[PATCH net-next 13/15] netfilter: conntrack: call nf_ct_gre_keymap_destroy() if master helper is pptp

[Pablo Neira Ayuso <pablo@netfilter.org>]

For GRE flows, validate that the ct master helper (if any) is pptp
before calling nf_ct_gre_keymap_destroy(), so the helper data area
can be accessed safely. Note that only the pptp helper provides a
.destroy callback.

Fixes: e56894356f60 ("netfilter: conntrack: remove l4proto destroy hook")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nf_conntrack_core.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 91255fd3b35d..4fb3a2d18631 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -562,9 +562,23 @@ static void destroy_gre_conntrack(struct nf_conn *ct)
 {
 #ifdef CONFIG_NF_CT_PROTO_GRE
 	struct nf_conn *master = ct->master;
+	struct nf_conn_help *help;
+
+	if (!master)
+		return;
+
+	help = nfct_help(master);
+	if (help) {
+		struct nf_conntrack_helper *helper;
 
-	if (master)
-		nf_ct_gre_keymap_destroy(master);
+		rcu_read_lock();
+		helper = rcu_dereference(help->helper);
+		/* Only pptp helper has a destroy callback. */
+		if (helper && helper->destroy)
+			nf_ct_gre_keymap_destroy(master);
+
+		rcu_read_unlock();
+	}
 #endif
 }
 
-- 
2.47.3