[PATCH AUTOSEL 6.18] netfilter: xt_multiport: validate range encoding in checkentry

[Sasha Levin]

From: Ren Wei <n05ec@xxxxxxxxxx>

[ Upstream commit ff64c5bfef12461df8450e0f50bb693b5269c720 ]

ports_match_v1() treats any non-zero pflags entry as the start of a
port range and unconditionally consumes the next ports[] element as
the range end.

The checkentry path currently validates protocol, flags and count, but
it does not validate the range encoding itself. As a result, malformed
rules can mark the last slot as a range start or place two range starts
back to back, leaving ports_match_v1() to step past the last valid
ports[] element while interpreting the rule.

Reject malformed multiport v1 rules in checkentry by validating that
each range start has a following element and that the following element
is not itself marked as another range start.

Fixes: a89ecb6a2ef7 ("[NETFILTER]: x_tables: unify IPv4/IPv6 multiport match")
Reported-by: Yifan Wu <yifanwucs@xxxxxxxxx>
Reported-by: Juefei Pu <tomapufckgml@xxxxxxxxx>
Co-developed-by: Yuan Tan <yuantan098@xxxxxxxxx>
Signed-off-by: Yuan Tan <yuantan098@xxxxxxxxx>
Suggested-by: Xin Liu <bird@xxxxxxxxxx>
Tested-by: Yuhang Zheng <z1652074432@xxxxxxxxx>
Signed-off-by: Ren Wei <n05ec@xxxxxxxxxx>
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---

LLM Generated explanations, may be completely bogus:

Error: Failed to generate final synthesis

 net/netfilter/xt_multiport.c | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/xt_multiport.c b/net/netfilter/xt_multiport.c
index 44a00f5acde8a..a1691ff405d3c 100644
--- a/net/netfilter/xt_multiport.c
+++ b/net/netfilter/xt_multiport.c
@@ -105,6 +105,28 @@ multiport_mt(const struct sk_buff *skb, struct xt_action_param *par)
 	return ports_match_v1(multiinfo, ntohs(pptr[0]), ntohs(pptr[1]));
 }
 
+static bool
+multiport_valid_ranges(const struct xt_multiport_v1 *multiinfo)
+{
+	unsigned int i;
+
+	for (i = 0; i < multiinfo->count; i++) {
+		if (!multiinfo->pflags[i])
+			continue;
+
+		if (++i >= multiinfo->count)
+			return false;
+
+		if (multiinfo->pflags[i])
+			return false;
+
+		if (multiinfo->ports[i - 1] > multiinfo->ports[i])
+			return false;
+	}
+
+	return true;
+}
+
 static inline bool
 check(u_int16_t proto,
       u_int8_t ip_invflags,
@@ -127,8 +149,10 @@ static int multiport_mt_check(const struct xt_mtchk_param *par)
 	const struct ipt_ip *ip = par->entryinfo;
 	const struct xt_multiport_v1 *multiinfo = par->matchinfo;
 
-	return check(ip->proto, ip->invflags, multiinfo->flags,
-		     multiinfo->count) ? 0 : -EINVAL;
+	if (!check(ip->proto, ip->invflags, multiinfo->flags, multiinfo->count))
+		return -EINVAL;
+
+	return multiport_valid_ranges(multiinfo) ? 0 : -EINVAL;
 }
 
 static int multiport_mt6_check(const struct xt_mtchk_param *par)
@@ -136,8 +160,10 @@ 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;
 
-	return check(ip->proto, ip->invflags, multiinfo->flags,
-		     multiinfo->count) ? 0 : -EINVAL;
+	if (!check(ip->proto, ip->invflags, multiinfo->flags, multiinfo->count))
+		return -EINVAL;
+
+	return multiport_valid_ranges(multiinfo) ? 0 : -EINVAL;
 }
 
 static struct xt_match multiport_mt_reg[] __read_mostly = {
-- 
2.53.0