[PATCH V3 1/2] security: Add a cred_getsecid hook

[Stephen Smalley]

On Mon, 2017-10-30 at 10:57 +0000, Matthew Garrett via Selinux wrote:
> On Thu, Oct 26, 2017 at 3:20 PM, Stephen Smalley <sds at tycho.nsa.gov>
> wrote:
> > On Thu, 2017-10-26 at 01:40 -0700, Matthew Garrett via Selinux
> > wrote:
> > > +static void selinux_cred_getsecid(const struct cred *c, u32
> > > *secid)
> > > +{
> > > +     rcu_read_lock();
> > > +     *secid = cred_sid(c);
> > > +     rcu_read_unlock();
> > 
> > Is rcu_read_lock() necessary here? Seems like we use cred_sid() in
> > many
> > places without it.
> 
> Ah, I thought it was based on task_sid(), but I guess that's actually
> protecting the __task_cred()?

It appears to me that in all other cases, we are either dealing with
the current cred, or something in the call chain of cred_sid() is
holding a reference to the cred, or something in the call chain of
cred_sid() has called rcu_read_lock() already.  I might have missed
something though, and I don't know how safe it is to assume that all
future callers will do this.  cc'd David for his thoughts.

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