ip: Fix data-races around sysctl_ip_fwd_use_pmtu.

[ Upstream commit 60c158dc7b1f0558f6cadd5b50d0386da0000d50 ]

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

Fixes: f87c10a8aa1e ("ipv4: introduce ip_dst_mtu_maybe_forward and protect forwarding path against pmtu spoofing")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/net/ip.h b/include/net/ip.h
index a77a9e1c6c047f55e70a8472f2ad64d9c1811917..c69dd114f367ba09c4a0cdcf92ec31f5d013ceff 100644 (file)
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -441,7 +441,7 @@ static inline unsigned int ip_dst_mtu_maybe_forward(const struct dst_entry *dst,
        struct net *net = dev_net(dst->dev);
        unsigned int mtu;
 
-       if (net->ipv4.sysctl_ip_fwd_use_pmtu ||
+       if (READ_ONCE(net->ipv4.sysctl_ip_fwd_use_pmtu) ||
            ip_mtu_locked(dst) ||
            !forwarding) {
                mtu = rt->rt_pmtu;

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 1db2fda2283066ac99972f445b2668dd54a1a450..7f08a30256c52ba58b328ece28fff2494f459d6d 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1404,7 +1404,7 @@ u32 ip_mtu_from_fib_result(struct fib_result *res, __be32 daddr)
        struct fib_info *fi = res->fi;
        u32 mtu = 0;
 
-       if (dev_net(dev)->ipv4.sysctl_ip_fwd_use_pmtu ||
+       if (READ_ONCE(dev_net(dev)->ipv4.sysctl_ip_fwd_use_pmtu) ||
            fi->fib_metrics->metrics[RTAX_LOCK - 1] & (1 << RTAX_MTU))
                mtu = fi->fib_mtu;