[PATCH nf] netfilter: x_tables: require IP6T_F_PROTO when matching protocol

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

Several check() functions validate the protocol field value but do not
require IP6T_F_PROTO. A crafted ip6tables rule can set the field to TCP
or UDP while leaving the protocol matching flag clear.

Reject rules without IP6T_F_PROTO so the match/target is invoked only
for the protocols it supports.

In the TPROXY target, this allows to reach a WARN in packet path.

Fixes: 6ad7889327a5e ("tproxy: added IPv6 support to the TPROXY target")
Link: https://patch.msgid.link/cover.1786968834.git.zhilinz@nebusec.ai/
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
Florian mentioned xt_l2tp is also missing this, but xt_multiport also
needs it. I could not find any other user of .proto which does not
validate IP6T_F_PROTO in IPv6.

 net/netfilter/xt_TPROXY.c    |  3 ++-
 net/netfilter/xt_ecn.c       |  1 +
 net/netfilter/xt_l2tp.c      | 20 ++++++++++++--------
 net/netfilter/xt_multiport.c |  3 +++
 4 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/net/netfilter/xt_TPROXY.c b/net/netfilter/xt_TPROXY.c
index 5f60e7298a1e..13a94c9d06c0 100644
--- a/net/netfilter/xt_TPROXY.c
+++ b/net/netfilter/xt_TPROXY.c
@@ -179,7 +179,8 @@ static int tproxy_tg6_check(const struct xt_tgchk_param *par)
 	if (err)
 		return err;
 
-	if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP) &&
+	if ((i->flags & IP6T_F_PROTO) &&
+	    (i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP) &&
 	    !(i->invflags & IP6T_INV_PROTO))
 		return 0;
 
diff --git a/net/netfilter/xt_ecn.c b/net/netfilter/xt_ecn.c
index a8503f5d26bf..a5c99f00c201 100644
--- a/net/netfilter/xt_ecn.c
+++ b/net/netfilter/xt_ecn.c
@@ -139,6 +139,7 @@ static int ecn_mt_check6(const struct xt_mtchk_param *par)
 		return -EINVAL;
 
 	if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
+	    ip->flags & IP6T_F_PROTO &&
 	    (ip->proto != IPPROTO_TCP || ip->invflags & IP6T_INV_PROTO)) {
 		pr_info_ratelimited("cannot match TCP bits for non-tcp packets\n");
 		return -EINVAL;
diff --git a/net/netfilter/xt_l2tp.c b/net/netfilter/xt_l2tp.c
index a61eb81e9f49..346cbc168009 100644
--- a/net/netfilter/xt_l2tp.c
+++ b/net/netfilter/xt_l2tp.c
@@ -267,14 +267,16 @@ static int l2tp_mt_check4(const struct xt_mtchk_param *par)
 	if (ret != 0)
 		return ret;
 
-	if ((ip->proto != IPPROTO_UDP) &&
-	    (ip->proto != IPPROTO_L2TP)) {
+	if (!(ip->flags & IP6T_F_PROTO) ||
+	    (ip->proto != IPPROTO_UDP &&
+	     ip->proto != IPPROTO_L2TP)) {
 		pr_info_ratelimited("missing protocol rule (udp|l2tpip)\n");
 		return -EINVAL;
 	}
 
-	if ((ip->proto == IPPROTO_L2TP) &&
-	    (info->version == 2)) {
+	if (!(ip->flags & IP6T_F_PROTO) ||
+	    (ip->proto == IPPROTO_L2TP &&
+	     info->version == 2)) {
 		pr_info_ratelimited("v2 doesn't support IP mode\n");
 		return -EINVAL;
 	}
@@ -294,14 +296,16 @@ static int l2tp_mt_check6(const struct xt_mtchk_param *par)
 	if (ret != 0)
 		return ret;
 
-	if ((ip->proto != IPPROTO_UDP) &&
-	    (ip->proto != IPPROTO_L2TP)) {
+	if (!(ip->flags & IP6T_F_PROTO) ||
+	    (ip->proto != IPPROTO_UDP &&
+	     ip->proto != IPPROTO_L2TP)) {
 		pr_info_ratelimited("missing protocol rule (udp|l2tpip)\n");
 		return -EINVAL;
 	}
 
-	if ((ip->proto == IPPROTO_L2TP) &&
-	    (info->version == 2)) {
+	if (!(ip->flags & IP6T_F_PROTO) ||
+	    (ip->proto == IPPROTO_L2TP &&
+	     info->version == 2)) {
 		pr_info_ratelimited("v2 doesn't support IP mode\n");
 		return -EINVAL;
 	}
diff --git a/net/netfilter/xt_multiport.c b/net/netfilter/xt_multiport.c
index bff5f53a9bef..b48c2cbbee62 100644
--- a/net/netfilter/xt_multiport.c
+++ b/net/netfilter/xt_multiport.c
@@ -156,6 +156,9 @@ static int multiport_mt6_check(const struct xt_mtchk_param *par)
 	const struct ip6t_ip6 *ip = par->entryinfo;
 	const struct xt_multiport_v1 *multiinfo = par->matchinfo;
 
+	if (!(ip->flags & IP6T_F_PROTO))
+		return -EINVAL;
+
 	if (!check(ip->proto, ip->invflags, multiinfo->flags, multiinfo->count))
 		return -EINVAL;
 
-- 
2.47.3