netdev - Re: [PATCH net] net: sctp: fix smatch warning in sctp_send_asconf_del

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Message-ID: <20130907201128.GA15351@neilslaptop.think-freely.org>
Date:	Sat, 7 Sep 2013 16:11:28 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Michio Honda <micchie@....wide.ad.jp>
Cc:	Daniel Borkmann <dborkman@...hat.com>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-sctp@...r.kernel.org
Subject: Re: [PATCH net] net: sctp: fix smatch warning in
 sctp_send_asconf_del_ip

On Sat, Sep 07, 2013 at 09:40:15PM +0200, Michio Honda wrote:
> Hi, 
> 
> Sorry for that I didn't respond to that warning.
> You are right, laddr == NULL && addrcnt == 1 is the indicator of the function called by
> asconf_mgmt().
> 
> Since your patch is actually redundant, I would suggest putting comment on the 
> line of "if ((laddr == NULL) && (addrcnt == 1)) {", and/or on the checking in your patch.
> 
How can you guarantee its redundant, it seems possible to me to have an
association for which the laddr might not be found (the NULL case) while having
a multientry bind list, leading to a NULL dereference?  I think we need the
check.

Or do you mean to indicate that checkout laddr == NULL & addrcnt == 1 is
actually redundant.  If so, where is the redundant check?
Neil

> Cheers,
> - Michio
>  
> On Sep 7, 2013, at 8:51 PM, Daniel Borkmann wrote:
> 
> > This was originally reported in [1] and posted by Neil Horman [2], he said:
> > 
> >  Fix up a missed null pointer check in the asconf code. If we don't find
> >  a local address, but we pass in an address length of more than 1, we may
> >  dereference a NULL laddr pointer. Currently this can't happen, as the only
> >  users of the function pass in the value 1 as the addrcnt parameter, but
> >  its not hot path, and it doesn't hurt to check for NULL should that ever
> >  be the case.
> > 
> > The callpath from sctp_asconf_mgmt() looks okay. But this could be triggered
> > from sctp_setsockopt_bindx() call with SCTP_BINDX_REM_ADDR and addrcnt > 1
> > while passing all possible addresses from the bind list to SCTP_BINDX_REM_ADDR
> > so that we do *not* find a single address in the association's bind address
> > list that is not in the packed array of addresses. If this happens when we
> > have an established association with ASCONF-capable peers, then we could get
> > a NULL pointer dereference as we only check for laddr == NULL && addrcnt == 1
> > and call later sctp_make_asconf_update_ip() with NULL laddr.
> > 
> > BUT: this actually won't happen as sctp_bindx_rem() will catch such a case
> > and return with an error earlier. As this is incredably unintuitive and error
> > prone, add a check to catch at least future bugs here. As Neil says, its not
> > hot path. Introduced by 8a07eb0a5 ("sctp: Add ASCONF operation on the
> > single-homed host").
> > 
> > [1] http://www.spinics.net/lists/linux-sctp/msg02132.html
> > [2] http://www.spinics.net/lists/linux-sctp/msg02133.html
> > 
> > Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> > Signed-off-by: Neil Horman <nhorman@...driver.com>
> > Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
> > Cc: Michio Honda <micchie@....wide.ad.jp>
> > ---
> > net/sctp/socket.c | 3 +++
> > 1 file changed, 3 insertions(+)
> > 
> > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > index 5462bbb..911b71b 100644
> > --- a/net/sctp/socket.c
> > +++ b/net/sctp/socket.c
> > @@ -806,6 +806,9 @@ static int sctp_send_asconf_del_ip(struct sock		*sk,
> > 			goto skip_mkasconf;
> > 		}
> > 
> > +		if (laddr == NULL)
> > +			return -EINVAL;
> > +
> > 		/* We do not need RCU protection throughout this loop
> > 		 * because this is done under a socket lock from the
> > 		 * setsockopt call.
> > -- 
> > 1.7.11.7
> > 
> 
> 
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