Hi Bill,

Agreed with you about the combination of write and executable is bad. However, 
given that the app is already installed on the device, if it is malicious, the 
damage is already done. So I’m not sure preventing that malicious app to inject 
more code has great value.

Also, I noticed that when I started some app initially it starts downloading 
more code before fully functioning.  I wonder if the developers do it to 
minimize the size of the app in play store as well as to simplifying the 
upgrade process (i.e., doesn’t need to upgrade the version in play store).


From: William Roberts 
<[email protected]<mailto:[email protected]>>
Date: Thursday, February 13, 2014 at 10:42 PM
To: Tai Nguyen <[email protected]<mailto:[email protected]>>
Cc: "[email protected]<mailto:[email protected]>" 
<[email protected]<mailto:[email protected]>>
Subject: Re: Missing executable permission for app domain to use its shared 
library?


In general you should avoid write and execute together. Its an entry point for 
code injection. However, apps that  DL their own so files for dynamic loading 
will trigger this.

The proper way of app updating is Google play. The proper way of running 
libraries is to pkg them with the apk. Apps however don't do this. I'm curious 
if this rule is on aosp master..and if not is this bad practice going to be 
stopped.

On Feb 13, 2014 6:27 PM, "Tai Nguyen (tainguye)" 
<[email protected]<mailto:[email protected]>> wrote:
I got this audit message when running the Xray app

audit(1390917101.250:6): avc:  denied  { execute } for  pid=5371 
comm=4173796E635461736B202331 
path="/data/data/com.duosecurity.xray/files/libashmem_v1.so" dev=dm-0 
ino=155658 scontext=u:r:untrusted_app:s0 tcontext=u:object_r:app_data_file:s0 
tclass=file

It seems like it just uses its code, so it should be allowed to do that. 
However, I look at the app.te and we only give app_domain create_file_perms 
which doesn’t include executable permission.


# App sandbox file accesses.

allow appdomain app_data_file:dir create_dir_perms;

allow appdomain app_data_file:notdevfile_class_set create_file_perms;

So, why don’t we give app domain executable permission for its data file?

Thanks,
Tai



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