🔗 Using c-icap for proxy content antivirus checking on-the-fly
by Yuri Voinov
For Squid-3.0 and later we can use ICAP for content filtering or antivirus checking. This config example describes how to scan for viruses on-the-fly using squidclamav antivirus module in combination with ClamAV antivirus service. It is a bit different with recommended squidclamav configuration and adapted for Squid-3.4 releases and above with latest configuration changes.
This will be useful both for interception and explicit proxies. With proper ClamAV configuration verification brings almost no noticeable delay and performed with acceptable latency.
🔗 Building c-icap server
Download latest c-icap sources (Changelog).For antivirus checking you do not need BerkeleyDB support. Then configure as shown below and make.
# 32 bit ./configure 'CXXFLAGS=-O2 -m32 -pipe' 'CFLAGS=-O2 -m32-pipe' --enable-large-files --without-bdb --prefix=/usr/local # 64 bit ./configure 'CXXFLAGS=-O2 -m64 -pipe' 'CFLAGS=-O2 -m64 -pipe' --without-bdb --prefix=/usr/local make/gmake make/gmake install-strip
🔗 Configuring and run c-icap server
Edit c-icap.conf as follows:
PidFile /var/run/c-icap/c-icap.pid CommandsSocket /var/run/c-icap/c-icap.ctl StartServers 1 MaxServers 20 MaxRequestsPerChild 100 Port 1344 User squid Group squid ServerAdmin yourname@yourdomain TmpDir /tmp MaxMemObject 131072 DebugLevel 0 ModulesDir /usr/local/lib/c_icap ServicesDir /usr/local/lib/c_icap LoadMagicFile /usr/local/etc/c-icap.magic acl localhost src 127.0.0.1/255.255.255.255 acl PERMIT_REQUESTS type REQMOD RESPMOD icap_access allow localhost PERMIT_REQUESTS icap_access deny all ServerLog /var/log/i-cap_server.log AccessLog /var/log/i-cap_access.log
Edit paths if necessary and start c-icap server. Add startup script to your OS.
Note: Method OPTIONS is excluding from scanning in latest squidclamav release (starting from squidclamav version 6.14). So, permit access for it not required.
Note: TmpDir usually set to /var/tmp (this is default). Be very careful when change it. TmpDir uses for temp files when oblect in memory greater than MaxMemObject. And this temp files (CI_TMP_XXXX) remains in TmpDir when processing complete. Schedule housekeeping for TmpDir otherwise free space on /var filesystem can ran out on high loaded servers.
Note: In some cases you can increase MaxMemObject to increase performance at the cost of some increase in consumption of RAM. Sometimes it is advisable to set this parameter to the maximum value of the logical IO unit for your OS.
🔗 Antivirus checking with c-icap, ClamAV daemon and Squidclamav
Of course, this installation requires more resources, especially when installing on single host. But also provides more flexibility and - in some cases - more scalability.
🔗 Build, configuring and run ClamAV daemon
ClamAV including in many repositories and can be got from them. When configuring clamd, be very conservative with options. Defaults is good starting point. I do not recommend using SafeBrowsing due to performance and memory issues and DetectPUA due to much false-positives. Also take care about antivirus databases updates - it will occurs often enough. I use 24 times per day.
Note: ClamAV daemon (clamd) is memory consumption service, it uses about 200-300 megabytes in minimal configuration (mainly used to store AV database in memory), it can be higher during deep scans of big archives. So, you can put it on separate node with fast network interconnect with your proxy (this option is valid only when using squidclamav).
Note: It is important to set StreamMaxLength parameter in clamd.conf to the same value as maxsize in squidclamav.conf.
I.e., uncomment and adjust in clamd.conf:
🔗 Build and configuring squidclamav
Installing SquidClamav requires that you already have installed the c-icap as explained above. You must provide the installation path of c-icap to the configure command as follow, compile and then install:
# 32 bit ./configure 'CXXFLAGS=-O2 -m32 -pipe' 'CFLAGS=-O2 -m32 -pipe' --with-c-icap=/usr/local # 64 bit ./configure 'CXXFLAGS=-O2 -m64 -pipe' 'CFLAGS=-O2 -m64 -pipe' --with-c-icap=/usr/local make/gmake make/gmake install-strip
this will install the squidclamav.so library into the c-icap modules/services repository. Then add the line below to the c-icap.conf file:
Service squidclamav squidclamav.so
Then adjust squidclamav.conf as follows:
and restart c-icap server. Finally don’t forget to put clwarn.cgi.xx_XX (where xx_XX matches your language) into your web server cgi-bin directory.
