From 8ed1dc44d3e9e8387a104b1ae8f92e9a3fbf1b1e Mon Sep 17 00:00:00 2001 From: Hannes Frederic Sowa Date: Thu, 9 Jan 2014 10:01:17 +0100 Subject: ipv4: introduce hardened ip_no_pmtu_disc mode This new ip_no_pmtu_disc mode only allowes fragmentation-needed errors to be honored by protocols which do more stringent validation on the ICMP's packet payload. This knob is useful for people who e.g. want to run an unmodified DNS server in a namespace where they need to use pmtu for TCP connections (as they are used for zone transfers or fallback for requests) but don't want to use possibly spoofed UDP pmtu information. Currently the whitelisted protocols are TCP, SCTP and DCCP as they check if the returned packet is in the window or if the association is valid. Cc: Eric Dumazet Cc: David Miller Cc: John Heffner Suggested-by: Florian Weimer Signed-off-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- Documentation/networking/ip-sysctl.txt | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index 0d71fa962d8a..c97932c88ea3 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -26,7 +26,18 @@ ip_no_pmtu_disc - INTEGER discarded. Outgoing frames are handled the same as in mode 1, implicitly setting IP_PMTUDISC_DONT on every created socket. - Possible values: 0-2 + Mode 3 is a hardend pmtu discover mode. The kernel will only + accept fragmentation-needed errors if the underlying protocol + can verify them besides a plain socket lookup. Current + protocols for which pmtu events will be honored are TCP, SCTP + and DCCP as they verify e.g. the sequence number or the + association. This mode should not be enabled globally but is + only intended to secure e.g. name servers in namespaces where + TCP path mtu must still work but path MTU information of other + protocols should be discarded. If enabled globally this mode + could break other protocols. + + Possible values: 0-3 Default: FALSE min_pmtu - INTEGER -- cgit v1.2.3