Is this really supposed to get easier over time? :) Now my audit.log file shows that SELinux is blocking my cgi script, index.cgi (which is what's actually served when the user visits the front page of one of our proxy sites like sugarsurfer.com) from having '"read write" to socket (httpd_t)'. I have no idea what that means, except that I thought that cgi scripts were supposed to be able to write to stdout so that the web server could send the data via a socket connection to the end user's browser, so I don't know why a CGI script would be blocked from writing to a socket with security context httpd_t.
The only clue that might narrow it down is the line "Target Objects socket [ udp_socket ]". The sockets that the cgi scripts usually send output to are of course tcp sockets, so why would it say udp? The only time one of my cgi scripts might use udp would be if it were doing a hostname lookup via dns, but the index.cgi script doesn't do that at any point.
What would the pros do at this point?
***
Summary:
SELinux is preventing index.cgi (httpd_sys_script_t) "read write" to socket (httpd_t).
Detailed Description:
[SELinux is in permissive mode, the operation would have been denied but was permitted due to permissive mode.]
SELinux denied access requested by index.cgi. It is not expected that this access is required by index.cgi and this access may signal an intrusion attempt. It is also possible that the specific version or configuration of the application is causing it to require additional access.
Allowing Access:
You can generate a local policy module to allow this access - see FAQ (http://fedora.redhat.com/docs/selinux-faq-fc5/#id2961385) Or you can disable SELinux protection altogether. Disabling SELinux protection is not recommended. Please file a bug report (http://bugzilla.redhat.com/bugzilla/enter_bug.cgi) against this package.
Additional Information:
Source Context system_u:system_r:httpd_sys_script_t Target Context system_u:system_r:httpd_t Target Objects socket [ udp_socket ] Source index.cgi Source Path <Unknown> Port <Unknown> Host <Unknown> Source RPM Packages Target RPM Packages Policy RPM selinux-policy-2.4.6-316.el5 Selinux Enabled True Policy Type targeted MLS Enabled True Enforcing Mode Permissive Plugin Name catchall Host Name g6950-21025.securedservers.com Platform Linux g6950-21025.securedservers.com 2.6.18-274.12.1.el5 #1 SMP Tue Nov 29 13:37:46 EST 2011 x86_64 x86_64 Alert Count 1 First Seen Wed Jan 11 09:34:13 2012 Last Seen Wed Jan 11 09:34:13 2012 Local ID 2adcd43d-7b8b-4e17-bb93-ad11a35f378a Line Numbers 1
Raw Audit Messages
type=AVC msg=audit(1326303253.473:3626): avc: denied { read write } for pid=6668 comm="index.cgi" path="socket:[415055]" dev=sockfs ino=415055 scontext=system_u:system_r:httpd_sys_script_t:s0 tcontext=system_u:system_r:httpd_t:s0 tclass=udp_socket
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On 01/11/2012 01:18 PM, Bennett Haselton wrote:
Is this really supposed to get easier over time? :) Now my audit.log file shows that SELinux is blocking my cgi script, index.cgi (which is what's actually served when the user visits the front page of one of our proxy sites like sugarsurfer.com) from having '"read write" to socket (httpd_t)'. I have no idea what that means, except that I thought that cgi scripts were supposed to be able to write to stdout so that the web server could send the data via a socket connection to the end user's browser, so I don't know why a CGI script would be blocked from writing to a socket with security context httpd_t.
The only clue that might narrow it down is the line "Target Objects socket [ udp_socket ]". The sockets that the cgi scripts usually send output to are of course tcp sockets, so why would it say udp? The only time one of my cgi scripts might use udp would be if it were doing a hostname lookup via dns, but the index.cgi script doesn't do that at any point.
What would the pros do at this point?
Summary:
SELinux is preventing index.cgi (httpd_sys_script_t) "read write" to socket (httpd_t).
Detailed Description:
[SELinux is in permissive mode, the operation would have been denied but was permitted due to permissive mode.]
SELinux denied access requested by index.cgi. It is not expected that this access is required by index.cgi and this access may signal an intrusion attempt. It is also possible that the specific version or configuration of the application is causing it to require additional access.
Allowing Access:
You can generate a local policy module to allow this access - see FAQ (http://fedora.redhat.com/docs/selinux-faq-fc5/#id2961385) Or you can disable SELinux protection altogether. Disabling SELinux protection is not recommended. Please file a bug report (http://bugzilla.redhat.com/bugzilla/enter_bug.cgi) against this package.