As whitelist can be big enough, to reduce maintenance and simplify administration you can create separate file contains whitelist regex’s and configure squidclamav as follows:
# White list some sites # Abort both AV and chained program whitelist /usr/local/etc/squidclamav_whitelist
where squidclamav_whitelist contains:
clamav\.net securiteinfo\.com sanesecurity\.com clamav\.bofhland\.org threatcenter\.crdf\.fr ...
Note: You may want to use I-CAP templates for redirection, against squidclamav redirection. In this case you must customize c-icap templates according to your needs.
🔗 Squid Configuration File
Squid-3.4 and older need to be built with the –enable-icap-client option. Newer releases have this enabled by default.
Paste the configuration file like this:
# ------------------------------------- # Adaptation parameters # ------------------------------------- icap_enable on icap_send_client_ip on icap_send_client_username on icap_client_username_header X-Authenticated-User icap_preview_enable on icap_preview_size 1024 icap_service service_avi_req reqmod_precache icap://localhost:1344/squidclamav bypass=on adaptation_access service_avi_req allow all icap_service service_avi_resp respmod_precache icap://localhost:1344/squidclamav bypass=off adaptation_access service_avi_resp allow all
IPv6-enabled operating systems may resolve localhost to the dual-stack enabled ::1 address. If you have troubles with connectivity to IPv4-only ICAP services, just replace localhost above with 127.0.0.1.
🔗 Antivirus checking with c-icap and virus checking module
Like eCAP, you can perform antivirus checking with libclamav. This not requires daemon and fries up to 500 Mbytes (average) required to run clamd. This can be useful for single-tier setups.
I-CAP modules provides two submodules: using ClamAV daemon, and using libclamav only.
🔗 Build c-icap modules
Download last modules, then configuring and build according your ClamAV and c-icap build types (32 or 64 bit):
# 32 bit GCC ./configure 'CFLAGS=-O3 -m32 -pipe' 'CPPFLAGS=-I/usr/local/clamav/include' 'LDFLAGS=-L/usr/local/lib -L/usr/local/clamav/lib' # 64 bit GCC ./configure 'CFLAGS=-O3 -m64 -pipe' 'CPPFLAGS=-I/usr/local/clamav/include' 'LDFLAGS=-L/usr/local/lib -L/usr/local/clamav/lib/' gmake gmake install-strip
To build submodule clamav_mod (uses libclamav) you can require patch your c-icap installation with last fixes. It uses OpenSSL headers dependency and you can have problems with modules build. This can be workarounded if your system has an older OpenSSL version (i.e. 0.9.8). To do that just add old OpenSSL headers path to CPPFLAGS variable.
🔗 Configuring c-icap modules
Add non-default parameters into clamav_mod.conf:
clamav_mod.TmpDir /var/tmp clamav_mod.MaxFilesInArchive 1000 clamav_mod.MaxScanSize 5M clamav_mod.HeuristicScanPrecedence on clamav_mod.OLE2BlockMacros on
Add non-default parameters into virus_scan.conf:
virus_scan.ScanFileTypes TEXT DATA EXECUTABLE ARCHIVE DOCUMENT virus_scan.SendPercentData 5 virus_scan.PassOnError on virus_scan.MaxObjectSize 5M virus_scan.DefaultEngine clamav Include clamav_mod.conf
Add following line at the end of c-icap.conf:
Note: You also must create symbolic link in ClamAV installation directory pointed to ClamAV antivirus database directory, configured for daemon in clamd.conf, for example:
# ln -s /var/lib/clamav /usr/local/clamav/share/clamav
Finally restart c-icap service to accept changes.
🔗 Squid Configuration File
Squid-3.4 needs to be built with the –enable-icap-client option. Newer releases have this enabled by default.
Paste the configuration file like this:
icap_enable on icap_service service_avi_req reqmod_precache icap://localhost:1344/virus_scan bypass=off adaptation_access service_avi_req allow all icap_service service_avi_resp respmod_precache icap://localhost:1344/virus_scan bypass=on adaptation_access service_avi_resp allow all
When using squidclamav, you must bypass whitelisted sites with Squid ACL’s and adaptation_access directives. Also you can customize virus_scan module templates to your language etc.
