xfrm: fix bug with DSCP copy to v6 from v4 tunnel

stable inclusion
from stable-v5.10.168
commit 30fdf660356f708917b722a9aa01d70d27d96280
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7URR4

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=30fdf660356f708917b722a9aa01d70d27d96280

----------------------------------------------------

[ Upstream commit 6028da3f ]

When copying the DSCP bits for decap-dscp into IPv6 don't assume the
outer encap is always IPv6. Instead, as with the inner IPv4 case, copy
the DSCP bits from the correctly saved "tos" value in the control block.

Fixes: 227620e2 ("[IPSEC]: Separate inner/outer mode processing on input")
Signed-off-by: NChristian Hopps <chopps@chopps.org>
Acked-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: Nzhaoxiaoqiang11 <zhaoxiaoqiang11@jd.com>

net/xfrm/xfrm_input.c

@@ -278,8 +278,7 @@ static int xfrm6_remove_tunnel_encap(struct xfrm_state *x, struct sk_buff *skb)
 		goto out;
 
 	if (x->props.flags & XFRM_STATE_DECAP_DSCP)
-		ipv6_copy_dscp(ipv6_get_dsfield(ipv6_hdr(skb)),
-			       ipipv6_hdr(skb));
+		ipv6_copy_dscp(XFRM_MODE_SKB_CB(skb)->tos, ipipv6_hdr(skb));
 	if (!(x->props.flags & XFRM_STATE_NOECN))
 		ipip6_ecn_decapsulate(skb);