[PATCH net-next v3 2/2] ipv4: snapshot dst.dev in ip_rt_send_redirect() and ip_rt_get_source()
From: <hidden>
Date: 2026-07-08 06:06:43
Also in:
lkml
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
From: Xuanqiang Luo <redacted> rt_flush_dev() can replace rt->dst.dev with blackhole_netdev while RCU readers are running. ip_rt_send_redirect() and ip_rt_get_source() both read rt->dst.dev more than once and use the results in one operation. If rt->dst.dev changes between those reads, the operation can use values from two devices. For example, ip_rt_send_redirect() can use in_dev from the old device and the L3 master ifindex from blackhole_netdev. Read rt->dst.dev once in these two functions and use the snapshot for the later device accesses. Signed-off-by: Xuanqiang Luo <redacted> --- net/ipv4/route.c | 31 ++++++++++++++++++------------- 1 file changed, 18 insertions(+), 13 deletions(-)
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index b668375df71e2..4fed07cae7da2 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c@@ -874,21 +874,23 @@ void ip_rt_send_redirect(struct sk_buff *skb) { struct rtable *rt = skb_rtable(skb); struct in_device *in_dev; + struct net_device *dev; struct inet_peer *peer; - struct net *net; int log_martians; + struct net *net; int vif; rcu_read_lock(); - in_dev = __in_dev_get_rcu(rt->dst.dev); + dev = dst_dev_rcu(&rt->dst); + in_dev = __in_dev_get_rcu(dev); if (!in_dev || !IN_DEV_TX_REDIRECTS(in_dev)) { rcu_read_unlock(); return; } log_martians = IN_DEV_LOG_MARTIANS(in_dev); - vif = l3mdev_master_ifindex_rcu(rt->dst.dev); + vif = l3mdev_master_ifindex_rcu(dev); - net = dev_net(rt->dst.dev); + net = dev_net_rcu(dev); peer = inet_getpeer_v4(net->ipv4.peers, ip_hdr(skb)->saddr, vif); if (!peer) { rcu_read_unlock();
@@ -1287,29 +1289,32 @@ void ip_rt_get_source(u8 *addr, struct sk_buff *skb, struct rtable *rt) { __be32 src; - if (rt_is_output_route(rt)) + rcu_read_lock(); + if (rt_is_output_route(rt)) { src = ip_hdr(skb)->saddr; - else { - struct fib_result res; + } else { + struct net_device *dev = dst_dev_rcu(&rt->dst); + struct net *net = dev_net_rcu(dev); struct iphdr *iph = ip_hdr(skb); + struct fib_result res; struct flowi4 fl4 = { .daddr = iph->daddr, .saddr = iph->saddr, .flowi4_dscp = ip4h_dscp(iph), - .flowi4_oif = rt->dst.dev->ifindex, + .flowi4_oif = dev->ifindex, .flowi4_iif = skb->dev->ifindex, .flowi4_mark = skb->mark, }; - rcu_read_lock(); - if (fib_lookup(dev_net(rt->dst.dev), &fl4, &res, 0) == 0) - src = fib_result_prefsrc(dev_net(rt->dst.dev), &res); + if (fib_lookup(net, &fl4, &res, 0) == 0) + src = fib_result_prefsrc(net, &res); else - src = inet_select_addr(rt->dst.dev, + src = inet_select_addr(dev, rt_nexthop(rt, iph->daddr), RT_SCOPE_UNIVERSE); - rcu_read_unlock(); } + rcu_read_unlock(); + memcpy(addr, &src, 4); }
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2.43.0