Commit 967c05ae authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller

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: 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>
parent 5f3e2bf0
...@@ -155,6 +155,7 @@ static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk) ...@@ -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 = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
mss = min(net->ipv4.sysctl_tcp_base_mss, mss); mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
mss = max(mss, 68 - tcp_sk(sk)->tcp_header_len); 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); icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
} }
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
......
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