[PATCH nf 1/2] ipvs: validate cport in received sync records

Local templates have cport 0 and IP_VS_CONN_F_NO_CPORT clear, so
ip_vs_conn_in_get() cannot match them. A template received over the
unauthenticated sync protocol with a nonzero cport can reach the
protocol state machine. Before template state validation, this
could cause out-of-bounds reads, crashes and kernel data leaks.

Ordinary records with cport 0 and IP_VS_CONN_F_NO_CPORT clear, or
with a nonzero cport and IP_VS_CONN_F_NO_CPORT set, create connections
that incoming lookups cannot match. The latter also keeps the
cport-zero fallback in ip_vs_conn_in_get() enabled.

Reject all three cases. Continue accepting ordinary connections
with cport 0 and IP_VS_CONN_F_NO_CPORT. The companion patch
"ipvs: filter some flags received in the backup server" rejects
template records carrying IP_VS_CONN_F_NO_CPORT.

Fixes: 87375ab47cd0 ("[IPVS]: ip_vs_ftp breaks connections using persistence")
Cc: stable@vger.kernel.org
Suggested-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Axel Mierczuk <redacted>
---
 net/netfilter/ipvs/ip_vs_sync.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/net/netfilter/ipvs/ip_vs_sync.c b/net/netfilter/ipvs/ip_vs_sync.c
index 5383aeafb0ae..3998e9a0a391 100644
--- a/net/netfilter/ipvs/ip_vs_sync.c
+++ b/net/netfilter/ipvs/ip_vs_sync.c

@@ -848,6 +848,25 @@ static void ip_vs_proc_conn(struct netns_ipvs *ipvs, struct ip_vs_conn_param *pa
 	struct ip_vs_dest *dest;
 	struct ip_vs_conn *cp;
 
+	/* Templates require cport 0. Ordinary connections require
+	 * NO_CPORT exactly when cport is 0.
+	 */
+	if (flags & IP_VS_CONN_F_TEMPLATE) {
+		if (param->cport) {
+			IP_VS_DBG(2, "BACKUP, template with cport dropped\n");
+			kfree(param->pe_data);
+			return;
+		}
+	} else if (!param->cport && !(flags & IP_VS_CONN_F_NO_CPORT)) {
+		IP_VS_DBG(2, "BACKUP, conn without cport dropped\n");
+		kfree(param->pe_data);
+		return;
+	} else if (param->cport && (flags & IP_VS_CONN_F_NO_CPORT)) {
+		IP_VS_DBG(2, "BACKUP, conn with cport and NO_CPORT dropped\n");
+		kfree(param->pe_data);
+		return;
+	}
+
 	if (!(flags & IP_VS_CONN_F_TEMPLATE)) {
 		cp = ip_vs_conn_in_get(param);
 		if (cp && ((cp->dport != dport) ||

-- 
2.43.0