net: ipv6: fix wrong start position when receive hop-by-hop fragment

[ Upstream commit 1cd354fe1e4864eeaff62f66ee513080ec946f20 ]

In IPv6, ipv6_rcv_core will parse the hop-by-hop type extension header and increase skb->transport_header by one extension header length.
But if there are more other extension headers like fragment header at this time, the skb->transport_header points to the second extension header,
not the transport layer header or the first extension header.

This will result in the start and nexthdrp variable not pointing to the same position in ipv6frag_thdr_trunced,
and ipv6_skip_exthdr returning incorrect offset and frag_off.Sometimes,the length of the last sharded packet is smaller than the calculated incorrect offset, resulting in packet loss.
We can use network header to offset and calculate the correct position to solve this problem.

Fixes: 9d9e937b1c8b (ipv6/netfilter: Discard first fragment not including all headers)
Signed-off-by: Gao Xingwang <gaoxingwang1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 28e44782c94d1e0485c9d7c685179716ab252c22..6993675171556f1eaad55a292f3a6119d6d9de69 100644 (file)
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -363,7 +363,7 @@ static int ipv6_frag_rcv(struct sk_buff *skb)
         * the source of the fragment, with the Pointer field set to zero.
         */
        nexthdr = hdr->nexthdr;
-       if (ipv6frag_thdr_truncated(skb, skb_transport_offset(skb), &nexthdr)) {
+       if (ipv6frag_thdr_truncated(skb, skb_network_offset(skb) + sizeof(struct ipv6hdr), &nexthdr)) {
                __IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
                                IPSTATS_MIB_INHDRERRORS);
                icmpv6_param_prob(skb, ICMPV6_HDR_INCOMP, 0);