Also beware: without clamd you will have the same 300-500 megabytes of loaded AV database to one of c-icap process with libclamav.
🔗 Testing your installation
Point your client machine behind proxy to EICAR test virus and make sure you’re get redirected to warning page.
For really big installations you can place all checking infrastructure components on separate nodes - i.e. proxy, c-icap server, ClamAV. That’s all, folks!
🔗 DNSBL filtering support
In case of paranoia, you can also enable DNSBL URL checking support to your c-icap compatible setup.
To do this you requires to download and install c-icap modules:
# 32 bit GCC ./configure 'CFLAGS=-O3 -m32 -pipe' 'CPPFLAGS=-I/usr/local/clamav/include' 'LDFLAGS=-L/usr/local/lib -L/usr/local/clamav/lib' # 64 bit GCC ./configure 'CFLAGS=-O3 -m64 -pipe' 'CPPFLAGS=-I/usr/local/clamav/include' 'LDFLAGS=-L/usr/local/lib -L/usr/local/clamav/lib' gmake gmake install-strip
then add this to your c-icap.conf file:
Module common dnsbl_tables.so Include srv_url_check.conf
Adjust srv_url_check.conf as follows:
Service url_check srv_url_check.so url_check.LookupTableDB whitelist domain hash:/usr/local/etc/domain.whitelist "Whitelist" url_check.LookupTableDB blackuribl domain dnsbl:black.uribl.com url_check.Profile default pass whitelist url_check.Profile default block blackuribl url_check.Profile default pass ALL url_check.DefaultAction pass AddXHeader "X-Next-Services"
Note: Using whitelist is good idea for performance reasons. It is plain text file with 2nd level domain names. All hostnames beyong this domains will be pass. Also setup DNS cache is also great idea to improve performance.
and add this to your squid.conf:
# DNSBL service # Requires to enable "Module common dnsbl_tables.so" in c-icap.conf, # and install and configure c-icap modules! icap_service service_dnsbl_req reqmod_precache icap://localhost:1344/url_check bypass=on adaptation_access service_dnsbl_req allow all
Finally you must restart c-icap service and restart your squid. That’s basically all.
Note: Add DNSBL ICAP service before ClamAV antivirus service.
When using squidclamav AV service, can be better to create adaptation chain on requests, like this:
icap_enable on icap_send_client_ip on icap_send_client_username on icap_client_username_header X-Client-Username icap_preview_enable on icap_preview_size 1024 icap_service_failure_limit -1 # DNSBL service # Requires to enable "Module common dnsbl_tables.so" in c-icap.conf icap_service service_dnsbl_req reqmod_precache icap://localhost:1344/url_check bypass=on routing=on # ClamAV service icap_service service_avi_req reqmod_precache icap://localhost:1344/squidclamav bypass=on adaptation_service_chain svcRequest service_dnsbl_req service_avi_req adaptation_access svcRequest allow all icap_service service_avi_resp respmod_precache icap://localhost:1344/squidclamav adaptation_access service_avi_resp allow all
When using DNSBL, it is recommended to set up a DNS cache on the c-icap host for performance.
🔗 Performance and tuning
In practice, configuration with clamd and squidclamav is fastest. In fact, squidclamav using INSTREAM to perform AV checks is the best way. You may need only adjust the amount of the workers in the c-icap service according to your load. You will have only two bottlenecks - the interaction of your proxy server with c-icap and interaction of c-icap with antivirus service. You need to reduce latency of these interactions to the minimum possible.
In some cases, placing all services on a single host is not a good idea. High-load setups must be separated between tiers.
Do not do extra work - use white lists where possible.
Avoid overload - especially in the case of all services installed on a single host.
Reduce memory consumption as possible. Do not set high clamd system limits - these increases latency and memory consumption and can lead to a system crash during peak hours.
Use chains to adapt and customize the sequence correctly, and make correct access - so as not to overload the individual stages of unnecessary work.
c-icap workers produces high CPU load during scanning in all cases. You must minimize scanning as much as possible. Do not scan all data types. Do not scan trusted sites. And do not try to scan Youtube videos, of course.
