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

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Message-ID: <20130907201203.GB15351@neilslaptop.think-freely.org>
Date:	Sat, 7 Sep 2013 16:12:03 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-sctp@...r.kernel.org, Michio Honda <micchie@....wide.ad.jp>
Subject: Re: [PATCH net] net: sctp: fix smatch warning in
 sctp_send_asconf_del_ip

On Sat, Sep 07, 2013 at 08:51:21PM +0200, 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>
Acked-By: Neil Horman <nhorman@...driver.com>

> ---
>  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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