[PATCH 4.4 019/193] netfilter: xt_RATEEST: acquire xt_rateest_mutex for hash insert

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

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

commit 7dc68e98757a8eccf8ca7a53a29b896f1eef1f76 upstream.

rateest_hash is supposed to be protected by xt_rateest_mutex,
and, as suggested by Eric, lookup and insert should be atomic,
so we should acquire the xt_rateest_mutex once for both.

So introduce a non-locking helper for internal use and keep the
locking one for external.

Reported-by: <syzbot+5cb189720978275e4...@syzkaller.appspotmail.com>
Fixes: 5859034d7eb8 ("[NETFILTER]: x_tables: add RATEEST target")
Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
Reviewed-by: Florian Westphal <f...@strlen.de>
Reviewed-by: Eric Dumazet <eduma...@google.com>
Signed-off-by: Pablo Neira Ayuso <pa...@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 net/netfilter/xt_RATEEST.c |   22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

--- a/net/netfilter/xt_RATEEST.c
+++ b/net/netfilter/xt_RATEEST.c
@@ -40,23 +40,31 @@ static void xt_rateest_hash_insert(struc
        hlist_add_head(&est->list, &rateest_hash[h]);
 }
 
-struct xt_rateest *xt_rateest_lookup(const char *name)
+static struct xt_rateest *__xt_rateest_lookup(const char *name)
 {
        struct xt_rateest *est;
        unsigned int h;
 
        h = xt_rateest_hash(name);
-       mutex_lock(&xt_rateest_mutex);
        hlist_for_each_entry(est, &rateest_hash[h], list) {
                if (strcmp(est->name, name) == 0) {
                        est->refcnt++;
-                       mutex_unlock(&xt_rateest_mutex);
                        return est;
                }
        }
-       mutex_unlock(&xt_rateest_mutex);
+
        return NULL;
 }
+
+struct xt_rateest *xt_rateest_lookup(const char *name)
+{
+       struct xt_rateest *est;
+
+       mutex_lock(&xt_rateest_mutex);
+       est = __xt_rateest_lookup(name);
+       mutex_unlock(&xt_rateest_mutex);
+       return est;
+}
 EXPORT_SYMBOL_GPL(xt_rateest_lookup);
 
 void xt_rateest_put(struct xt_rateest *est)
@@ -104,8 +112,10 @@ static int xt_rateest_tg_checkentry(cons
                rnd_inited = true;
        }
 
-       est = xt_rateest_lookup(info->name);
+       mutex_lock(&xt_rateest_mutex);
+       est = __xt_rateest_lookup(info->name);
        if (est) {
+               mutex_unlock(&xt_rateest_mutex);
                /*
                 * If estimator parameters are specified, they must match the
                 * existing estimator.
@@ -143,11 +153,13 @@ static int xt_rateest_tg_checkentry(cons
 
        info->est = est;
        xt_rateest_hash_insert(est);
+       mutex_unlock(&xt_rateest_mutex);
        return 0;
 
 err2:
        kfree(est);
 err1:
+       mutex_unlock(&xt_rateest_mutex);
        return ret;
 }