queue-4.14/tcp-enforce-tcp_min_snd_mss-in-tcp_mtu_probing.patch

   1 From foo@baz Mon 17 Jun 2019 06:56:41 PM CEST
   2 From: Eric Dumazet <edumazet@google.com>
   3 Date: Sat, 15 Jun 2019 17:47:27 -0700
   4 Subject: tcp: enforce tcp_min_snd_mss in tcp_mtu_probing()
   5
   6 From: Eric Dumazet <edumazet@google.com>
   7
   8 commit 967c05aee439e6e5d7d805e195b3a20ef5c433d6 upstream.
   9
  10 If mtu probing is enabled tcp_mtu_probing() could very well end up
  11 with a too small MSS.
  12
  13 Use the new sysctl tcp_min_snd_mss to make sure MSS search
  14 is performed in an acceptable range.
  15
  16 CVE-2019-11479 -- tcp mss hardcoded to 48
  17
  18 Signed-off-by: Eric Dumazet <edumazet@google.com>
  19 Reported-by: Jonathan Lemon <jonathan.lemon@gmail.com>
  20 Cc: Jonathan Looney <jtl@netflix.com>
  21 Acked-by: Neal Cardwell <ncardwell@google.com>
  22 Cc: Yuchung Cheng <ycheng@google.com>
  23 Cc: Tyler Hicks <tyhicks@canonical.com>
  24 Cc: Bruce Curtis <brucec@netflix.com>
  25 Signed-off-by: David S. Miller <davem@davemloft.net>
  26 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  27 ---
  28  net/ipv4/tcp_timer.c |    1 +
  29  1 file changed, 1 insertion(+)
  30
  31 --- a/net/ipv4/tcp_timer.c
  32 +++ b/net/ipv4/tcp_timer.c
  33 @@ -141,6 +141,7 @@ static void tcp_mtu_probing(struct inet_
  34                         mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
  35                         mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
  36                         mss = max(mss, 68 - tp->tcp_header_len);
  37 +                       mss = max(mss, net->ipv4.sysctl_tcp_min_snd_mss);
  38                         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
  39                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
  40                 }