ip: Fix data-races around sysctl_ip_fwd_update_priority.

stable inclusion
from stable-v5.10.134
commit 11038fa781ab916535c53351537b22d6d405667d
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5ZVR7

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=11038fa781ab916535c53351537b22d6d405667d

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

[ Upstream commit 7bf9e18d ]

While reading sysctl_ip_fwd_update_priority, it can be changed
concurrently.  Thus, we need to add READ_ONCE() to its readers.

Fixes: 432e05d3 ("net: ipv4: Control SKB reprioritization after forwarding")
Signed-off-by: NKuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c

@@ -8038,13 +8038,14 @@ static int mlxsw_sp_dscp_init(struct mlxsw_sp *mlxsw_sp)
 static int __mlxsw_sp_router_init(struct mlxsw_sp *mlxsw_sp)
 {
 	struct net *net = mlxsw_sp_net(mlxsw_sp);
-	bool usp = net->ipv4.sysctl_ip_fwd_update_priority;
 	char rgcr_pl[MLXSW_REG_RGCR_LEN];
 	u64 max_rifs;
+	bool usp;
 
 	if (!MLXSW_CORE_RES_VALID(mlxsw_sp->core, MAX_RIFS))
 		return -EIO;
 	max_rifs = MLXSW_CORE_RES_GET(mlxsw_sp->core, MAX_RIFS);
+	usp = READ_ONCE(net->ipv4.sysctl_ip_fwd_update_priority);
 
 	mlxsw_reg_rgcr_pack(rgcr_pl, true, true);
 	mlxsw_reg_rgcr_max_router_interfaces_set(rgcr_pl, max_rifs);

net/ipv4/ip_forward.c

@@ -151,7 +151,7 @@ int ip_forward(struct sk_buff *skb)
 	    !skb_sec_path(skb))
 		ip_rt_send_redirect(skb);
 
-	if (net->ipv4.sysctl_ip_fwd_update_priority)
+	if (READ_ONCE(net->ipv4.sysctl_ip_fwd_update_priority))
 		skb->priority = rt_tos2priority(iph->tos);
 
 	return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD,