Re: [PATCH] SMACK: Add missing rcu_read_lock/unlock for processcapability walk.

[Andi Kleen]

On Wed, Apr 20, 2011 at 03:51:41PM -0700, Casey Schaufler wrote:
> On 4/20/2011 3:00 PM, Andi Kleen wrote:
> > From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> >
> > smk_access_entry does a RCU list walk for a list shared with other
> > threads. It relies on the caller doing rcu_read_lock().
> > One caller forgot to do to this, which could lead to races
> > on preemptible kernels.
> >
> > Move the rcu_read_lock() into smk_access_entry instead.
> 
> Nacked-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> 
> The lock was moved out of smk_access_entry in support of the
> processing done in the smack_mmap_file() hook. Where do you see
> a potential race, and which caller "forgot" to do the lock?

There are two callers and only one takes it.
The one that doesn't take it is smk_curacc.

I checked the callers of that and there is no rcu_read_lock() in those

As far as I understand the cred which holds this list is shared
between threads and other threads can modify it. Which means 
it needs RCU read lock protection.

-Andi
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