On Fri, 2012-08-10 at 16:36 +0200, Ole Kliemann wrote: > On Fri, Aug 10, 2012 at 09:00:15AM -0400, Stephen Smalley wrote: > > On Fri, 2012-08-10 at 14:11 +0200, Ole Kliemann wrote: > > > I did some runtime test now. I have about 2000 types, 1000 of > > > them (named xIcJ_t, for 0 <= I <= 9, 0 <= J <= 99) each with his > > > own role (xIcJ_r) associated to a user_u. Then there is a user_r > > > and user_t for login. Additionally there is > > > system_u:system_r:root_t with full access to everything. > > > > > > I run the attached script. It creates directories for each of the > > > 1000 types, puts something in it, does a find/grep etc. > > > > > > As system_u:system_r:root_t the script measures an average of > > > about 6sec walltime over 5 runs. (With very little variance.) > > > > > > When I change context to user_u:user_r:user_t even things like > > > 'ls' on home dir or 'id' lag consideribly the first time > > > executed. Just being in this context makes things slow. The > > > script measures an average of about 15sec walltime over 5 runs. > > > > > > That's 2.5 times as much. Who thinks 7% is ridiculously high now? > > > ;-) > > > > > > While it's running the whole system sometimes lags even for just > > > writing on the terminal. top shows spikes of 50%+ CPU on kworker > > > threads. > > > > > > > > > Good side is: It's a clear result and kind of settles the > > > question. If you want a lot of different types for one user, go > > > for categories. > > > > > > > > > But I don't understand this result. Why isn't it slow when root > > > runs the script? He does the same relabeling to all those types. > > > It's not like user_u:user_r:user_t would be running in different > > > type concurrently. Just the fact that user_u is associated with > > > all those types seems to make it slow to run in any context > > > user_u:* > > > > Your result doesn't sound right. Wondering whether you are triggering > > masses of AVC denials (which could then peg syslog or audit) when > > running your script? > > Checked that of course. dmesg showed nothing or just occasional > denials. Just tryed again giving user_t full access to > everything. Changes nothing and dmesg is clear. > > Anyway turns out above I forgot to mention something that > actually is the core of the problem: > > I build a minimal example which is attached. Of course you have > at modify it to your policy. > > Basicly there is one role choke_r with one type choke_t und a > user choke_u with role choke_r. Then are 1000 other types in the > choke role each with a corresponding attribute. > > This alone isn't a problem. But if each of these attributes get > attributed to choke_t, the slowdown starts. Not as bad as > mentioned above but still significantly. (10sec in the test > above.) > > So we have choke_u:choke_r:choke_t. Although all other types are > in choke_r, that alone causes nothing. But as soon as there are > these 1000 attributes on choke_t the fun starts. Actually you > don't even need the 1000 types. Just 1000 attributes on one type > produces a measurable slowdown (7sec) and lags. Having 1000 types > beside just makes it a lot worse. But there absolutely no > slowdown with just 1000 types and no attributes. Interesting. We would expect some slowdown on an AVC cache miss in that situation, although the amount seems troubling. Things to consider: - Does the AVC cache need to be increased or otherwise tuned? You can see some information via the avcstat utility or by directly looking at /sys/fs/selinux/avc. - Does security_compute_av(), which is called on a cache miss, need some profiling and tuning? Particularly the logic within context_struct_compute_av(), where we are iterating through the type attribute ebitmaps. In Fedora 17, most types only have a few attributes (as shown by seinfo -t -x). unconfined_t has a larger number of attributes than most, but even it only has 46 attributes. So we likely don't see this behavior there. -- Stephen Smalley National Security Agency -- This message was distributed to subscribers of the selinux mailing list. If you no longer wish to subscribe, send mail to majordomo@xxxxxxxxxxxxx with the words "unsubscribe selinux" without quotes as the message.
