diff options
| author | Eric Dumazet <edumazet@google.com> | 2019-06-06 09:15:31 -0700 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2019-06-20 18:11:28 +0100 |
| commit | 6b7e7997ad3505db7de85ff12276fc84659481d3 (patch) | |
| tree | 3cd3aadabd8db2681ca2ea460fb850bbd33c56a9 /include | |
| parent | dc97a907bc76b71c08e7e99a5b1b30ef4d5e4a85 (diff) | |
| download | linux-stable-6b7e7997ad3505db7de85ff12276fc84659481d3.tar.gz | |
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>
[Salvatore Bonaccorso: Backport for context changes in 4.9.168]
[bwh: Backported to 3.16: Make the sysctl global, consistent with
net.ipv4.tcp_base_mss]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'include')
| -rw-r--r-- | include/net/tcp.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h index 21c68c2c52a853..79762b662de3ae 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -270,6 +270,7 @@ extern int sysctl_tcp_moderate_rcvbuf; extern int sysctl_tcp_tso_win_divisor; extern int sysctl_tcp_mtu_probing; extern int sysctl_tcp_base_mss; +extern int sysctl_tcp_min_snd_mss; extern int sysctl_tcp_workaround_signed_windows; extern int sysctl_tcp_slow_start_after_idle; extern int sysctl_tcp_thin_linear_timeouts; |