Issues logging into to more than one system

Wed Dec 8 09:53:47 UTC 2010

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On 12/08/2010 09:57 AM, Dominick Grift wrote:
> On 12/08/2010 04:06 AM, David Highley wrote:
>> "Dominick Grift wrote:"
>>>
>> On 12/05/2010 09:09 PM, David Highley wrote:
>>>>> Keep getting AVC's when I log into multiple Fedora 14 systems with
>>>>> automounted home directories. Labels keep getting mucked up after
>>>>> logging into a client NFS host.
>>>>>
>>>>> NFS directory server has files located in /export/home/<user>. Have done
>>>>> semanage fcontext -a -e /home /export/home. They automount to
>>>>> /home/<user>.
>>>>>
>>>>> time->Sat Dec  4 15:36:14 2010
>>>>> type=SYSCALL msg=audit(1291505774.397:17149): arch=c000003e syscall=21
>>>>> success=no exit=-13 a0=2320f80 a1=6 a2=20 a3=0 items=0 ppid=23814
>>>>> pid=23980 auid=1000 uid=1000 gid=1000 euid=1000 suid=1000 fsuid=1000
>>>>> egid=1000 sgid=1000 fsgid=1000 tty=(none) ses=2462
>>>>> comm="gdm-session-wor" exe="/usr/libexec/gdm-session-worker"
>>>>> subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 key=(null)
>>>>> type=AVC msg=audit(1291505774.397:17149): avc:  denied  { write } for
>>>>> pid=23980 comm="gdm-session-wor" name=".xsession-errors" dev=dm-2
>>>>> ino=392531 scontext=system_u:system_r:xdm_t:s0-s0:c0.c1023
>>>>> tcontext=system_u:object_r:user_home_t:s0 tclass=file
>>>>> ----
>>>>> time->Sat Dec  4 15:36:14 2010
>>>>> type=SYSCALL msg=audit(1291505774.397:17150): arch=c000003e syscall=77
>>>>> success=no exit=-13 a0=c a1=0 a2=7fff53028020 a3=0 items=0 ppid=23814
>>>>> pid=23980 auid=1000 uid=1000 gid=1000 euid=1000 suid=1000 fsuid=1000
>>>>> egid=1000 sgid=1000 fsgid=1000 tty=(none) ses=2462
>>>>> comm="gdm-session-wor" exe="/usr/libexec/gdm-session-worker"
>>>>> subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 key=(null)
>>>>> type=AVC msg=audit(1291505774.397:17150): avc:  denied  { write } for
>>>>> pid=23980 comm="gdm-session-wor" name=".xsession-errors" dev=dm-2
>>>>> ino=392531 scontext=system_u:system_r:xdm_t:s0-s0:c0.c1023
>>>>> tcontext=system_u:object_r:user_home_t:s0 tclass=file
>>>>> --
>>>>> selinux mailing list
>>>>> selinux at lists.fedoraproject.org
>>>>> https://admin.fedoraproject.org/mailman/listinfo/selinux
> 
>> Looks like for some reason the ~/.xsession-errors file is mislabeled.
>> it should have been type xdm_home_t instead of user_home_t.
> 
>>> Agree it should be labeled as xdm_home_t.
> 
> I guess in this case it should be labeled nfs_t.
> 
> 
>> It seems that gdm itself did not create it but that instead some program
>> that runs in the user domain created it.
> 
>> You should first try to reproduce this issue by removing the file and
>> see if this file gets created again with type user_home_t in enforcing mode.
> 
>>> Remove the file and then logged back into the NFS server and the file is
>>> recreated with the proper label.
> 
>> When this is verified, you should see if you have a file context
>> specification for ~/.xsession-errors:
> 
>>>>> $ matchpathcon ~/.xsession-errors
>>>>> /root/.xsession-errors	staff_u:object_r:xdm_home_t:s0
> 
> 
>>> Verified using matchpatchcon as above.
> 
>>> Now log into an NFS client host and get the following:
>>> ls -Z .xsession-errors
>>> -rw-------. dhighley staff system_u:object_r:nfs_t:s0 .xsession-errors
> 
>>> ls -Zd /home/dhighley
>>> drwxr-x---. dhighley staff system_u:object_r:nfs_t:s0 /home/dhighley
> 
>>> ls -Zd /home
>>> drwxr-xr-x. root root system_u:object_r:autofs_t:s0    /home
> 
>>> Note: from above that the label for .xsession-errors is now incorrect. I
>>> would submitt that the Gnome/X11 session start is mucking the file
>>> label.
> 
> It could be restorecond -u messing with it, try disabling restorecond -u
> in your gnome-session(s) and try reproduce it again (system >
> preferences > startup applications > File context maintainer (off)
> 
>> use the path to your unprivileged user home directory instead of /root
>> in my example.
> 
>> If it is verified that something running in the user domain is creating
>> the .xsession-errors file, then we must figure out what and why.
> 
>> We can do that by loading a "auditallow" rule. for example:
> 
>> mkdir ~/mytest; cd ~/mytest; echo "policy_module(mytest,1.0.0)
>> gen_require(\` attribute domain; type user_home_t; ') allow domain
>> user_home_t:file create;" > mytest.te;
> 
>>> Created and installed the policy on the NFS client system.
> 
>> make -f /usr/share/selinux/devel/Makefile mytest.pp
