linux-kernel - [PATCH v1 net 5/5] tcp: Fix data races around icsk->icsk_af

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Date:   Tue, 27 Sep 2022 09:12:09 -0700
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        David Ahern <dsahern@...nel.org>
CC:     Kuniyuki Iwashima <kuniyu@...zon.com>,
        Kuniyuki Iwashima <kuni1840@...il.com>,
        <netdev@...r.kernel.org>, <syzkaller-bugs@...glegroups.com>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH v1 net 5/5] tcp: Fix data races around icsk->icsk_af_ops.

IPV6_ADDRFORM changes icsk->icsk_af_ops under lock_sock(), but
tcp_(get|set)sockopt() read it locklessly.  To avoid load/store
tearing, we need to add READ_ONCE() and WRITE_ONCE() for the reads
and write.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
 net/ipv4/tcp.c           | 10 ++++++----
 net/ipv6/ipv6_sockglue.c |  3 ++-
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e373dde1f46f..c86dd0ccef5b 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3795,8 +3795,9 @@ int tcp_setsockopt(struct sock *sk, int level, int optname, sockptr_t optval,
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 
 	if (level != SOL_TCP)
-		return icsk->icsk_af_ops->setsockopt(sk, level, optname,
-						     optval, optlen);
+		/* IPV6_ADDRFORM can change icsk->icsk_af_ops under us. */
+		return READ_ONCE(icsk->icsk_af_ops)->setsockopt(sk, level, optname,
+								optval, optlen);
 	return do_tcp_setsockopt(sk, level, optname, optval, optlen);
 }
 EXPORT_SYMBOL(tcp_setsockopt);
@@ -4394,8 +4395,9 @@ int tcp_getsockopt(struct sock *sk, int level, int optname, char __user *optval,
 	struct inet_connection_sock *icsk = inet_csk(sk);
 
 	if (level != SOL_TCP)
-		return icsk->icsk_af_ops->getsockopt(sk, level, optname,
-						     optval, optlen);
+		/* IPV6_ADDRFORM can change icsk->icsk_af_ops under us. */
+		return READ_ONCE(icsk->icsk_af_ops)->getsockopt(sk, level, optname,
+								optval, optlen);
 	return do_tcp_getsockopt(sk, level, optname, optval, optlen);
 }
 EXPORT_SYMBOL(tcp_getsockopt);
diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index a89db5872dc3..726d95859898 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -479,7 +479,8 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 
 				/* Paired with READ_ONCE(sk->sk_prot) in inet6_stream_ops */
 				WRITE_ONCE(sk->sk_prot, &tcp_prot);
-				icsk->icsk_af_ops = &ipv4_specific;
+				/* Paired with READ_ONCE() in tcp_(get|set)sockopt() */
+				WRITE_ONCE(icsk->icsk_af_ops, &ipv4_specific);
 				sk->sk_socket->ops = &inet_stream_ops;
 				sk->sk_family = PF_INET;
 				tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
-- 
2.30.2