netfilter: nfnetlink: add RCU in nfnetlink_rcv_msg()

Goal of this patch is to permit nfnetlink providers not mandate
nfnl_mutex being held while nfnetlink_rcv_msg() calls them.

If struct nfnl_callback contains a non NULL call_rcu(), then
nfnetlink_rcv_msg() will use it instead of call() field, holding
rcu_read_lock instead of nfnl_mutex

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Florian Westphal <fw@strlen.de>
CC: Eric Leblond <eric@regit.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 30 insertions, 10 deletions

diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index b4a4532823e8..1905976b5135 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -37,7 +37,7 @@ MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NETFILTER);
 
 static char __initdata nfversion[] = "0.30";
 
-static const struct nfnetlink_subsystem *subsys_table[NFNL_SUBSYS_COUNT];
+static const struct nfnetlink_subsystem __rcu *subsys_table[NFNL_SUBSYS_COUNT];
 static DEFINE_MUTEX(nfnl_mutex);
 
 void nfnl_lock(void)
@@ -59,7 +59,7 @@ int nfnetlink_subsys_register(const struct nfnetlink_subsystem *n)
                 nfnl_unlock();
                 return -EBUSY;
         }
-        subsys_table[n->subsys_id] = n;
+        rcu_assign_pointer(subsys_table[n->subsys_id], n);
         nfnl_unlock();
 
         return 0;
@@ -71,7 +71,7 @@ int nfnetlink_subsys_unregister(const struct nfnetlink_subsystem *n)
         nfnl_lock();
         subsys_table[n->subsys_id] = NULL;
         nfnl_unlock();
-
+        synchronize_rcu();
         return 0;
 }
 EXPORT_SYMBOL_GPL(nfnetlink_subsys_unregister);
@@ -83,7 +83,7 @@ static inline const struct nfnetlink_subsystem *nfnetlink_get_subsys(u_int16_t t
         if (subsys_id >= NFNL_SUBSYS_COUNT)
                 return NULL;
 
-        return subsys_table[subsys_id];
+        return rcu_dereference(subsys_table[subsys_id]);
 }
 
 static inline const struct nfnl_callback *
@@ -139,21 +139,27 @@ static int nfnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 
         type = nlh->nlmsg_type;
 replay:
+        rcu_read_lock();
         ss = nfnetlink_get_subsys(type);
         if (!ss) {
 #ifdef CONFIG_MODULES
-                nfnl_unlock();
+                rcu_read_unlock();
                 request_module("nfnetlink-subsys-%d", NFNL_SUBSYS_ID(type));
-                nfnl_lock();
+                rcu_read_lock();
                 ss = nfnetlink_get_subsys(type);
                 if (!ss)
 #endif
+                {
+                        rcu_read_unlock();
                         return -EINVAL;
+                }
         }
 
         nc = nfnetlink_find_client(type, ss);
-        if (!nc)
+        if (!nc) {
+                rcu_read_unlock();
                 return -EINVAL;
+        }
 
         {
                 int min_len = NLMSG_SPACE(sizeof(struct nfgenmsg));
@@ -167,7 +173,23 @@ replay:
                 if (err < 0)
                         return err;
 
-                err = nc->call(net->nfnl, skb, nlh, (const struct nlattr **)cda);
+                if (nc->call_rcu) {
+                        err = nc->call_rcu(net->nfnl, skb, nlh,
+                                           (const struct nlattr **)cda);
+                        rcu_read_unlock();
+                } else {
+                        rcu_read_unlock();
+                        nfnl_lock();
+                        if (rcu_dereference_protected(
+                                        subsys_table[NFNL_SUBSYS_ID(type)],
+                                        lockdep_is_held(&nfnl_mutex)) != ss ||
+                            nfnetlink_find_client(type, ss) != nc)
+                                err = -EAGAIN;
+                        else
+                                err = nc->call(net->nfnl, skb, nlh,
+                                                   (const struct nlattr **)cda);
+                        nfnl_unlock();
+                }
                 if (err == -EAGAIN)
                         goto replay;
                 return err;
@@ -176,9 +198,7 @@ replay:
 
 static void nfnetlink_rcv(struct sk_buff *skb)
 {
-        nfnl_lock();
         netlink_rcv_skb(skb, &nfnetlink_rcv_msg);
-        nfnl_unlock();
 }
 
 static int __net_init nfnetlink_net_init(struct net *net)