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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
>>>> --
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>>>> selinux@xxxxxxxxxxxxxxxxxxxxxxx
>>>> 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 };
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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>>
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