APPLIED[D/Unstable]: [SRU C, D/Unstable][PATCH 0/1] netfilter: nf_conncount: fix for LP#1811094

[Seth Forshee]

On Thu, Jan 10, 2019 at 01:45:38AM -0200, Mauricio Faria de Oliveira wrote:
> BugLink: https://bugs.launchpad.net/bugs/1811094
> 
> [Note to Cosmic/Disco/Unstable]
> 
> Cosmic and later are not severely affected, as the main fix
> commit is applied.  However, there's this particular commit
> that fixes that fix which the netfilter maintainer required,
> and it's part of the Xenial/Bionic patch series, so it must
> be applied to later releases as well for consistency.
> 
> [Impact] 
> 
>  * The iptables connection count/limit rules can be breached 
>    with multithreaded network driver/server/client (common)
>    due to a race in the conncount/connlimit code.
> 
>  * For example:
> 
>    # iptables -A INPUT -p tcp -m tcp --syn --dport 7777 \
>      -m connlimit --connlimit-above 2000 --connlimit-mask 0 \
>      -j DROP
> 
>  * The fix is a backport from an upstream commit that resolves
>    the problem (plus dependencies for a cleaner backport) that
>    address the race condition:
> 
>    commit b36e4523d4d5 ("netfilter: nf_conncount: fix garbage
>    collection confirm race").
> 
> [Test Case]
> 
>  * Server-side: (relevant kernel side)
>    (limit TCP port 7777 to only 2000 connections)
> 
>    # iptables -A INPUT -p tcp -m tcp --syn --dport 7777 \
>      -m connlimit --connlimit-above 2000 --connlimit-mask 0 \
>      -j DROP
> 
>    # ulimit -SHn 65000   # increase number of open files
>    # ruby server.rb      # multi-threaded server
> 
>  * Client-side:
> 
>    # ulimit -SHn 65000
>    # ruby client.rb <server ip> <port> <target # connections> <# threads> 
>    <test output>
> 
>  * Results with Original kernel:
>    (client achieves target of 6000 connections > limit of 2000 connections)
> 
>    # ruby client.rb 10.230.56.100 7777 6000 3 
>    1
>    2
>    3
>    <...>
>    6000
>    Target reached. Thread finishing
>    6001
>    Target reached. Thread finishing
>    6002
>    Target reached. Thread finishing
>    Threads done. 6002 connections
>    press enter to exit
> 
>  * Results with Modified kernel:
>    (client is limited to 2000 connections, and times out afterward)
> 
>    # ruby client.rb 10.230.56.100 7777 6000 3
>    1
>    2
>    3
>    <...>
>    2000
>    <... blocks for a few minutes ...>
>    failed to create connection: Connection timed out - connect(2) for "10.230.56.100" port 7777
>    failed to create connection: Connection timed out - connect(2) for "10.230.56.100" port 7777
>    failed to create connection: Connection timed out - connect(2) for "10.230.56.100" port 7777
>    Threads done. 2000 connections
>    press enter to exit
> 
>  * Test cases possibly available upon request,
>    depending on original author's permission.
> 
> [Regression Potential] 
> 
>  * The patchset has been reviewed by a netfilter maintainer [1] in
>    stable mailing list, and was considered OK for 4.14, and that's
>    essentially the same backport for 4.15 and 4.4. 
> 
>  * The changes are limited to netfilter conncount/connlimit (names
>    change between older/newer kernel versions).
> 
> [Other Info]
>  
>  * The backport for 4.14 [2] is applied as of 4.14.92.
> 
> [1] https://www.spinics.net/lists/stable/msg276883.html
> [2] https://www.spinics.net/lists/stable/msg276910.html

Applied to disco/master-next and unstable/master, thanks!