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: Eric Dumazet <[email protected]> Reported-by: Jonathan Lemon <[email protected]> Cc: Jonathan Looney <[email protected]> Acked-by: Neal Cardwell <[email protected]> Cc: Yuchung Cheng <[email protected]> Cc: Tyler Hicks <[email protected]> Cc: Bruce Curtis <[email protected]> Signed-off-by: David S. Miller <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
klaby · Jun 17, 2019 · 7e90962 · 7e90962
1 parent 8e39cbc
commit 7e90962
Showing 1 changed file with 1 addition and 0 deletions.
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
@@ -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);
 		}