diff options
| author | Eric Dumazet <edumazet@google.com> | 2019-06-15 17:44:24 -0700 |
|---|---|---|
| committer | Jason Liu <jason.hui.liu@nxp.com> | 2019-09-06 15:49:42 +0800 |
| commit | 77680b463999012cd7651d68b15300333d5ddd88 (patch) | |
| tree | 98b2c4e0b507818fd851a8299c0998df98a4c61c /net | |
| parent | b9fe6ea6a01e43c0e75cf8fa017beccd716f203f (diff) | |
tcp: add tcp_min_snd_mss sysctl
commit 5f3e2bf008c2221478101ee72f5cb4654b9fc363 upstream.
Some TCP peers announce a very small MSS option in their SYN and/or
SYN/ACK messages.
This forces the stack to send packets with a very high network/cpu
overhead.
Linux has enforced a minimal value of 48. Since this value includes
the size of TCP options, and that the options can consume up to 40
bytes, this means that each segment can include only 8 bytes of payload.
In some cases, it can be useful to increase the minimal value
to a saner value.
We still let the default to 48 (TCP_MIN_SND_MSS), for compatibility
reasons.
Note that TCP_MAXSEG socket option enforces a minimal value
of (TCP_MIN_MSS). David Miller increased this minimal value
in commit c39508d6f118 ("tcp: Make TCP_MAXSEG minimum more correct.")
from 64 to 88.
We might in the future merge TCP_MIN_SND_MSS and TCP_MIN_MSS.
CVE-2019-11479 -- tcp mss hardcoded to 48
Signed-off-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Jonathan Looney <jtl@netflix.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Tyler Hicks <tyhicks@canonical.com>
Cc: Bruce Curtis <brucec@netflix.com>
Cc: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit cd6f35b8421ff20365ff711c0ac7647fd70e9af7)
Diffstat (limited to 'net')
| -rw-r--r-- | net/ipv4/sysctl_net_ipv4.c | 11 | ||||
| -rw-r--r-- | net/ipv4/tcp_ipv4.c | 1 | ||||
| -rw-r--r-- | net/ipv4/tcp_output.c | 3 |
3 files changed, 13 insertions, 2 deletions
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c index d82e8344fc54..d1a31473bcde 100644 --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -37,6 +37,8 @@ static int ip_local_port_range_min[] = { 1, 1 }; static int ip_local_port_range_max[] = { 65535, 65535 }; static int tcp_adv_win_scale_min = -31; static int tcp_adv_win_scale_max = 31; +static int tcp_min_snd_mss_min = TCP_MIN_SND_MSS; +static int tcp_min_snd_mss_max = 65535; static int ip_privileged_port_min; static int ip_privileged_port_max = 65535; static int ip_ttl_min = 1; @@ -941,6 +943,15 @@ static struct ctl_table ipv4_net_table[] = { .proc_handler = proc_dointvec, }, { + .procname = "tcp_min_snd_mss", + .data = &init_net.ipv4.sysctl_tcp_min_snd_mss, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = &tcp_min_snd_mss_min, + .extra2 = &tcp_min_snd_mss_max, + }, + { .procname = "tcp_probe_threshold", .data = &init_net.ipv4.sysctl_tcp_probe_threshold, .maxlen = sizeof(int), diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 97a414dbdaf4..0569718e3656 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -2477,6 +2477,7 @@ static int __net_init tcp_sk_init(struct net *net) net->ipv4.sysctl_tcp_ecn_fallback = 1; net->ipv4.sysctl_tcp_base_mss = TCP_BASE_MSS; + net->ipv4.sysctl_tcp_min_snd_mss = TCP_MIN_SND_MSS; net->ipv4.sysctl_tcp_probe_threshold = TCP_PROBE_THRESHOLD; net->ipv4.sysctl_tcp_probe_interval = TCP_PROBE_INTERVAL; diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 36d1945b48f1..a8772e11dc1c 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1447,8 +1447,7 @@ static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu) mss_now -= icsk->icsk_ext_hdr_len; /* Then reserve room for full set of TCP options and 8 bytes of data */ - if (mss_now < TCP_MIN_SND_MSS) - mss_now = TCP_MIN_SND_MSS; + mss_now = max(mss_now, sock_net(sk)->ipv4.sysctl_tcp_min_snd_mss); return mss_now; } |