[PATCH 5.4 32/87] tcp: Fix data-races around sysctl_tcp_syncookies.

Greg Kroah-Hartman
2022-07-27T16:41:00Z

From: Kuniyuki Iwashima <kuniyu@amazon.com>

[ Upstream commit f2e383b5bb6bbc60a0b94b87b3e49a2b1aefd11e ]

While reading sysctl_tcp_syncookies, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its 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/core/filter.c | 4 ++--
net/ipv4/syncookies.c | 3 ++-
net/ipv4/tcp_input.c | 20 ++++++++++++--------
net/ipv6/syncookies.c | 3 ++-
4 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 75f53b5e6389..72bf78032f45 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5839,7 +5839,7 @@ BPF_CALL_5(bpf_tcp_check_syncookie, struct sock *, sk, void *, iph, u32, iph_len
if (sk->sk_protocol != IPPROTO_TCP || sk->sk_state != TCP_LISTEN)
return -EINVAL;

- if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies)
+ if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies))
return -EINVAL;

if (!th->ack || th->rst || th->syn)
@@ -5914,7 +5914,7 @@ BPF_CALL_5(bpf_tcp_gen_syncookie, struct sock *, sk, void *, iph, u32, iph_len,
if (sk->sk_protocol != IPPROTO_TCP || sk->sk_state != TCP_LISTEN)
return -EINVAL;

- if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies)
+ if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies))
return -ENOENT;

if (!th->syn || th->ack || th->fin || th->rst)
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 6811174ad518..f1cbf8911844 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -297,7 +297,8 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
struct flowi4 fl4;
u32 tsoff = 0;

- if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
+ if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) ||
+ !th->ack || th->rst)
goto out;

if (tcp_synq_no_recent_overflow(sk))
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0808110451a0..85204903b2fa 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6530,11 +6530,14 @@ static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
{
struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
const char *msg = "Dropping request";
- bool want_cookie = false;
struct net *net = sock_net(sk);
+ bool want_cookie = false;
+ u8 syncookies;
+
+ syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);

#ifdef CONFIG_SYN_COOKIES
- if (net->ipv4.sysctl_tcp_syncookies) {
+ if (syncookies) {
msg = "Sending cookies";
want_cookie = true;
__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
@@ -6542,8 +6545,7 @@ static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
#endif
__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);

- if (!queue->synflood_warned &&
- net->ipv4.sysctl_tcp_syncookies != 2 &&
+ if (!queue->synflood_warned && syncookies != 2 &&
xchg(&queue->synflood_warned, 1) == 0)
net_info_ratelimited("%s: Possible SYN flooding on port %d. %s. Check SNMP counters.\n",
proto, sk->sk_num, msg);
@@ -6578,7 +6580,7 @@ u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
struct tcp_sock *tp = tcp_sk(sk);
u16 mss;

- if (sock_net(sk)->ipv4.sysctl_tcp_syncookies != 2 &&
+ if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) != 2 &&
!inet_csk_reqsk_queue_is_full(sk))
return 0;

@@ -6612,13 +6614,15 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
bool want_cookie = false;
struct dst_entry *dst;
struct flowi fl;
+ u8 syncookies;
+
+ syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);

/* TW buckets are converted to open requests without
* limitations, they conserve resources and peer is
* evidently real one.
*/
- if ((net->ipv4.sysctl_tcp_syncookies == 2 ||
- inet_csk_reqsk_queue_is_full(sk)) && !isn) {
+ if ((syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) && !isn) {
want_cookie = tcp_syn_flood_action(sk, rsk_ops->slab_name);
if (!want_cookie)
goto drop;
@@ -6669,7 +6673,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,

if (!want_cookie && !isn) {
/* Kill the following clause, if you dislike this way. */
- if (!net->ipv4.sysctl_tcp_syncookies &&
+ if (!syncookies &&
(net->ipv4.sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
(net->ipv4.sysctl_max_syn_backlog >> 2)) &&
!tcp_peer_is_proven(req, dst)) {
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 37ab254f7b92..7e5550546594 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -141,7 +141,8 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
__u8 rcv_wscale;
u32 tsoff = 0;

- if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
+ if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) ||
+ !th->ack || th->rst)
goto out;

if (tcp_synq_no_recent_overflow(sk))
--
2.35.1