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 76aaa7eb5b823c67bff26d186d2351d18d2c1c00..a7e40ef02732f53eaed16f18acad2f9cf240cb21 100644 (file)
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -440,7 +440,7 @@ 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)
                return dst_mtu(dst);

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index aab8ac383d5d1de1edc0e45a38cec7e8850fa995..374647693d7acc64420b6435d508b1e48025fe5c 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1442,7 +1442,7 @@ 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;