On 04/19/2016 10:47 AM, Stephen Smalley wrote:
> On 04/19/2016 10:32 AM, YongQin Liu wrote:
>> Hi, ALL
>>
>> I am trying the android-n-preview with kernel4.4, and found the tracefs
>> is automatically mounted there by kernel, mount options like this:
>> tracefs on /sys/kernel/debug/tracing type tracefs (rw,relatime)
>>
>> And I found avc warnings on the console like this:
>> [    6.840279] init: SELinux: Could not set context for
>> /sys/kernel/debug/tracing/set_event_pid:  Operation not supported on
>> transport endpoint
>>
>> I think it's caused by the following lines in file_contexts file:
>> /sys/kernel/debug/tracing(/.*)?          u:object_r:debugfs_tracing:s0
>> /sys/kernel/debug/tracing/trace_marker   u:object_r:debugfs_trace_marker:s0
>>
>>
>> And seems the tracefs does not support the seclabel mount option,
>>
>> So what's the better way to support tracefs in Android?
>> Seems updating sepolicy rules is an easier way, but what if the kernel
>> still does not support tracefs yet?
>> Or do some changes in kernel side on tracefs?
>>
>> And tracefs would be supported in the user mode as well I guess. 
> 
> Hmm...we would need to augment the logic in SELinux to support per-file
> labeling of tracefs via either setxattr or genfs_contexts.  The quick
> fix would be to just add tracefs to the list of whitelisted filesystem
> types in selinux_is_sblabel_mnt(), but the right fix would be to
> generalize this logic as described in the last item on the todo list,
> https://bitbucket.org/seandroid/wiki/wiki/ToDo

Also, you'd need to add an entry to genfs_contexts in the policy to
define a default label for tracefs files.


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