tcp: Fix data-races around sysctl_tcp_min_snd_mss.

While reading sysctl_tcp_min_snd_mss, it can be changed concurrently. Thus, we need to add READ_ONCE() to its readers. Fixes: 5f3e2bf ("tcp: add tcp_min_snd_mss sysctl") Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> Signed-off-by: David S. Miller <davem@davemloft.net>
angolini · Jul 15, 2022 · 78eb166 · 78eb166
1 parent 88d78bc
commit 78eb166
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Showing 2 changed files with 3 additions and 2 deletions.
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
@@ -1719,7 +1719,8 @@ static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
 	mss_now -= icsk->icsk_ext_hdr_len;
 
 	/* Then reserve room for full set of TCP options and 8 bytes of data */
-	mss_now = max(mss_now, sock_net(sk)->ipv4.sysctl_tcp_min_snd_mss);
+	mss_now = max(mss_now,
+		      READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_snd_mss));
 	return mss_now;
 }
 

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
@@ -173,7 +173,7 @@ static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 		mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 		mss = min(READ_ONCE(net->ipv4.sysctl_tcp_base_mss), mss);
 		mss = max(mss, net->ipv4.sysctl_tcp_mtu_probe_floor);
-		mss = max(mss, net->ipv4.sysctl_tcp_min_snd_mss);
+		mss = max(mss, READ_ONCE(net->ipv4.sysctl_tcp_min_snd_mss));
 		icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 	}
 	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);