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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Lina Wang <lina.wang@mediatek.com>,
        "David S . Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>, edumazet@google.com,
        kuba@kernel.org, pabeni@redhat.com, matthias.bgg@gmail.com,
        ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
        ilias.apalodimas@linaro.org, vasily.averin@linux.dev,
        luiz.von.dentz@intel.com, netdev@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, bpf@vger.kernel.org
Subject: [PATCH AUTOSEL 5.17 14/23] net: fix wrong network header length
Date:   Wed, 18 May 2022 08:26:27 -0400
Message-Id: <20220518122641.342120-14-sashal@kernel.org>
In-Reply-To: <20220518122641.342120-1-sashal@kernel.org>
References: <20220518122641.342120-1-sashal@kernel.org>
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From: Lina Wang <lina.wang@mediatek.com>

[ Upstream commit cf3ab8d4a797960b4be20565abb3bcd227b18a68 ]

When clatd starts with ebpf offloaing, and NETIF_F_GRO_FRAGLIST is enable,
several skbs are gathered in skb_shinfo(skb)->frag_list. The first skb's
ipv6 header will be changed to ipv4 after bpf_skb_proto_6_to_4,
network_header\transport_header\mac_header have been updated as ipv4 acts,
but other skbs in frag_list didnot update anything, just ipv6 packets.

udp_queue_rcv_skb will call skb_segment_list to traverse other skbs in
frag_list and make sure right udp payload is delivered to user space.
Unfortunately, other skbs in frag_list who are still ipv6 packets are
updated like the first skb and will have wrong transport header length.

e.g.before bpf_skb_proto_6_to_4,the first skb and other skbs in frag_list
has the same network_header(24)& transport_header(64), after
bpf_skb_proto_6_to_4, ipv6 protocol has been changed to ipv4, the first
skb's network_header is 44,transport_header is 64, other skbs in frag_list
didnot change.After skb_segment_list, the other skbs in frag_list has
different network_header(24) and transport_header(44), so there will be 20
bytes different from original,that is difference between ipv6 header and
ipv4 header. Just change transport_header to be the same with original.

Actually, there are two solutions to fix it, one is traversing all skbs
and changing every skb header in bpf_skb_proto_6_to_4, the other is
modifying frag_list skb's header in skb_segment_list. Considering
efficiency, adopt the second one--- when the first skb and other skbs in
frag_list has different network_header length, restore them to make sure
right udp payload is delivered to user space.

Signed-off-by: Lina Wang <lina.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/core/skbuff.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 180fa6a26ad4..708cc9b1b176 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3896,7 +3896,7 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb,
 	unsigned int delta_len = 0;
 	struct sk_buff *tail = NULL;
 	struct sk_buff *nskb, *tmp;
-	int err;
+	int len_diff, err;
 
 	skb_push(skb, -skb_network_offset(skb) + offset);
 
@@ -3936,9 +3936,11 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb,
 		skb_push(nskb, -skb_network_offset(nskb) + offset);
 
 		skb_release_head_state(nskb);
+		len_diff = skb_network_header_len(nskb) - skb_network_header_len(skb);
 		__copy_skb_header(nskb, skb);
 
 		skb_headers_offset_update(nskb, skb_headroom(nskb) - skb_headroom(skb));
+		nskb->transport_header += len_diff;
 		skb_copy_from_linear_data_offset(skb, -tnl_hlen,
 						 nskb->data - tnl_hlen,
 						 offset + tnl_hlen);
-- 
2.35.1