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ipv4: use RCU protection in ip_dst_mtu_maybe_forward()

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ip_dst_mtu_maybe_forward() must use RCU protection to make
sure the net structure it reads does not disappear.

Fixes: f87c10a8aa ("ipv4: introduce ip_dst_mtu_maybe_forward and protect forwarding path against pmtu spoofing")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250205155120.1676781-4-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2025-02-05 15:51:11 +00:00 • committed by Jakub Kicinski
parent 469308552c
commit 071d801286
1 changed files with 10 additions and 3 deletions
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13
include/net/ip.h
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@ -471,9 +471,12 @@ static inline unsigned int ip_dst_mtu_maybe_forward(const struct dst_entry *dst,
bool forwarding)
{
const struct rtable *rt = dst_rtable(dst);
struct net *net = dev_net(dst->dev);
unsigned int mtu;
unsigned int mtu, res;
struct net *net;
rcu_read_lock();
net = dev_net_rcu(dst->dev);
if (READ_ONCE(net->ipv4.sysctl_ip_fwd_use_pmtu) ||
ip_mtu_locked(dst) ||
!forwarding) {
@ -497,7 +500,11 @@ static inline unsigned int ip_dst_mtu_maybe_forward(const struct dst_entry *dst,
out:
mtu = min_t(unsigned int, mtu, IP_MAX_MTU);
return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
res = mtu - lwtunnel_headroom(dst->lwtstate, mtu);
rcu_read_unlock();
return res;
}
static inline unsigned int ip_skb_dst_mtu(struct sock *sk,