inline void nf_ct_put(struct nf_conn *ct)
{
WARN_ON(!ct);
nf_conntrack_put(&ct->ct_general);
if (ct && refcount_dec_and_test(&ct->ct_general.use))
nf_ct_destroy(&ct->ct_general);
}
/* Protocol module loading */

12
net/netfilter/nf_conntrack_core.c
View File

@ -558,7 +558,7 @@ static void nf_ct_del_from_dying_or_unconfirmed_list(struct nf_conn *ct)
#define NFCT_ALIGN(len) (((len) + NFCT_INFOMASK) & ~NFCT_INFOMASK)
/* Released via destroy_conntrack() */
/* Released via nf_ct_destroy() */
struct nf_conn *nf_ct_tmpl_alloc(struct net *net,
const struct nf_conntrack_zone *zone,
gfp_t flags)
@ -612,12 +612,11 @@ static void destroy_gre_conntrack(struct nf_conn *ct)
#endif
}
static void
destroy_conntrack(struct nf_conntrack *nfct)
void nf_ct_destroy(struct nf_conntrack *nfct)
{
struct nf_conn *ct = (struct nf_conn *)nfct;
pr_debug("destroy_conntrack(%p)\n", ct);
pr_debug("%s(%p)\n", __func__, ct);
WARN_ON(refcount_read(&nfct->use) != 0);
if (unlikely(nf_ct_is_template(ct))) {
@ -643,9 +642,10 @@ destroy_conntrack(struct nf_conntrack *nfct)
if (ct->master)
nf_ct_put(ct->master);
pr_debug("destroy_conntrack: returning ct=%p to slab\n", ct);
pr_debug("%s: returning ct=%p to slab\n", __func__, ct);
nf_conntrack_free(ct);
}
EXPORT_SYMBOL(nf_ct_destroy);
static void nf_ct_delete_from_lists(struct nf_conn *ct)
{
@ -2771,7 +2771,7 @@ err_cachep:
static const struct nf_ct_hook nf_conntrack_hook = {
.update = nf_conntrack_update,
.destroy = destroy_conntrack,
.destroy = nf_ct_destroy,
.get_tuple_skb = nf_conntrack_get_tuple_skb,
.attach = nf_conntrack_attach,
};