6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ Upstream commit 071d8012869b6af352acca346ade13e7be90a49f ]
ip_dst_mtu_maybe_forward() must use RCU protection to make
sure the net structure it reads does not disappear.
Fixes: f87c10a8aa1e8 ("ipv4: introduce ip_dst_mtu_maybe_forward and protect forwarding path against pmtu spoofing")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Link: https://patch.msgid.link/20250205155120.1676781-4-edumazet@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/net/ip.h | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/include/net/ip.h b/include/net/ip.h
index d92d3bc3ec0e2..fe4f854381143 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -465,9 +465,12 @@ 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) {
@@ -491,7 +494,11 @@ 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,
--
2.39.5
