[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]

Re: How do I figure out on what file dac_override is attempted?



On 01/19/2010 09:52 AM, Stephen Smalley wrote:
> On Mon, 2010-01-18 at 22:05 +0100, Göran Uddeborg wrote:
>> Here is another strange AVC I'm trying to understand.
>>
>> SETroubleshoot on one of my machines is telling me that
>>
>>   SELinux is preventing plymouthd (plymouthd_t) "dac_override" plymouthd_t.
>>
>> The full message is attached.
>>
>> If I have understood this correctly, this means that plymouthd was
>> trying to read a file as root.  But the regular permissions bits of
>> the file would not allow that.  (Right?)
>>
>> I assume there is some file with wrong permission bits, which causes
>> this to happen.  But I can't find any indication WHAT file it was.
>> Looking at the message, it seems to me it was trying a dac_override on
>> itself.
>>
>> Is there a way to know what file was involved?
> 
> The capability checks in Linux do not pass the object to the security
> module, so SELinux only knows about the current task and the particular
> capability requested.  To get object information, you need to enable
> syscall auditing, and add a trivial syscall filter to turn on pathname
> collection by the audit subsystem.  Then re-try the operation that
> generated the denial.
> 
> auditctl -s
> will show the current status of the audit system.
> 
> auditctl -a exit,always -S chroot
> is an example syscall filter.
> 
> The filter doesn't need to have anything to do with your failing
> operation - it just turns on the machinery that will cause pathname
> collection so that when the AVC is generated, you will also get a
> SYSCALL record with the pathname info.
> 
So there is no easy way in the kernel to get this information into the AVC without taking the overhead hit of 
full path auditing.

> The capability checks in Linux do not pass the object to the security
> module, so SELinux only knows about the current task and the particular
> capability requested.

Would this be insanity to ask that the object be passed to the capability check?


[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]