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abanoub
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Joined: 25 Apr 2022
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Location: Mount Olympus
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 Posted: Thu Jul 21, 2022 1:06 pm Post subject: SELinux : "avc: denied" message spamming my dmesg |
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Title says it all, when booting (and after boot too) my dmesg is spammed of "avc: denied" messages like this:
| Code: | | [ 893.531060] audit: type=1400 audit(1658408460.688:929): avc: denied { use } for pid=8792 comm="sh" path="/dev/tty1" dev="devtmpfs" ino=20 ioctlcmd=0x540f scontext=staff_u:sysadm_r:sysadm_t tcontext=system_u:system_r:kernel_t tclass=fd permissive=1 |
But even with these messages, my system still boots fine.
Anyways thanks in advance, I'm sorry if I'm forgetting any crucial logs or whatever as I'm new to SELinux.
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Last edited by abanoub on Thu Jul 21, 2022 8:21 pm; edited 2 times in total |
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pjp
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Joined: 16 Apr 2002
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| Posted: Thu Jul 21, 2022 1:22 pm Post subject: |
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Is SELinux configured to enforce? SELinux state and mode
How to read and correct SELinux denial messages (RedHat) seems to have some good information. If nothing else, maybe you can get the "more approachable" messages.
I haven't read Gentoo's SELinux wiki closely, but at first glance, it seems to have some resources that may be helpful.
So far I've only looked into SELinux sufficiently to determine that it isn't practical to retrofit onto an existing environment. At least not where implementing it isn't a priority.
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abanoub
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Location: Mount Olympus
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| Posted: Thu Jul 21, 2022 1:35 pm Post subject: |
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| pjp wrote: | | Is SELinux configured to enforce? |
No its configured to permissive.
| pjp wrote: | | How to read and correct SE Linux denial messages (RedHat) seems to have some good information. If nothing else, maybe you can get the "more approachable" messages. |
Thanks, will give that a read.
| pjp wrote: | | I haven't read Gentoo's SE Linux wiki closely, but at first glance, it seems to have some resources that may be helpful. |
EDIT: Looking at that link you sent about SE Linux modes, I see that the easiest way to stop the kernel error messages is to just disable SE Linux because by setting it to enforce it'll actually start causing problems as a lot of the errors I'm getting are for essential system stuff, but that's not practical since at that point that would just be extra bloat by leaving it in and not using it, and plus I'd have to choose another profile and all that.
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pjp
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| Posted: Thu Jul 21, 2022 5:22 pm Post subject: |
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Verifying the mode setting was to clarify "But even with these messages, my system still boots fine. "
It (may) boot fine because the configuration is set to permissive. As you point out, if you were to enable enforcing mode, it would likely cause problems.
One approach to configuring SELinux is to use permissive mode and create the rules from the messages. The RH link mentioned "more approachable" messages, which (may?) provide better information about what to configure to allow whatever caused the error.
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abanoub
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| Posted: Thu Jul 21, 2022 8:20 pm Post subject: |
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| pjp wrote: | | One approach to configuring SE-Linux is to use permissive mode and create the rules from the messages. The RH link mentioned "more approachable" messages, which (may?) provide better information about what to configure to allow whatever caused the error |
Yeah, about this my "solution" was to just switch out my hardened/SE-Linux profile since its caused more problems if anything and hasn't increased my security 1 bit.
Still, thanks for your help man.
And about the RH link, I've checked in the directories it mentions and suprise suprise there are no logs at all.
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pjp
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| Posted: Thu Jul 21, 2022 10:25 pm Post subject: |
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You're welcome, such as it was. Reaching a decision is always nice too :). Hardening is definitely a challenge, especially with "desktop" type environments.
In case anyone comes along, I'll add a couple of clarifying quotes from the RH link | Quote: | Where are denials logged?
Now, these AVC denials, much like everything else in Linux, are logged by the system. Where those messages are logged varies depending on which system daemons are running.
auditd on - /var/log/audit/audit.log
auditd off; rsyslogd on - /var/log/messages
setroubleshootd, rsyslogd, and auditd on - Both locations, though the messages in /var/log/messages are easier to make sense of |
| Quote: | Here the output is in more approachable language, and if you read carefully, a solution is presented:
Sep 22 13:35:24 server setroubleshoot[3999]: SELinux is preventing rhsmcertd-worke from read access on the file virt.module. For complete SELinux messages run: sealert -l 97a1c0df-81ed-4c08-ba27-41c5067b713b
Sep 22 13:35:24 server platform-python[3999]: SELinux is preventing rhsmcertd-worke from read access on the file virt.module.#012#012***** Plugin catchall_boolean (89.3 confidence) suggests ******************#012#012If you want to allow daemons to dump core#012Then you must tell SELinux about this by enabling the 'daemons_dump_core' boolean.#012#012Do#012setsebool -P daemons_dump_core 1#012#012***** Plugin catchall (11.6 confidence) suggests **************************#012#012If you believe that rhsmcertd-worke should be allowed read access on the virt.module file by default.#012Then you should report this as a bug.#012You can generate a local policy module to allow this access.#012Do#012allow this access for now by executing:#012# ausearch -c 'rhsmcertd-worke' --raw | audit2allow -M my-rhsmcertdworke#012# semodule -X 300 -i my-rhsmcertdworke.pp#012 |
I'm guessing setroubleshootd would need to be configured (and possibly other things) to log the "approachable" messages. Also, auditd likely comes from sys-process/audit. And since Gentoo isn't RH, things may not be the same.
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