Re: [PATCH] CRED: Fix regression in cap_capable() as shown up by sys_faccessat() [ver #2]
From: David Howells
Date: Mon Jan 05 2009 - 16:12:56 EST
Serge E. Hallyn <serue@xxxxxxxxxx> wrote:
> You have the 'acting_as' name for subj/eff, which I like. Is there
> another name you could use in place of 'real' in the name
> task_real_capable()?
Ummm... 'Actual' or 'Assigned' perhaps?
> I do find this version much easier to read. It seems easier to
> track capable+current_cred() vs real_capable+get_task_cred(). Could
> you do a few benchmarks to gauge whether the difference the
> optimization makes?
Yeah... My main objection is passing around two or three superfluous arguments
in the common case. Most of the time, the only necessary argument to
sec->capable():
int (*capable) (struct task_struct *tsk, const struct cred *cred,
int cap, int audit);
is cap; tsk, cred and audit are all superfluous in the (very) common case.
How about:
int (*fast_capable) (int cap);
which assumes current, current_cred() and SECURITY_CAP_AUDIT?
Benchmarking is tricky, given that the individual savings will be relatively
small in comparison to the code that calls them.
However, if I can get rid of three arguments passed into each of
security_capable(), selinux_capable() and cap_capable(), that really should
speed things up if you call it enough times, especially as current is held in a
register on some archs.
I'll see what I can do.
> I'm looking at a several-week-old linux-next, but only see one use of
> capable on another task which audits, and that is in commoncap for
> traceme, so it seems reasonable.
Should has_capability() be out of lines and have security_real_capable() merged
into it? And the same for has_capability_noaudit() and
security_real_capable_noaudit()?
> So yeah, I do like this version better.
Perhaps a separate patch to optimise capable(). As I said, I'll see about
benchmarking it.
David
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