[PATCH 4.14 33/82] tcp: annotate data races around tp->mtu_info

Greg Kroah-Hartman
2021-07-26T15:48:19Z

From: Eric Dumazet <edumazet@google.com>

commit 561022acb1ce62e50f7a8258687a21b84282a4cb upstream.

While tp->mtu_info is read while socket is owned, the write
sides happen from err handlers (tcp_v[46]_mtu_reduced)
which only own the socket spinlock.

Fixes: 563d34d05786 ("tcp: dont drop MTU reduction indications")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/tcp_ipv4.c | 4 ++--
net/ipv6/tcp_ipv6.c | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)

--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -285,7 +285,7 @@ void tcp_v4_mtu_reduced(struct sock *sk)

if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
return;
- mtu = tcp_sk(sk)->mtu_info;
+ mtu = READ_ONCE(tcp_sk(sk)->mtu_info);
dst = inet_csk_update_pmtu(sk, mtu);
if (!dst)
return;
@@ -453,7 +453,7 @@ void tcp_v4_err(struct sk_buff *icmp_skb
if (sk->sk_state == TCP_LISTEN)
goto out;

- tp->mtu_info = info;
+ WRITE_ONCE(tp->mtu_info, info);
if (!sock_owned_by_user(sk)) {
tcp_v4_mtu_reduced(sk);
} else {
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -323,7 +323,7 @@ static void tcp_v6_mtu_reduced(struct so
if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
return;

- dst = inet6_csk_update_pmtu(sk, tcp_sk(sk)->mtu_info);
+ dst = inet6_csk_update_pmtu(sk, READ_ONCE(tcp_sk(sk)->mtu_info));
if (!dst)
return;

@@ -412,7 +412,7 @@ static void tcp_v6_err(struct sk_buff *s
if (!ip6_sk_accept_pmtu(sk))
goto out;

- tp->mtu_info = ntohl(info);
+ WRITE_ONCE(tp->mtu_info, ntohl(info));
if (!sock_owned_by_user(sk))
tcp_v6_mtu_reduced(sk);
else if (!test_and_set_bit(TCP_MTU_REDUCED_DEFERRED,