merged tcp-timestamps-disable package into security-misc package

disable conntrack helper for better security

https://phabricator.whonix.org/T486

README.md

@@ -2,10 +2,49 @@
 
 - deactivates previews in Dolphin
 - deactivates previews in Nautilus
-
-This package only takes effect for newly created user accounts. Not for
+- deactivates TCP timestamps
+- deactivates Netfilter's connection tracking helper
+.
+Changes to the file browser only take effect for newly created user accounts. Not for
 existing user accounts. This package is most useful to help Linux distribution
 maintainers setting divergent defaults.
+.
+TCP time stamps (rfc 1323) allow for tracking clock
+information with millisecond resolution. This may or may not allow an
+attacker to learn information about the system clock at such
+a resolution, depending on various issues such as network lag.
+This information is available to anyone who monitors the network
+somewhere between the attacked system and the destination server.
+It may allow an attacker to find out how long a given
+system has been running, and to distinguish several
+systems running behind NAT and using the same IP address. It might
+also allow to look for clocks that match an expected value to find the
+public IP used by a user.
+.
+Hence, this package disables this feature by shipping the
+/etc/sysctl.d/tcp_timestamps.conf configuration file.
+.
+Note that TCP time stamps normally have some usefulness. They are
+needed for:
+.
+* the TCP protection against wrapped sequence numbers; however, to
+  trigger a wrap, one needs to send roughly 2^32 packets in one
+  minute:  as said in rfc 1700, "The current recommended default
+  time to live (TTL) for the Internet Protocol (IP) [45,105] is 64".
+  So, this probably won't be a practical problem in the context
+  of Anonymity Distributions.
+.
+* "Round-Trip Time Measurement", which is only useful when the user
+  manages to saturate their connection. When using Anonymity Distributions,
+  probably the limiting factor for transmission speed is rarely the capacity
+  of the user connection.
+.
+Netfilter's connection tracking helper module increases kernel attack 
+surface by enabling superfluous functionality such as IRC parsing in 
+the kernel (!)
+.
+Hence, this package disables this feature by shipping the
+/etc/sysctl.d/nf_conntrack_helper.conf configuration file.
 
 (This package description has been [automatically](https://github.com/Whonix/whonix-developer-meta-files/blob/master/debug-steps/packaging-helper-script) extracted and mirrored from `debian/control`.)
 

debian/control

@@ -15,9 +15,48 @@ Package: security-misc
 Architecture: all
 Depends: ${misc:Depends}
 Description: enhances misc security settings
- - deactivates previews in Dolphin
- - deactivates previews in Nautilus
- .
- This package only takes effect for newly created user accounts. Not for
- existing user accounts. This package is most useful to help Linux distribution
- maintainers setting divergent defaults.
+- deactivates previews in Dolphin
+- deactivates previews in Nautilus
+- deactivates TCP timestamps
+- deactivates Netfilter's connection tracking helper
+.
+Changes to the file browser only take effect for newly created user accounts. Not for
+existing user accounts. This package is most useful to help Linux distribution
+maintainers setting divergent defaults.
+.
+TCP time stamps (rfc 1323) allow for tracking clock
+information with millisecond resolution. This may or may not allow an
+attacker to learn information about the system clock at such
+a resolution, depending on various issues such as network lag.
+This information is available to anyone who monitors the network
+somewhere between the attacked system and the destination server.
+It may allow an attacker to find out how long a given
+system has been running, and to distinguish several
+systems running behind NAT and using the same IP address. It might
+also allow to look for clocks that match an expected value to find the
+public IP used by a user.
+.
+Hence, this package disables this feature by shipping the
+/etc/sysctl.d/tcp_timestamps.conf configuration file.
+.
+Note that TCP time stamps normally have some usefulness. They are
+needed for:
+.
+* the TCP protection against wrapped sequence numbers; however, to
+  trigger a wrap, one needs to send roughly 2^32 packets in one
+  minute:  as said in rfc 1700, "The current recommended default
+  time to live (TTL) for the Internet Protocol (IP) [45,105] is 64".
+  So, this probably won't be a practical problem in the context
+  of Anonymity Distributions.
+.
+* "Round-Trip Time Measurement", which is only useful when the user
+  manages to saturate their connection. When using Anonymity Distributions,
+  probably the limiting factor for transmission speed is rarely the capacity
+  of the user connection.
+.
+Netfilter's connection tracking helper module increases kernel attack 
+surface by enabling superfluous functionality such as IRC parsing in 
+the kernel (!)
+.
+Hence, this package disables this feature by shipping the
+/etc/sysctl.d/nf_conntrack_helper.conf configuration file.

etc/sysctl.d/nf_conntrack_helper.conf

@@ -0,0 +1 @@
+net.netfilter.nf_conntrack_helper=0

etc/sysctl.d/tcp_timestamps.conf

@@ -0,0 +1 @@
+net.ipv4.tcp_timestamps=0