[RFC v3 nf-next 09/15] netfilter: nfnetlink_cttimeout: use rcu protection in cttimeout_get_timeout

[Florian Westphal <fw@strlen.de>]

I'd like to be able to switch lifetime management of ctnl_timeout
to free-on-zero-refcount.

This isn't possible at the moment because removal of the structures
from the pernet list requires the nfnl mutex and release may happen from
softirq.

Current solution is to prevent this by disallowing policy object removal
if the refcount is > 1 (i.e., policy is still referenced from the ruleset).

Switch traversal to rcu-read-lock as a first step to reduce reliance on
nfnl mutex protection: removal from softirq would require a extra list
spinlock.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nfnetlink_cttimeout.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/net/netfilter/nfnetlink_cttimeout.c b/net/netfilter/nfnetlink_cttimeout.c
index eea486f32971..c9cdc605f486 100644
--- a/net/netfilter/nfnetlink_cttimeout.c
+++ b/net/netfilter/nfnetlink_cttimeout.c
@@ -253,6 +253,7 @@ static int cttimeout_get_timeout(struct sk_buff *skb,
 				 const struct nlattr * const cda[])
 {
 	struct nfct_timeout_pernet *pernet = nfct_timeout_pernet(info->net);
+	struct sk_buff *skb2;
 	int ret = -ENOENT;
 	char *name;
 	struct ctnl_timeout *cur;
@@ -268,31 +269,31 @@ static int cttimeout_get_timeout(struct sk_buff *skb,
 		return -EINVAL;
 	name = nla_data(cda[CTA_TIMEOUT_NAME]);
 
-	list_for_each_entry(cur, &pernet->nfct_timeout_list, head) {
-		struct sk_buff *skb2;
+	skb2 = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
+	if (skb2 == NULL)
+		return -ENOMEM;
 
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(cur, &pernet->nfct_timeout_list, head) {
 		if (strncmp(cur->name, name, CTNL_TIMEOUT_NAME_MAX) != 0)
 			continue;
 
-		skb2 = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
-		if (skb2 == NULL) {
-			ret = -ENOMEM;
-			break;
-		}
-
 		ret = ctnl_timeout_fill_info(skb2, NETLINK_CB(skb).portid,
 					     info->nlh->nlmsg_seq,
 					     NFNL_MSG_TYPE(info->nlh->nlmsg_type),
 					     IPCTNL_MSG_TIMEOUT_NEW, cur);
-		if (ret <= 0) {
-			kfree_skb(skb2);
+		if (ret <= 0)
 			break;
-		}
 
-		ret = nfnetlink_unicast(skb2, info->net, NETLINK_CB(skb).portid);
-		break;
+		rcu_read_unlock();
+
+		return nfnetlink_unicast(skb2, info->net, NETLINK_CB(skb).portid);
 	}
 
+	rcu_read_unlock();
+	kfree_skb(skb2);
+
 	return ret;
 }
 
-- 
2.34.1