[Devel] Re: [PATCH RFC] User namespaces: general cleanups

[Serge E. Hallyn]

Quoting David Howells (dhowells at redhat.com):
> Serge E. Hallyn <serue at us.ibm.com> wrote:
> 
> > Hmm, with this patch, with CONFIG_KEYS=y users in child user_namespaces
> > never get freed.  Ones in the init_user_ns do, and with CONFIG_KEYS=n,
> > those in child user_namespaces do as well.
> > 
> > I don't see anything obvious in copy_creds() that would cause this...
> 
> Try looking in lookup_user_key().  Also, can you try the attached patch?

That patch seems to fix it!  Also seemed fine under ltp.

> I've also attached a better version of your debugging patch, one that
> differentiates between allocated and reused user_structs.
> 
> David
> ---
> From: David Howells <dhowells at redhat.com>
> 
> CRED: Fix creds refcounting in lookup_user_key()
> 
> Make lookup_user_key() drop at all return points the reference to the current
> creds that it took at the top of the function
> 
> Signed-off-by: David Howells <dhowells at redhat.com>

Tested-by: Serge Hallyn <serue at us.ibm.com>

> ---
> 
>  security/keys/process_keys.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> 
> diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
> index e40f61d..2d6076d 100644
> --- a/security/keys/process_keys.c
> +++ b/security/keys/process_keys.c
> @@ -667,6 +667,7 @@ try_again:
>  		goto invalid_key;
> 
>  error:
> +	put_cred(cred);
>  	return key_ref;
> 
>  invalid_key:
> 
> ---
> >From e00a2d98dd1086b0c863d8b416df33280c7c2574 Mon Sep 17 00:00:00 2001
> From: Serge Hallyn <serue at us.ibm.com>
> Date: Mon, 13 Oct 2008 16:36:05 -0500
> Subject: [PATCH 1/1] creds: print user_struct refcounts
> 
> print user_struct refcounts at alloc, and print msg at uid free.

Yup, except you've tossed the user namespace refcounting checks :)
(But that's ok, we all know user namespaces are bug-free.)

Anyway, will you push the refcounting fix to James?  Then I'll
resend the user namespaces patch merged with your patch (if you
don't mind) plus the clearing of groups and keyrings for a new
user-namespace tomorrow.

thanks,
-serge

> Signed-off-by: Serge Hallyn <serue at us.ibm.com>
> Signed-off-by: David Howells <dhowells at redhat.com>
> ---
> 
>  kernel/user.c |   12 +++++++++++-
>  1 files changed, 11 insertions(+), 1 deletions(-)
> 
> 
> diff --git a/kernel/user.c b/kernel/user.c
> index d476307..073296e 100644
> --- a/kernel/user.c
> +++ b/kernel/user.c
> @@ -317,6 +317,7 @@ done:
>  static inline void free_user(struct user_struct *up, unsigned long flags)
>  {
>  	/* restore back the count */
> +	printk(KERN_NOTICE "%s: freeing a uid (%d)\n", __func__, up->uid);
>  	atomic_inc(&up->__count);
>  	spin_unlock_irqrestore(&uidhash_lock, flags);
> 
> @@ -337,6 +338,7 @@ static inline void uids_mutex_unlock(void) { }
>   */
>  static inline void free_user(struct user_struct *up, unsigned long flags)
>  {
> +	printk(KERN_NOTICE "%s: freeing a uid (%d)\n", __func__, up->uid);
>  	uid_hash_remove(up);
>  	spin_unlock_irqrestore(&uidhash_lock, flags);
>  	sched_destroy_user(up);
> @@ -422,16 +424,24 @@ struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid)
>  			key_put(new->uid_keyring);
>  			key_put(new->session_keyring);
>  			kmem_cache_free(uid_cachep, new);
> +			printk(KERN_NOTICE "%s: reuse a uid (%d) (cnt %u)\n",
> +			       __func__, uid, atomic_read(&up->__count));
> +
>  		} else {
>  			uid_hash_insert(new, hashent);
>  			up = new;
> +			printk(KERN_NOTICE "%s: alloced a uid (%d) (cnt %u)\n",
> +			       __func__, uid, atomic_read(&up->__count));
> +
>  		}
>  		spin_unlock_irq(&uidhash_lock);
> 
> +	} else {
> +		printk(KERN_NOTICE "%s: reuse a uid (%d) (cnt %u)\n",
> +		       __func__, uid, atomic_read(&up->__count));
>  	}
> 
>  	uids_mutex_unlock();
> -
>  	return up;
> 
>  out_destoy_sched:
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