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Commit 7e909628 authored by Eric Dumazet's avatar Eric Dumazet Committed by Greg Kroah-Hartman
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tcp: enforce tcp_min_snd_mss in tcp_mtu_probing() 



commit 967c05aee439e6e5d7d805e195b3a20ef5c433d6 upstream.

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: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarJonathan Lemon <jonathan.lemon@gmail.com>
Cc: Jonathan Looney <jtl@netflix.com>
Acked-by: default avatarNeal 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: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 8e39cbc0

net/ipv4/tcp_timer.c

+1 −0
Original line number Diff line number Diff line
@@ -140,6 +140,7 @@ 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 - tp->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);

		}