tcp: Fix a data-race around sysctl_tcp_frto.

BugLink: https://bugs.launchpad.net/bugs/1989218
commit 706c6202a3589f290e1ef9be0584a8f4a3cc0507 upstream.

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

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 1c940517f5f50d5d922811cc1cf5e853346f81dc..b9fd51826aea61e84502f7b7921c8f68c7c5b9b3 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2167,7 +2167,7 @@ void tcp_enter_loss(struct sock *sk)
         * loss recovery is underway except recurring timeout(s) on
         * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
         */
-       tp->frto = net->ipv4.sysctl_tcp_frto &&
+       tp->frto = READ_ONCE(net->ipv4.sysctl_tcp_frto) &&
                   (new_recovery || icsk->icsk_retransmits) &&
                   !inet_csk(sk)->icsk_mtup.probe_size;
 }