From 1cee1b3f41582e4e48d4202711d4c8479bd44bab Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sat, 8 Jun 2019 10:22:49 -0700 Subject: [PATCH] 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 Reported-by: Jonathan Lemon Cc: Jonathan Looney Acked-by: Neal Cardwell Cc: Yuchung Cheng Cc: Tyler Hicks Cc: Bruce Curtis Signed-off-by: David S. Miller [Salvatore Bonaccorso: Backport for context changes in 4.9.168] [bwh: Backported to 3.16: The sysctl is global] Signed-off-by: Ben Hutchings Signed-off-by: Kevin F. Haggerty Change-Id: I53ed37a87f53cfcfd7b0e862abc0d92a3bcda274 --- net/ipv4/tcp_timer.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index d1b47922054..01a60c67e42 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -156,6 +156,7 @@ 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(sysctl_tcp_base_mss, mss); mss = max(mss, 68 - tp->tcp_header_len); + mss = max(mss, sysctl_tcp_min_snd_mss); icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); }