Subject: Re: [PATCH] sctp: Do not trigger BUG_ON when deleting assoc without primary path

From: Daniel Borkmann <[email-masked]>
Date: Thu, 17 Oct 2013 20:01:22 +0200

On 10/17/2013 07:30 PM, Vlad Yasevich wrote:
> It is possible to enter sctp_cmd_delete_tcb() without having a
> primary path.  The situations this most often happens in is
> when duplication cookie processing is triggered.  In this
> case, we are deleting a temporarily created association that
> is not fully populated.   Additially, at the time we
> are deleting the offending association, it is really too
> late to issue a BUG!
>
> This was introduced by:
> commit f9e42b853523cda0732022c2e0473c183f7aec65
> 	net: sctp: sideeffect: throw BUG if primary_path is NULL

Sure, lets remove it, but then we could still get a WARN() [sure,
better than BUG], if the user at the very same time checks procfs
through sctp_seq_dump_local_addrs(), see discussion we had here [1]:

  It may trigger the crash later if the user performs some action on the
  association that touches the primary. That's the reason why I was
  proposing the checks below.

  With the checks in command interpreter, we are only left with the
  possibility that primary_path changes to NULL during the association
  lifetime, which code audit doesn't support right now.  If that ever
  changes we would at least have a bit more information to go on.

  [1] http://patchwork.ozlabs.org/patch/251099/

> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
> index 666c668..1a6eef3 100644
> --- a/net/sctp/sm_sideeffect.c
> +++ b/net/sctp/sm_sideeffect.c
> @@ -860,7 +860,6 @@ static void sctp_cmd_delete_tcb(sctp_cmd_seq_t *cmds,
>   	    (!asoc->temp) && (sk->sk_shutdown != SHUTDOWN_MASK))
>   		return;
>
> -	BUG_ON(asoc->peer.primary_path == NULL);
>   	sctp_unhash_established(asoc);
>   	sctp_association_free(asoc);
>   }
>