On some Solaris setups you can get performance gain by using libmtmalloc for c-icap processes. Just add -lmtmalloc to CFLAGS and CXXFLAGS when configuring. This also can reduce memory lock contention on multi-core CPU boxes. This solution can also reduce the memory consumption problem for clamd.
Clamd with custom databases (SecuriteInfo, etc.) or latest version (0.102.x) uses 700 megabytes of RAM and above. Better in this case to use separate servers.
🔗 Multi-tier setups
Due to last ClamAV utilizes a lot of memory (up to 1 Gb RAM), multi-tier setups can be better.
To build this, keep in mind:
c-icap should remain on squid’s tier; due to squid connectivity with c-icap over TCP is non-reliable.
squidclamav will talk with clamd via TCP; just modify squidclamav.conf and restart c-icap:
clamd_ip your_clamav_tier_ip clamd_port 3310
Comment out clamd_local in squidclamav.conf.
On ClamAV tier uncomment this parameter in clamd.conf and restart daemon:
Don’t forget to open TCP port 3310 on ClamAV tier firewall.
🔗 C-ICAP monitoring
To monitor some runtime statistics from C-ICAP, you can use solution, as described here with some additions and corrections.
You can use both CLI and web interface to monitor C-ICAP via built-in info service.
To use CLI, use this command (or add it as shell alias):
/usr/local/bin/c-icap-client -s "info?view=text" -i localhost -p 1344 -req use-any-url
or, as shell alias:
alias icap_stat='c-icap-client -s '\''info?view=text'\'' -i localhost -p 1344 -req use-any-url'
The result will looks as shown:
ICAP server:localhost, ip:127.0.0.1, port:1344 Running Servers Statistics =========================== Children number: 3 Free Servers: 27 Used Servers: 3 Started Processes: 5 Closed Processes: 2 Crashed Processes: 2 Closing Processes: 0 Child pids: 24689 15427 4947 Closing children pids: Semaphores in use sysv:accept/4 sysv:children-queue/5 Shared mem blocks in use sysv:kids-queue/30 13 kbs General Statistics ================== REQUESTS : 44501 REQMODS : 39336 RESPMODS : 5071 OPTIONS : 94 FAILED REQUESTS : 5 ALLOW 204 : 44245 BYTES IN : 25625 Kbs 486 bytes BYTES OUT : 5679 Kbs 536 bytes HTTP BYTES IN : 16232 Kbs 612 bytes HTTP BYTES OUT : 212 Kbs 887 bytes BODY BYTES IN : 2621 Kbs 532 bytes BODY BYTES OUT : 192 Kbs 288 bytes
To get same info via web, just add this lines in squid.conf and reconfigure:
# ICAP info service. URL: http://icap.info acl infoaccess dstdomain icap.info icap_service service_info reqmod_precache 1 icap://localhost:1344/info adaptation_service_set class_info service_info adaptation_access class_info allow infoaccess adaptation_access class_info deny all
Use url above to access stats page.
Here is also Munin plugins for C-ICAP monitoring (performance-related /runtime stats):
When upgrading c-icap server, you also need (in most cases) to rebuild squidclamav to aviod possible API incompatibility.
In case of c-icap permanently restarts, increase DebugLevel in c-icap.conf and check ServerLog first. Beware, DebugLevel 0 is production value, which can mask any problems during tune up.
🔗 c-icap/eCAP co-existance
To apply multiple adaptation services to the same transaction at the same vectoring point, one must use adaptation_service_chain. Adaptation order is often important from adaptation logic or performance point of view, but Squid supports any order of chained services. Squid adaptation chaining code does not even know the difference between ICAP and eCAP! For example, an adaptation_service_chain containing an ICAP service followed by an eCAP service, followed by another ICAP service is supported.
When you require both c-icap and eCAP in one Squid’s instance, you must remember: order of adaptation service/chain definitions and adaptation_access ACL’s is important. Adaptation logic defines in adaptation service default order of preference, in adaptation_access directives define which services or chains are able to be used for the transaction being considered. In some cases, adaptation actions chain can be mutually exclusive. So, be careful with adaptation configuration. Thoroughly test adaptation logic.
Note: The simplest case is to chain adaptations with the same access scheme. When access scheme is different for chained adaptations, use adaptation_access in correct sequence to achieve required adaptation goals.
⚠️ Disclaimer: Any example presented here is provided "as-is" with no support or guarantee of suitability. If you have any further questions about these examples please email the squid-users mailing list.
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