• Eric Dumazet's avatar
    tcp: add tcp_min_snd_mss sysctl · e757d052
    Eric Dumazet authored
    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 c39508d6 ("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: 's avatarEric Dumazet <edumazet@google.com>
    Suggested-by: 's avatarJonathan Looney <jtl@netflix.com>
    Acked-by: 's avatarNeal 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: 's avatarDavid S. Miller <davem@davemloft.net>
    Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    e757d052
Name
Last commit
Last update
Documentation Loading commit data...
arch Loading commit data...
block Loading commit data...
certs Loading commit data...
crypto Loading commit data...
drivers Loading commit data...
firmware Loading commit data...
fs Loading commit data...
include Loading commit data...
init Loading commit data...
ipc Loading commit data...
kernel Loading commit data...
lib Loading commit data...
mm Loading commit data...
net Loading commit data...
samples Loading commit data...
scripts Loading commit data...
security Loading commit data...
sound Loading commit data...
tools Loading commit data...
usr Loading commit data...
virt Loading commit data...
.get_maintainer.ignore Loading commit data...
.gitignore Loading commit data...
.mailmap Loading commit data...
COPYING Loading commit data...
CREDITS Loading commit data...
Kbuild Loading commit data...
Kconfig Loading commit data...
MAINTAINERS Loading commit data...
Makefile Loading commit data...
README Loading commit data...
REPORTING-BUGS Loading commit data...