[PATCH 5.15 091/201] tcp: Fix data-races around sysctl_tcp_syn(ack)?_retries.

Greg Kroah-Hartman
2022-07-27T17:10:55Z

From: Kuniyuki Iwashima <kuniyu@amazon.com>

[ Upstream commit 20a3b1c0f603e8c55c3396abd12dfcfb523e4d3c ]

While reading sysctl_tcp_syn(ack)?_retries, they can be changed
concurrently. Thus, we need to add READ_ONCE() to their readers.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
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>
---
net/ipv4/inet_connection_sock.c | 3 ++-
net/ipv4/tcp.c | 3 ++-
net/ipv4/tcp_timer.c | 10 +++++++---
3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index d3bbb344bbe1..a53f9bf7886f 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -829,7 +829,8 @@ static void reqsk_timer_handler(struct timer_list *t)

icsk = inet_csk(sk_listener);
net = sock_net(sk_listener);
- max_syn_ack_retries = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_synack_retries;
+ max_syn_ack_retries = icsk->icsk_syn_retries ? :
+ READ_ONCE(net->ipv4.sysctl_tcp_synack_retries);
/* Normally all the openreqs are young and become mature
* (i.e. converted to established socket) for first timeout.
* If synack was not acknowledged for 1 second, it means
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 4ac53c8f0583..e22a61b2ba82 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3974,7 +3974,8 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
val = keepalive_probes(tp);
break;
case TCP_SYNCNT:
- val = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
+ val = icsk->icsk_syn_retries ? :
+ READ_ONCE(net->ipv4.sysctl_tcp_syn_retries);
break;
case TCP_LINGER2:
val = tp->linger2;
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 4f3b9ab222b6..a234704e8163 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -239,7 +239,8 @@ static int tcp_write_timeout(struct sock *sk)
if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
if (icsk->icsk_retransmits)
__dst_negative_advice(sk);
- retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
+ retry_until = icsk->icsk_syn_retries ? :
+ READ_ONCE(net->ipv4.sysctl_tcp_syn_retries);
expired = icsk->icsk_retransmits >= retry_until;
} else {
if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0)) {
@@ -406,12 +407,15 @@ abort: tcp_write_err(sk);
static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
{
struct inet_connection_sock *icsk = inet_csk(sk);
- int max_retries = icsk->icsk_syn_retries ? :
- sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
struct tcp_sock *tp = tcp_sk(sk);
+ int max_retries;

req->rsk_ops->syn_ack_timeout(req);

+ /* add one more retry for fastopen */
+ max_retries = icsk->icsk_syn_retries ? :
+ READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_synack_retries) + 1;
+
if (req->num_timeout >= max_retries) {
tcp_write_err(sk);
return;
--
2.35.1