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| author |   Eric Dumazet <edumazet@google.com> | 2019-06-06 09:15:31 -0700 |
|---|---|---|
| committer |   David S. Miller <davem@davemloft.net> | 2019-06-15 18:47:31 -0700 |
| commit | 5f3e2bf008c2221478101ee72f5cb4654b9fc363 (patch) | |
| tree | 7be18a95aa24dc68564ab7d84bb158468efb8a09 /Documentation/networking/ip-sysctl.txt | |
| parent | tcp: tcp_fragment() should apply sane memory limits (diff) | |
| download | linux-dev-5f3e2bf008c2221478101ee72f5cb4654b9fc363.tar.xz linux-dev-5f3e2bf008c2221478101ee72f5cb4654b9fc363.zip | |
tcp: add tcp_min_snd_mss sysctl
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>
Diffstat (limited to 'Documentation/networking/ip-sysctl.txt')
| -rw-r--r-- | Documentation/networking/ip-sysctl.txt | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index 288aa264ac26..22f6b8b1110a 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -255,6 +255,14 @@ tcp_base_mss - INTEGER Path MTU discovery (MTU probing). If MTU probing is enabled, this is the initial MSS used by the connection. +tcp_min_snd_mss - INTEGER + TCP SYN and SYNACK messages usually advertise an ADVMSS option, + as described in RFC 1122 and RFC 6691. + If this ADVMSS option is smaller than tcp_min_snd_mss, + it is silently capped to tcp_min_snd_mss. + + Default : 48 (at least 8 bytes of payload per segment) + tcp_congestion_control - STRING Set the congestion control algorithm to be used for new connections. The algorithm "reno" is always available, but |