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

[Andi Kleen]

> The global list, yes. The task specific list, no. Modifying the local
> list is like any other modification of the cred structure and requires
> the cred be copied.

But you still need to free it eventually right? And that freeing will
need RCU on the reader.

> 
> Moving the lock into smk_access_entry() would introduce a potential
> deadlock in smack_mmap_file. There is a bit of convolution in the
> mmap hook that requires looking at the list in a way that does not
> allow the locking to be embedded where it used to be.

rcu_read_lock() is just a per task counter and nests fine and never deadlocks.

-Andi
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