tcp: Fix a data-race around sysctl_tcp_limit_output_bytes.

commit 9fb90193fbd66b4c5409ef729fd081861f8b6351 upstream.

While reading sysctl_tcp_limit_output_bytes, it can be changed
concurrently.  Thus, we need to add READ_ONCE() to its reader.

Fixes: 46d3ceabd8d9 ("tcp: TCP Small Queues")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 43ecbd7..4389ad7 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2503,7 +2503,7 @@ static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
                      sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift));
        if (sk->sk_pacing_status == SK_PACING_NONE)
                limit = min_t(unsigned long, limit,
-                             sock_net(sk)->ipv4.sysctl_tcp_limit_output_bytes);
+                             READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_limit_output_bytes));
        limit <<= factor;
 
        if (static_branch_unlikely(&tcp_tx_delay_enabled) &&