Commit 967c05ae authored Jun 08, 2019 by Eric Dumazet Committed by David S. Miller Jun 15, 2019

tcp: enforce tcp_min_snd_mss in tcp_mtu_probing()



If mtu probing is enabled tcp_mtu_probing() could very well end up
with a too small MSS.

Use the new sysctl tcp_min_snd_mss to make sure MSS search
is performed in an acceptable range.

CVE-2019-11479 -- tcp mss hardcoded to 48

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Cc: Jonathan Looney <jtl@netflix.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Tyler Hicks <tyhicks@canonical.com>
Cc: Bruce Curtis <brucec@netflix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 5f3e2bf0

net/ipv4/tcp_timer.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -155,6 +155,7 @@ 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(net->ipv4.sysctl_tcp_base_mss, mss);
		mss = max(mss, 68 - tcp_sk(sk)->tcp_header_len);
		mss = max(mss, 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);

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