On 08/11/17 12:18, A. Benz wrote:
Hi all,
## Intro
I read many blogs and emails on this list related to what I'm trying to
do, but most go into bumping or do things that are not as simple as I'm
trying to achieve.
I have an extremely slow line, with very high latency in a remote
location. About 14 people are sharing this line. Nowadays with all the
mobile apps trying to sync and such, the line stalls to unusable all the
time.
I tried doing filters with firewall or dns level, but those are not
effective. In the end I figured squid might be my best option.
## End intro
I have squid 3.5.27 running under LEDE (OpenWrt fork), ie its
cross-compiled for a MIPS based SoC (mediatek mt7621). I mention this
because you will see some options in the config file that won't make
sense otherwise.
NP: That should not be making much difference to the squid.conf
settings. The worst limitations such devices impose are things that
should be solved by OS settings outside of squid.conf. eg the cache.log
going to a pipe for remote logging instead of a filename, and
system-level FD limits.
It works great, here's what I'm trying to achieve: Allow access only to
a pre-defined list of websites (whitelist). http is straightforward, but
if the connection is https all I need to know is domain, if its allowed,
let it pass, otherwise terminate.
this setup is working as intended with the config attached below,
however the issue I'm facing is that some servers are "loadbalanced",
this would give me the forgery error, eg:
"SECURITY ALERT: Host header forgery detected on...."
The workarounds and gotcha's listed at
<https://wiki.squid-cache.org/KnowledgeBase/HostHeaderForgery> are the
best you can hope for there. The most successful all-round solution is
to increase EDNS0 capabilities.
Here's a specific example, there's a corporate domain for webmail
access, and some loadbalance config makes use of different IPs, I think
this is what triggers the error. My question is, can I just ignore this
error somehow and allow the connection? From what I gather this
connection is cut by squid before it reaches the client..
Squid default behaviour is to allow the connection only to the same
IP:port the client was connecting to. If that is not working your
network configuration is screwed up. Specifically your routing or NAT.
NAT of the dst-IP:port *MUST NOT* happen on any device between the
client machine and the proxy machine. Squid needs access directly to the
kernel NAT records of the device doing that NAT operation. So it can
only happen on the Squid device.
You must *route* the packets unchanged to the Squid device (possibly
over a tunnel if necessary).
Also if there's anything else obviously wrong with my setup please let
me know.
Many thanks.
Here's my config:
### squid.conf begin
acl localnet src 10.0.0.0/8
acl localnet src 172.16.0.0/12
acl localnet src 192.168.0.0/16
acl ssl_ports port 443
acl safe_ports port 80
acl safe_ports port 443
acl connect method connect
NP: the default above ACL names are case-sensitive and some of them
involve built-in default values which you are preventing having any
effect by using custom lower-case ACL names.
acl http_whitelist dstdomain "/etc/squid/whitelist.txt"
acl https_whitelist ssl::server_name "/etc/squid/whitelist.txt"
acl ips_whitelist dst "/etc/squid/ips.txt"
http_port 3128 intercept
http_port 3129
Port 3128 is registered for forward-proxy traffic. Ideally you would
have those lines reversed like so:
http_port 3128
http_port 3129 intercept
... with the corresponding NAT change for the intercept port.
Also, to have your SSL-Bump whitelists applied to forward-proxy CONNECT
traffic you should have ssl-bump settings on that 3128 forward-proxy
port matching those on the port 3130 line.
http_access deny !safe_ports
http_access deny connect !ssl_ports
http_access allow ssl_ports
Rather than allowing unlimited access to anyone on the Internet to use
your limited bandwidth outbound connection for access to port 443 you
should be using the localnet ACL that restricts use of the proxy to
people on your LAN - those 14 clients you mentioned sharing the line.
[NP: It is not possible in this setup to determine what remote users are
abusing your proxy. All traffic logs from your firewall etc will show
Squid as the client, not the remote [ab]user. Squid access.log records
you are sending to /dev/null is the *only* record of such activities.]
To make your whitelists have any effect replace the above "allow
ssl_ports" line with a "deny !localnet" line.
If that change causes issues then your whitelists are incorrect /
incomplete. You then need the (currently discarded) access.log and/or
cache.log data to solve the issue properly.
http_access allow http_whitelist
http_access allow ips_whitelist
http_access deny all
https_port 3130 intercept ssl-bump \
cert=/etc/squid/myCA.pem \
generate-host-certificates=off dynamic_cert_mem_cache_size=4MB
acl step1 at_step SslBump1
acl step2 at_step SslBump2
acl step3 at_step SslBump3
ssl_bump peek step1 all
ssl_bump splice https_whitelist
ssl_bump splice ips_whitelist
ssl_bump terminate all
That seems fine. The problem is not part of this _config_. If you are
having any SSL-Bump issues please try a build of the latest Squid-4. It
may be related to bugs in Squid-3 SSL-Bump or modern TLS things Squid-3
cannot cope with - there is a growing list of those.
cache deny all
In the latest Squid-3 use "store_miss deny all" instead of the above.
access_log none
The above is fine if you are certain of the squid.conf working 100%
properly. But since you are debugging issues you may need those
transaction details.
NP: access.log can be logged to syslog or a TCP pipe by Squid. To
deliver the log content externally for normal audit purposes instead of
using space on the device.
cache_log /dev/null
You *need* the information logged here. By default only the most
operationally critical errors are recorded.
NP: the cache.log can usually be a Unix-pipe delivering data to a remote
server if the local machine is constrained.
cache_store_log stdio:/dev/null
Above line is *actively* harmful. The Squid-3 default is not to waste
cycles logging *unless* you enter something like the above in
squid.conf. The above makes Squid allocate device resources to logging
that data to /dev/null.
logfile_rotate 0
logfile_daemon /dev/null
/dev/null is not a valid application filename.
Build your Squid with --disable-logfile-daemon.
coredump_dir /tmp/squid
visible_hostname main_Firewall
The *visible* hostname is the domain delivered to clients and denied
parties in the URLs to fetch error message data and FTP icons from
Squid. It needs to be a valid FQDN.
Amos
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