Re: [PATCH net] sctp: sctp_epaddr_lookup_transport should be protected by rcu_read_lock

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

On Thu, Dec 15, 2016 at 11:00:55PM +0800, Xin Long wrote:
> Since commit 7fda702f9315 ("sctp: use new rhlist interface on sctp transport
> rhashtable"), sctp has changed to use rhlist_lookup to look up transport, but
> rhlist_lookup doesn't call rcu_read_lock inside, unlike rhashtable_lookup_fast.
> 
> It is called in sctp_epaddr_lookup_transport and sctp_addrs_lookup_transport.
> sctp_addrs_lookup_transport is always in the protection of rcu_read_lock(),
> as __sctp_lookup_association is called in rx path or sctp_lookup_association
> which are in the protection of rcu_read_lock() already.
> 
> But sctp_epaddr_lookup_transport is called by sctp_endpoint_lookup_assoc, it
> doesn't call rcu_read_lock, which may cause "suspicious rcu_dereference_check
> usage' in __rhashtable_lookup.
> 
> This patch is to fix it by adding rcu_read_lock in sctp_endpoint_lookup_assoc
> before calling sctp_epaddr_lookup_transport.
> 
> Fixes: 7fda702f9315 ("sctp: use new rhlist interface on sctp transport rhashtable")
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

> ---
>  net/sctp/endpointola.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sctp/endpointola.c b/net/sctp/endpointola.c
> index 1f03065..410ddc1 100644
> --- a/net/sctp/endpointola.c
> +++ b/net/sctp/endpointola.c
> @@ -331,7 +331,9 @@ struct sctp_association *sctp_endpoint_lookup_assoc(
>  	 * on this endpoint.
>  	 */
>  	if (!ep->base.bind_addr.port)
> -		goto out;
> +		return NULL;
> +
> +	rcu_read_lock();
>  	t = sctp_epaddr_lookup_transport(ep, paddr);
>  	if (!t)
>  		goto out;
> @@ -339,6 +341,7 @@ struct sctp_association *sctp_endpoint_lookup_assoc(
>  	*transport = t;
>  	asoc = t->asoc;
>  out:
> +	rcu_read_unlock();
>  	return asoc;
>  }
>  
> -- 
> 2.1.0
> 
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