netdev - [PATCH] net: Move specific fragmented packet to slow

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Message-ID: <20250417092953.8275-1-huajianyang@asrmicro.com>
Date: Thu, 17 Apr 2025 17:29:53 +0800
From: Huajian Yang <huajianyang@...micro.com>
To: <pablo@...filter.org>, <fw@...len.de>
CC: <kadlec@...filter.org>, <razor@...ckwall.org>, <idosch@...dia.com>,
        <davem@...emloft.net>, <dsahern@...nel.org>, <edumazet@...gle.com>,
        <kuba@...nel.org>, <pabeni@...hat.com>, <horms@...nel.org>,
        <netfilter-devel@...r.kernel.org>, <coreteam@...filter.org>,
        <bridge@...ts.linux.dev>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Huajian Yang <huajianyang@...micro.com>
Subject: [PATCH] net: Move specific fragmented packet to slow_path instead of dropping it

The config NF_CONNTRACK_BRIDGE will change the bridge forwarding for
fragmented packets.

The original bridge does not know that it is a fragmented packet and
forwards it directly, after NF_CONNTRACK_BRIDGE is enabled, function
nf_br_ip_fragment and br_ip6_fragment will check the headroom.

In original br_forward, insufficient headroom of skb may indeed exist,
but there's still a way to save the skb in the device driver after
dev_queue_xmit.So droping the skb will change the original bridge
forwarding in some cases.

Signed-off-by: Huajian Yang <huajianyang@...micro.com>
---
 net/bridge/netfilter/nf_conntrack_bridge.c | 12 ++++++------
 net/ipv6/netfilter.c                       | 12 ++++++------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/net/bridge/netfilter/nf_conntrack_bridge.c b/net/bridge/netfilter/nf_conntrack_bridge.c
index 816bb0fde718..6482de4d8750 100644
--- a/net/bridge/netfilter/nf_conntrack_bridge.c
+++ b/net/bridge/netfilter/nf_conntrack_bridge.c
@@ -60,19 +60,19 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk,
 		struct ip_fraglist_iter iter;
 		struct sk_buff *frag;
 
-		if (first_len - hlen > mtu ||
-		    skb_headroom(skb) < ll_rs)
+		if (first_len - hlen > mtu)
 			goto blackhole;
 
-		if (skb_cloned(skb))
+		if (skb_cloned(skb) ||
+		    skb_headroom(skb) < ll_rs)
 			goto slow_path;
 
 		skb_walk_frags(skb, frag) {
-			if (frag->len > mtu ||
-			    skb_headroom(frag) < hlen + ll_rs)
+			if (frag->len > mtu)
 				goto blackhole;
 
-			if (skb_shared(frag))
+			if (skb_shared(frag) ||
+			    skb_headroom(frag) < hlen + ll_rs)
 				goto slow_path;
 		}
 
diff --git a/net/ipv6/netfilter.c b/net/ipv6/netfilter.c
index 581ce055bf52..4541836ee3da 100644
--- a/net/ipv6/netfilter.c
+++ b/net/ipv6/netfilter.c
@@ -164,20 +164,20 @@ int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 		struct ip6_fraglist_iter iter;
 		struct sk_buff *frag2;
 
-		if (first_len - hlen > mtu ||
-		    skb_headroom(skb) < (hroom + sizeof(struct frag_hdr)))
+		if (first_len - hlen > mtu)
 			goto blackhole;
 
-		if (skb_cloned(skb))
+		if (skb_cloned(skb) ||
+		    skb_headroom(skb) < (hroom + sizeof(struct frag_hdr)))
 			goto slow_path;
 
 		skb_walk_frags(skb, frag2) {
-			if (frag2->len > mtu ||
-			    skb_headroom(frag2) < (hlen + hroom + sizeof(struct frag_hdr)))
+			if (frag2->len > mtu)
 				goto blackhole;
 
 			/* Partially cloned skb? */
-			if (skb_shared(frag2))
+			if (skb_shared(frag2) ||
+			    skb_headroom(frag2) < (hlen + hroom + sizeof(struct frag_hdr)))
 				goto slow_path;
 		}
 
-- 
2.48.1