netfilter: nfnetlink_cthelper: use {READ,WRITE}_ONCE for accessing helper flags

Conntrack helper flags are accessed from packet and netlink dump path.
Concurrent update of userspace helper flags is not possible, because the
nfnl_mutex in held on updates. These flags are only used by userspace
helpers. Use {READ,WRITE}_ONCE() to access this flags from lockless
paths.

Fixes: 12f7a505331e ("netfilter: add user-space connection tracking helper infrastructure")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 16 insertions, 8 deletions

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index b521b5ebd664..c072a14a306a 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -2213,6 +2213,7 @@ static int nf_confirm_cthelper(struct sk_buff *skb, struct nf_conn *ct,
 {
 	const struct nf_conntrack_helper *helper;
 	const struct nf_conn_help *help;
+	unsigned int helper_flags;
 	int protoff;
 
 	help = nfct_help(ct);
@@ -2223,7 +2224,8 @@ static int nf_confirm_cthelper(struct sk_buff *skb, struct nf_conn *ct,
 	if (!helper)
 		return NF_ACCEPT;
 
-	if (!(helper->flags & NF_CT_HELPER_F_USERSPACE))
+	helper_flags = READ_ONCE(helper->flags);
+	if (!(helper_flags & NF_CT_HELPER_F_USERSPACE))
 		return NF_ACCEPT;
 
 	switch (nf_ct_l3num(ct)) {
diff --git a/net/netfilter/nfnetlink_cthelper.c b/net/netfilter/nfnetlink_cthelper.c
index 34af6840803e..267eac1167f3 100644
--- a/net/netfilter/nfnetlink_cthelper.c
+++ b/net/netfilter/nfnetlink_cthelper.c
@@ -41,8 +41,9 @@ static int
 nfnl_userspace_cthelper(struct sk_buff *skb, unsigned int protoff,
 			struct nf_conn *ct, enum ip_conntrack_info ctinfo)
 {
-	const struct nf_conn_help *help;
 	struct nf_conntrack_helper *helper;
+	const struct nf_conn_help *help;
+	unsigned int helper_flags;
 
 	help = nfct_help(ct);
 	if (help == NULL)
@@ -53,8 +54,10 @@ nfnl_userspace_cthelper(struct sk_buff *skb, unsigned int protoff,
 	if (helper == NULL)
 		return NF_DROP;
 
+	helper_flags = READ_ONCE(helper->flags);
+
 	/* This is a user-space helper not yet configured, skip. */
-	if ((helper->flags &
+	if ((helper_flags &
 	    (NF_CT_HELPER_F_USERSPACE | NF_CT_HELPER_F_CONFIGURED)) ==
 	     NF_CT_HELPER_F_USERSPACE)
 		return NF_ACCEPT;
@@ -404,10 +407,10 @@ nfnl_cthelper_update(const struct nlattr * const tb[],
 
 		switch(status) {
 		case NFCT_HELPER_STATUS_ENABLED:
-			helper->flags |= NF_CT_HELPER_F_CONFIGURED;
+			WRITE_ONCE(helper->flags, helper->flags | NF_CT_HELPER_F_CONFIGURED);
 			break;
 		case NFCT_HELPER_STATUS_DISABLED:
-			helper->flags &= ~NF_CT_HELPER_F_CONFIGURED;
+			WRITE_ONCE(helper->flags, helper->flags & ~NF_CT_HELPER_F_CONFIGURED);
 			break;
 		}
 	}
@@ -529,8 +532,8 @@ static int
 nfnl_cthelper_fill_info(struct sk_buff *skb, u32 portid, u32 seq, u32 type,
 			int event, struct nf_conntrack_helper *helper)
 {
-	struct nlmsghdr *nlh;
 	unsigned int flags = portid ? NLM_F_MULTI : 0;
+	struct nlmsghdr *nlh;
 	int status;
 
 	event = nfnl_msg_type(NFNL_SUBSYS_CTHELPER, event);
@@ -554,7 +557,7 @@ nfnl_cthelper_fill_info(struct sk_buff *skb, u32 portid, u32 seq, u32 type,
 	if (nla_put_be32(skb, NFCTH_PRIV_DATA_LEN, htonl(helper->data_len)))
 		goto nla_put_failure;
 
-	if (helper->flags & NF_CT_HELPER_F_CONFIGURED)
+	if (READ_ONCE(helper->flags) & NF_CT_HELPER_F_CONFIGURED)
 		status = NFCT_HELPER_STATUS_ENABLED;
 	else
 		status = NFCT_HELPER_STATUS_DISABLED;
@@ -575,6 +578,7 @@ static int
 nfnl_cthelper_dump_table(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	struct nf_conntrack_helper *cur, *last;
+	unsigned int helper_flags;
 
 	rcu_read_lock();
 	last = (struct nf_conntrack_helper *)cb->args[1];
@@ -583,8 +587,10 @@ restart:
 		hlist_for_each_entry_rcu(cur,
 				&nf_ct_helper_hash[cb->args[0]], hnode) {
 
+			helper_flags = READ_ONCE(cur->flags);
+
 			/* skip non-userspace conntrack helpers. */
-			if (!(cur->flags & NF_CT_HELPER_F_USERSPACE))
+			if (!(helper_flags & NF_CT_HELPER_F_USERSPACE))
 				continue;
 
 			if (cb->args[1]) {