[PATCH 4.19 07/62] ip: Fix data-races around sysctl_ip_fwd_use_pmtu.

Greg Kroah-Hartman
2022-07-27T16:31:19Z

From: Kuniyuki Iwashima <kuniyu@amazon.com>

[ 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>
---
include/net/ip.h | 2 +-
net/ipv4/route.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/net/ip.h b/include/net/ip.h
index d1a4efedbc03..471463bfe6f9 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -402,7 +402,7 @@ 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 d7f17581df7d..57e2316529d0 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1419,7 +1419,7 @@ u32 ip_mtu_from_fib_result(struct fib_result *res, __be32 daddr)
struct net_device *dev = nh->nh_dev;
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;

--
2.35.1