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authorTom Herbert <tom@quantonium.net>2017-10-31 00:16:00 +0300
committerDavid S. Miller <davem@davemloft.net>2017-11-03 03:50:22 +0300
commit47d3d7ac656a1ffb9d0f0d3c845663ed6fd7e78d (patch)
treeadb397853601ba03f23c3735b3addb496319706d /Documentation
parent2d2faaf0568b4946d9abeb4e541227b4ca259840 (diff)
downloadlinux-47d3d7ac656a1ffb9d0f0d3c845663ed6fd7e78d.tar.xz
ipv6: Implement limits on Hop-by-Hop and Destination options
RFC 8200 (IPv6) defines Hop-by-Hop options and Destination options extension headers. Both of these carry a list of TLVs which is only limited by the maximum length of the extension header (2048 bytes). By the spec a host must process all the TLVs in these options, however these could be used as a fairly obvious denial of service attack. I think this could in fact be a significant DOS vector on the Internet, one mitigating factor might be that many FWs drop all packets with EH (and obviously this is only IPv6) so an Internet wide attack might not be so effective (yet!). By my calculation, the worse case packet with TLVs in a standard 1500 byte MTU packet that would be processed by the stack contains 1282 invidual TLVs (including pad TLVS) or 724 two byte TLVs. I wrote a quick test program that floods a whole bunch of these packets to a host and sure enough there is substantial time spent in ip6_parse_tlv. These packets contain nothing but unknown TLVS (that are ignored), TLV padding, and bogus UDP header with zero payload length. 25.38% [kernel] [k] __fib6_clean_all 21.63% [kernel] [k] ip6_parse_tlv 4.21% [kernel] [k] __local_bh_enable_ip 2.18% [kernel] [k] ip6_pol_route.isra.39 1.98% [kernel] [k] fib6_walk_continue 1.88% [kernel] [k] _raw_write_lock_bh 1.65% [kernel] [k] dst_release This patch adds configurable limits to Destination and Hop-by-Hop options. There are three limits that may be set: - Limit the number of options in a Hop-by-Hop or Destination options extension header. - Limit the byte length of a Hop-by-Hop or Destination options extension header. - Disallow unrecognized options in a Hop-by-Hop or Destination options extension header. The limits are set in corresponding sysctls: ipv6.sysctl.max_dst_opts_cnt ipv6.sysctl.max_hbh_opts_cnt ipv6.sysctl.max_dst_opts_len ipv6.sysctl.max_hbh_opts_len If a max_*_opts_cnt is less than zero then unknown TLVs are disallowed. The number of known TLVs that are allowed is the absolute value of this number. If a limit is exceeded when processing an extension header the packet is dropped. Default values are set to 8 for options counts, and set to INT_MAX for maximum length. Note the choice to limit options to 8 is an arbitrary guess (roughly based on the fact that the stack supports three HBH options and just one destination option). These limits have being proposed in draft-ietf-6man-rfc6434-bis. Tested (by Martin Lau) I tested out 1 thread (i.e. one raw_udp process). I changed the net.ipv6.max_dst_(opts|hbh)_number between 8 to 2048. With sysctls setting to 2048, the softirq% is packed to 100%. With 8, the softirq% is almost unnoticable from mpstat. v2; - Code and documention cleanup. - Change references of RFC2460 to be RFC8200. - Add reference to RFC6434-bis where the limits will be in standard. Signed-off-by: Tom Herbert <tom@quantonium.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/networking/ip-sysctl.txt24
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 77f4de59dc9c..e6661b205f72 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1385,6 +1385,30 @@ mld_qrv - INTEGER
Default: 2 (as specified by RFC3810 9.1)
Minimum: 1 (as specified by RFC6636 4.5)
+max_dst_opts_cnt - INTEGER
+ Maximum number of non-padding TLVs allowed in a Destination
+ options extension header. If this value is less than zero
+ then unknown options are disallowed and the number of known
+ TLVs allowed is the absolute value of this number.
+ Default: 8
+
+max_hbh_opts_cnt - INTEGER
+ Maximum number of non-padding TLVs allowed in a Hop-by-Hop
+ options extension header. If this value is less than zero
+ then unknown options are disallowed and the number of known
+ TLVs allowed is the absolute value of this number.
+ Default: 8
+
+max dst_opts_len - INTEGER
+ Maximum length allowed for a Destination options extension
+ header.
+ Default: INT_MAX (unlimited)
+
+max hbh_opts_len - INTEGER
+ Maximum length allowed for a Hop-by-Hop options extension
+ header.
+ Default: INT_MAX (unlimited)
+
IPv6 Fragmentation:
ip6frag_high_thresh - INTEGER