Re: [PATCH 2.6.29.6 - 2.6.35-rc3] CRED: Release spinlock before commit_creds().

[David Howells <dhowells@redhat.com>]

Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> wrote:

> reparent_to_kthreadd() is calling commit_creds() with tasklist_lock held.
> But commit_creds() calls
> key_fsuid_changed()/key_fsgid_changed()/proc_id_connector() which may sleep.
> Release tasklist_lock before calling commit_creds().

Hmmm...  Does this change leave a hole in which the thread can be accessed as
it's not locked away, but still has the old credentials?

I wonder if we should have an internal CLONE_KTHREAD flag to achieve this in
do_fork() rather than daemonize()'ing the thread later.

Also, key_fsuid_changed() and key_fsgid_changed() should be skipped in
commit_creds() if the thread-keyring pointer in the new creds is not the same
as that in the old creds (as will be the case if we're shifting to init_cred),
so they shouldn't really be a problem.

However, I can't see an easy way around proc_id_connector() sleeping - unless
we just don't call it if new == &init_cred in commit_creds().

I suppose it also leaves a hole if we call commit_creds() first, before
getting the write_lock()... :-/

David