Additional Information:
Source Context system_u:system_r:httpd_sys_script_t Target Context system_u:system_r:httpd_t Target Objects socket [ udp_socket ] Source index.cgi Source Path <Unknown> Port <Unknown> Host <Unknown> Source RPM Packages Target RPM Packages Policy RPM selinux-policy-2.4.6-316.el5 Selinux Enabled True Policy Type targeted MLS Enabled True Enforcing Mode Permissive Plugin Name catchall Host Name g6950-21025.securedservers.com Platform Linux g6950-21025.securedservers.com 2.6.18-274.12.1.el5 #1 SMP Tue Nov 29 13:37:46 EST 2011 x86_64 x86_64 Alert Count 1 First Seen Wed Jan 11 09:34:13 2012 Last Seen Wed Jan 11 09:34:13 2012 Local ID 2adcd43d-7b8b-4e17-bb93-ad11a35f378a Line Numbers 1
Raw Audit Messages
type=AVC msg=audit(1326303253.473:3626): avc: denied { read write } for pid=6668 comm="index.cgi" path="socket:[415055]" dev=sockfs ino=415055 scontext=system_u:system_r:httpd_sys_script_t:s0 tcontext=system_u:system_r:httpd_t:s0 tclass=udp_socket
_______________________________________________ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
Looks like a leaked file descriptor, you can probably add a dontaudit rule.
In Fedora we currently dontaudit this leak.
audit2allow -i /tmp/t
#============= httpd_sys_script_t ============== #!!!! This avc has a dontaudit rule in the current policy
allow httpd_sys_script_t httpd_t:udp_socket { read write };
On 01/12/2012 03:48 AM, Daniel J Walsh wrote:
In Fedora we currently dontaudit this leak.
audit2allow -i /tmp/t
#============= httpd_sys_script_t ============== #!!!! This avc has a dontaudit rule in the current policy
allow httpd_sys_script_t httpd_t:udp_socket { read write };
Pow. Reasonable answer, and it isn't so hard to run that command -- its just difficult to understand why its necessary if you don't know anything about the environment, and mystifying if you know the command but nothing about what's going on.
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On 01/11/2012 02:50 PM, 夜神 岩男 wrote:
On 01/12/2012 03:48 AM, Daniel J Walsh wrote:
In Fedora we currently dontaudit this leak.
audit2allow -i /tmp/t
#============= httpd_sys_script_t ============== #!!!! This avc has a dontaudit rule in the current policy
allow httpd_sys_script_t httpd_t:udp_socket { read write };
Pow. Reasonable answer, and it isn't so hard to run that command -- its just difficult to understand why its necessary if you don't know anything about the environment, and mystifying if you know the command but nothing about what's going on. _______________________________________________ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
The following explaines leaked file descriptors.
http://danwalsh.livejournal.com/6117.html?thread=23525
In RHEL6 and Fedora you can run avc messages through audit2allow and it will tell you whether or not there is policy effecting the AVC.
setroubleshoot can also be helpful in these circumstances.
On 01/12/2012 03:18 AM, Bennett Haselton wrote:
Is this really supposed to get easier over time? :) Now my audit.log file shows that SELinux is blocking my cgi script, index.cgi (which is what's actually served when the user visits the front page of one of our proxy sites like sugarsurfer.com) from having '"read write" to socket (httpd_t)'. I have no idea what that means, except that I thought that cgi scripts were supposed to be able to write to stdout so that the web server could send the data via a socket connection to the end user's browser, so I don't know why a CGI script would be blocked from writing to a socket with security context httpd_t.
Your cgi script isn't allowed to write to the socket file. The context httpd_t isn't touchable by your executable. Is your index.cgi script custom or something from a distro package?
In any case you can find a way to deliberately make this audit message show up (sounds like you have), try to vary it a few times to get a good base of audit information, and then use audit2allow to inspect the last several lines of your audit file.
From this you can have audit2allow create and package a new policy that explicitely permits just this access and nothing else. See if you get any more AVC denials (9 out of 10 times this will be the end of it). If no more AVC notices and everything works well, turn SELinux back to enforcing and test a bit.
Usually for custom scripts (of any depth, really) this is all that's needed.
I have to do the same thing every time I decide to do something weird like run a new version of Django on top of Postgres 9.1 from source with all my other custom database-using apps asking for things from other servers, etc. Even with that much messaging going around its pretty easy to pin the situation down.
You will need policycoreutils-python installed and you'll want to read over the manpages for audit2allow and any other tool that you find interesting, but its pretty easy now that you've got sane output to go by, know where/what your audit file is, and what a security context is.
The only clue that might narrow it down is the line "Target Objects socket [ udp_socket ]". The sockets that the cgi scripts usually send output to are of course tcp sockets, so why would it say udp? The only time one of my cgi scripts might use udp would be if it were doing a hostname lookup via dns, but the index.cgi script doesn't do that at any point.
No idea why it would need to talk to a UDP socket if you're absolutely certain that it doesn't need to, but it could be something else related that needs to do a lookup (Apache set to resolve names for logs, for example?).
What would the pros do at this point?
Aside from checking the policy that the audit tools come up with, it would be reasonable to run a test on the script in a clean environment (minimal install of the OS with just enough web server (Apache) setup to let the script execute) and see what is happening in the audit log (and anywhere else you're curious about -- database, other processes, file system acces, etc.).
If you're really paranoid (and a pro is paid to be, so...) it would be good to check the contents of the packets being passed in and out of the test environment to make sure you fully understand what is expected, then compare that against what you see coming from the production server.
In *any* case, putting together a quick SELinux policy that let's your app run and lets you turn SELinux back on is better in the interim than simply letting the system sit with a permissive policy while you do your homework.
-
Bennett Haselton -
Daniel J Walsh -
夜神 岩男