netdev - [PATCH net-next 3/9] netfilter: bridge: check len before accessing more nh data

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Message-Id: <20230308193033.13965-4-fw@strlen.de>
Date:   Wed,  8 Mar 2023 20:30:27 +0100
From:   Florian Westphal <fw@...len.de>
To:     <netdev@...r.kernel.org>
Cc:     Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        <netfilter-devel@...r.kernel.org>, Xin Long <lucien.xin@...il.com>,
        Simon Horman <simon.horman@...igine.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Aaron Conole <aconole@...hat.com>
Subject: [PATCH net-next 3/9] netfilter: bridge: check len before accessing more nh data

From: Xin Long <lucien.xin@...il.com>

In the while loop of br_nf_check_hbh_len(), similar to ip6_parse_tlv(),
before accessing 'nh[off + 1]', it should add a check 'len < 2'; and
before parsing IPV6_TLV_JUMBO, it should add a check 'optlen > len',
in case of overflows.

Signed-off-by: Xin Long <lucien.xin@...il.com>
Reviewed-by: Simon Horman <simon.horman@...igine.com>
Acked-by: Nikolay Aleksandrov <razor@...ckwall.org>
Reviewed-by: Aaron Conole <aconole@...hat.com>
Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/bridge/br_netfilter_ipv6.c | 45 +++++++++++++++-------------------
 1 file changed, 20 insertions(+), 25 deletions(-)

diff --git a/net/bridge/br_netfilter_ipv6.c b/net/bridge/br_netfilter_ipv6.c
index afd1c718b683..8be3c5c8b925 100644
--- a/net/bridge/br_netfilter_ipv6.c
+++ b/net/bridge/br_netfilter_ipv6.c
@@ -50,54 +50,49 @@ static int br_nf_check_hbh_len(struct sk_buff *skb)
 	u32 pkt_len;
 
 	if (!pskb_may_pull(skb, off + 8))
-		goto bad;
+		return -1;
 	nh = (unsigned char *)(ipv6_hdr(skb) + 1);
 	len = (nh[1] + 1) << 3;
 
 	if (!pskb_may_pull(skb, off + len))
-		goto bad;
+		return -1;
 	nh = skb_network_header(skb);
 
 	off += 2;
 	len -= 2;
-
 	while (len > 0) {
-		int optlen = nh[off + 1] + 2;
-
-		switch (nh[off]) {
-		case IPV6_TLV_PAD1:
-			optlen = 1;
-			break;
+		int optlen;
 
-		case IPV6_TLV_PADN:
-			break;
+		if (nh[off] == IPV6_TLV_PAD1) {
+			off++;
+			len--;
+			continue;
+		}
+		if (len < 2)
+			return -1;
+		optlen = nh[off + 1] + 2;
+		if (optlen > len)
+			return -1;
 
-		case IPV6_TLV_JUMBO:
+		if (nh[off] == IPV6_TLV_JUMBO) {
 			if (nh[off + 1] != 4 || (off & 3) != 2)
-				goto bad;
+				return -1;
 			pkt_len = ntohl(*(__be32 *)(nh + off + 2));
 			if (pkt_len <= IPV6_MAXPLEN ||
 			    ipv6_hdr(skb)->payload_len)
-				goto bad;
+				return -1;
 			if (pkt_len > skb->len - sizeof(struct ipv6hdr))
-				goto bad;
+				return -1;
 			if (pskb_trim_rcsum(skb,
 					    pkt_len + sizeof(struct ipv6hdr)))
-				goto bad;
+				return -1;
 			nh = skb_network_header(skb);
-			break;
-		default:
-			if (optlen > len)
-				goto bad;
-			break;
 		}
 		off += optlen;
 		len -= optlen;
 	}
-	if (len == 0)
-		return 0;
-bad:
-	return -1;
+
+	return len ? -1 : 0;
 }
 
 int br_validate_ipv6(struct net *net, struct sk_buff *skb)
-- 
2.39.2