[PATCH 5.4 091/152] netfilter: xt_hashlimit: reduce hashlimit_mutex scope for htable_put()

Greg Kroah-Hartman
2020-03-03T17:57:15Z

From: Cong Wang <xiyou.wangcong@gmail.com>

commit c4a3922d2d20c710f827d3a115ee338e8d0467df upstream.

It is unnecessary to hold hashlimit_mutex for htable_destroy()
as it is already removed from the global hashtable and its
refcount is already zero.

Also, switch hinfo->use to refcount_t so that we don't have
to hold the mutex until it reaches zero in htable_put().

Reported-and-tested-by: syzbot+adf6c6c2be1c3a718121@syzkaller.appspotmail.com
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/netfilter/xt_hashlimit.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -36,6 +36,7 @@
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/mutex.h>
#include <linux/kernel.h>
+#include <linux/refcount.h>
#include <uapi/linux/netfilter/xt_hashlimit.h>

#define XT_HASHLIMIT_ALL (XT_HASHLIMIT_HASH_DIP | XT_HASHLIMIT_HASH_DPT | \
@@ -114,7 +115,7 @@ struct dsthash_ent {

struct xt_hashlimit_htable {
struct hlist_node node; /* global list of all htables */
- int use;
+ refcount_t use;
u_int8_t family;
bool rnd_initialized;

@@ -315,7 +316,7 @@ static int htable_create(struct net *net
for (i = 0; i < hinfo->cfg.size; i++)
INIT_HLIST_HEAD(&hinfo->hash[i]);

- hinfo->use = 1;
+ refcount_set(&hinfo->use, 1);
hinfo->count = 0;
hinfo->family = family;
hinfo->rnd_initialized = false;
@@ -434,7 +435,7 @@ static struct xt_hashlimit_htable *htabl
hlist_for_each_entry(hinfo, &hashlimit_net->htables, node) {
if (!strcmp(name, hinfo->name) &&
hinfo->family == family) {
- hinfo->use++;
+ refcount_inc(&hinfo->use);
return hinfo;
}
}
@@ -443,12 +444,11 @@ static struct xt_hashlimit_htable *htabl

static void htable_put(struct xt_hashlimit_htable *hinfo)
{
- mutex_lock(&hashlimit_mutex);
- if (--hinfo->use == 0) {
+ if (refcount_dec_and_mutex_lock(&hinfo->use, &hashlimit_mutex)) {
hlist_del(&hinfo->node);
+ mutex_unlock(&hashlimit_mutex);
htable_destroy(hinfo);
}
- mutex_unlock(&hashlimit_mutex);
}

/* The algorithm used is the Simple Token Bucket Filter (TBF)