6.12-stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
[ 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@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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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,