>> sudo semodule -i mytest.pp
> 
>> (after reproducing testing remove the installed module:
>> sudo semodule -r mytest)
> 
>> (not this may cause many avc granted messages in audit.log)
> 
>>> Reviewing audit log on client system I only see the following logged:
>>> type=USER_AUTH msg=audit(1291776422.987:31974): user pid=16805 uid=0
>>> auid=4294967295 ses=4294967295 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='op=PAM:auth entication acct="dhighley" exe="/usr/libexec/gdm-session-worker" hostname=? addr =? terminal=:0 res=failed'
>>> type=USER_LOGIN msg=audit(1291776422.990:31975): user pid=16805 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='uid=1000: exe="/usr/libexec/gdm-session-worker" hostname=? addr=? terminal=/dev/tty7 res=failed'
>>> type=USER_AUTH msg=audit(1291776434.310:31976): user pid=16804 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='op=PAM:authentication acct="dhighley" exe="/usr/libexec/gdm-session-worker" hostname=? addr=? terminal=:0 res=success'
>>> type=USER_ACCT msg=audit(1291776434.323:31977): user pid=16804 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='op=PAM:accounting acct="dhighley" exe="/usr/libexec/gdm-session-worker" hostname=? addr=? terminal=:0 res=success'
>>> type=CRED_ACQ msg=audit(1291776434.350:31978): user pid=16804 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='op=PAM:setcred acct="dhighley" exe="/usr/libexec/gdm-session-worker" hostname=? addr=? terminal=:0 res=success'
>>> type=LOGIN msg=audit(1291776434.358:31979): login pid=16804 uid=0 old auid=4294967295 new auid=1000 old ses=4294967295 new ses=72 type=USER_ROLE_CHANGE msg=audit(1291776434.501:31980): user pid=16804 uid=0 auid=1000 ses=72 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='pam: default-context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 selected-context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023: exe="/usr/libexec/gdm-session-worker" hostname=? addr=? terminal=? res=success'
>>> type=USER_START msg=audit(1291776434.593:31981): user pid=16804 uid=0 auid=1000 ses=72 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='op=PAM:session_open acct="dhighley" exe="/usr/libexec/gdm-session-worker" hostname=? addr=? terminal=:0 res=success'
>>> type=USER_LOGIN msg=audit(1291776434.595:31982): user pid=16804 uid=0 auid=1000 ses=72 subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 msg='uid=1000: exe="/usr/libexec/gdm-session-worker" hostname=? addr=? terminal=/dev/tty7 res=success'
> 
>> Now you should remove the ~/.xsession-errors file again and reproduce
>> the creation of it. Once it is recreated, search
>> /var/log/audit/audit.log for avcgrants regarding xsession-errors:
> 
>> cat /var/log/audit/audit.log | grep -i grant | grep xsession
> 
>>> Found none. But oddly this time I see:
>>> ls -Z .xsession-errors
>>> -rw-------. dhighley staff system_u:object_r:user_home_t:s0 .xsession-errors
> 
> i guess the rule in mytest.te is not broad enough; We can make it a bit
> broader by adding:
> 
> gen_require(`
> attribute userdomain;
> type user_home_dir_t;
> ')
> 
> allow userdomain { user_home_t user_home_dir_t }:{ dir file } {
> relabelto relabelfrom create read write };

Whoops! abviously make that auditallow instead of allow:

auditallow userdomain { user_home_t user_home_dir_t }:{ dir file } {
relabelto relabelfrom create read write };

(but chances are that restorecond -u just reset the context of
~/.xsession-errors, so try disabling restorecond -u first)

> and then rebuild the mytest module and reinstall it.
> 
>> That avc denial may expose some information as to which program creates
>> it, Then a solution can be considered.
> 
>> Basically a few options:
> 
>> 1. file was somehow just mislabled (cannot reproduce)
>> 2. file gets created by some application running in the user domain:
>> 2. a. can we confine this application and make it create the file with
>> type xdm_home_t instead so that xdm_t can interact with it?
>> 2. b. if all else fails, we can consider allowing xdm access to
>> user_home_t typed files.
>> 3. are we missing a boolean that can be toggled to allow this access
>> (pipe avc denial into audit2why/ use sesearch to see if there are rules
>> in the policy database that permit this access.
> 
>>> We do have use_nfs_home_dirs --> on
> 
>> 4. is something misconfigured?
>> 5. is something buggy?
>> 6. is this some kind of intrusion attempt?
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