Re: Give out all the avc logs in ome time

[Stephen Smalley <sds@tycho.nsa.gov>]

On 05/04/2015 10:06 PM, Zhi Xin wrote:
> Hi All,
> 
>  
> 
> In my daily work, I’m always solving the selinux deny as presented by
> avc log. But I found that, for one particular test, selinux cannot give
> me all the avc deny log in one time, which has slowed down a lot of my
> daily work.
> 
>  
> 
> For example, I trigger a process called test_daemon to access a
> /dev/test_device in a particular test. Totally, it should have “open,
> read, write, ioctl” for permissions. But for one time test, I only catch
> “open, read” related avc log. And only after I have merged a patch to
> give the “open” and “read” permission, I rerun the test. The “write
> ioctl” related avc  logs start to occur. So my question is how can I get
> “open, read, write, ioctl” avc log in one test.
> 
>  
> 
> I have done a little study on this issue. selinux avc log depends on
> audit subsystem. In /kernel/kernel/audit.c, some code has indicated that
> we may lost the records in five ways:
> 
> 115 <http://10.38.120.31:8080/source/xref/pxa1928-lp5.0/kernel/kernel/audit.c#115>/* Records can be lost in several ways:
> 
> 116 <http://10.38.120.31:8080/source/xref/pxa1928-lp5.0/kernel/kernel/audit.c#116>   0) [suppressed in audit_alloc]
> 
> 117 <http://10.38.120.31:8080/source/xref/pxa1928-lp5.0/kernel/kernel/audit.c#117>   1) out of memory in audit_log_start [kmalloc of struct audit_buffer]
> 
> 118 <http://10.38.120.31:8080/source/xref/pxa1928-lp5.0/kernel/kernel/audit.c#118>   2) out of memory in audit_log_move [alloc_skb]
> 
> 119 <http://10.38.120.31:8080/source/xref/pxa1928-lp5.0/kernel/kernel/audit.c#119>   3) suppressed due to audit_rate_limit
> 
> 120 <http://10.38.120.31:8080/source/xref/pxa1928-lp5.0/kernel/kernel/audit.c#120>   4) suppressed due to audit_backlog_limit
> 
> 121 <http://10.38.120.31:8080/source/xref/pxa1928-lp5.0/kernel/kernel/audit.c#121>*/
> 
>  
> 
> So is this the root-cause of my issue ? How can I modify kernel code to
> archieve my purpose or there already is a open/off switch to help me on
> giving all the logs in one time test ?

(cc'ing seandroid-list as you later mentioned that you are encountering
this in the context of Android, although I don't know if it is truly
specific to Android)

Generally you should see audit_lost= log messages in dmesg if audit log
messages were lost, although those are also subject to the printk
ratelimit and could be suppressed.

One thing you can try is to disable the audit ratelimit, which in
Android is set by system/core/logd/libaudit.c.  Just remove the
AUDIT_STATUS_RATE_LIMIT flag from status.mask and don't bother setting
status.rate_limit.

We also carry a patch in our kernel branches for Nexus devices that
disables the printk ratelimit for audit messages. e.g.
https://bitbucket.org/seandroid/kernel-msm/commits/0388e1630648c481e42929135babb1dbba272e27