Re: [PATCH net] net: sctp: fix smatch warning in sctp_send_asconf_del_ip

[Vlad Yasevich <vyasevich@gmail.com>]

On 09/07/2013 02:51 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@oracle.com>
> Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
> Cc: Michio Honda <micchie@sfc.wide.ad.jp>

Acked-by: Vlad Yasevich <vyasevich@gmail.com>

-vlad

> ---
>   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.
>