Subject: Re: [PATCH] rds: avoid potential stack overflow

From: Sowmini Varadhan <[email-masked]>
Date: Mon, 09 Mar 2015 10:19:41 -0400

On 03/09/2015 08:06 AM, Arnd Bergmann wrote:
> The rds_iw_add_conn function stores a large 'struct rds_sock'

I think you might have a typo here- did you mean
rds_iw_update_cm_id above (which is the function that has
a 'struct rds_sock rs' on the stack)?

The rest of the change looks fine to me.

--Sowmini

> object on the stack in order to pass a pair of addresses. This
> happens to just fit withint the 1024 byte stack size warning
> limit on x86, but just exceed that limit on ARM, which gives
> us this warning:
>
> net/rds/iw_rdma.c:200:1: warning: the frame size of 1056 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>
> The warning is correct in principle, though unlikely to be
> related to a serious problem.
>
> As the use of this large variable is basically bogus, we can
> rearrange the code to not do that. Instead of passing an
> rds socket into rds_iw_get_device, we now just pass the two
> addresses that we have available in rds_iw_update_cm_id, and
> we change rds_iw_get_mr accordingly, to create two address
> structures on the stack there.
>
> Signed-off-by: Arnd Bergmann <[email-masked]>
>
> diff --git a/net/rds/iw_rdma.c b/net/rds/iw_rdma.c
> index a817705ce2d0..dba8d0864f18 100644
> --- a/net/rds/iw_rdma.c
> +++ b/net/rds/iw_rdma.c
> @@ -88,7 +88,9 @@ static unsigned int rds_iw_unmap_fastreg_list(struct rds_iw_mr_pool *pool,
>   			int *unpinned);
>   static void rds_iw_destroy_fastreg(struct rds_iw_mr_pool *pool, struct rds_iw_mr *ibmr);
>
> -static int rds_iw_get_device(struct rds_sock *rs, struct rds_iw_device **rds_iwdev, struct rdma_cm_id **cm_id)
> +static int rds_iw_get_device(struct sockaddr_in *src, struct sockaddr_in *dst,
> +			     struct rds_iw_device **rds_iwdev,
> +			     struct rdma_cm_id **cm_id)
>   {
>   	struct rds_iw_device *iwdev;
>   	struct rds_iw_cm_id *i_cm_id;
> @@ -112,15 +114,15 @@ static int rds_iw_get_device(struct rds_sock *rs, struct rds_iw_device **rds_iwd
>   				src_addr->sin_port,
>   				dst_addr->sin_addr.s_addr,
>   				dst_addr->sin_port,
> -				rs->rs_bound_addr,
> -				rs->rs_bound_port,
> -				rs->rs_conn_addr,
> -				rs->rs_conn_port);
> +				src->sin_addr.s_addr,
> +				src->sin_port,
> +				dst->sin_addr.s_addr,
> +				dst->sin_port);
>   #ifdef WORKING_TUPLE_DETECTION
> -			if (src_addr->sin_addr.s_addr == rs->rs_bound_addr &&
> -			    src_addr->sin_port == rs->rs_bound_port &&
> -			    dst_addr->sin_addr.s_addr == rs->rs_conn_addr &&
> -			    dst_addr->sin_port == rs->rs_conn_port) {
> +			if (src_addr->sin_addr.s_addr == src->sin_addr.s_addr &&
> +			    src_addr->sin_port == src->sin_port &&
> +			    dst_addr->sin_addr.s_addr == dst->sin_addr.s_addr &&
> +			    dst_addr->sin_port == dst->sin_port) {
>   #else
>   			/* FIXME - needs to compare the local and remote
>   			 * ipaddr/port tuple, but the ipaddr is the only
> @@ -128,7 +130,7 @@ static int rds_iw_get_device(struct rds_sock *rs, struct rds_iw_device **rds_iwd
>   			 * zero'ed.  It doesn't appear to be properly populated
>   			 * during connection setup...
>   			 */
> -			if (src_addr->sin_addr.s_addr == rs->rs_bound_addr) {
> +			if (src_addr->sin_addr.s_addr == src->sin_addr.s_addr) {
>   #endif
>   				spin_unlock_irq(&iwdev->spinlock);
>   				*rds_iwdev = iwdev;
> @@ -180,19 +182,13 @@ int rds_iw_update_cm_id(struct rds_iw_device *rds_iwdev, struct rdma_cm_id *cm_i
>   {
>   	struct sockaddr_in *src_addr, *dst_addr;
>   	struct rds_iw_device *rds_iwdev_old;
> -	struct rds_sock rs;
>   	struct rdma_cm_id *pcm_id;
>   	int rc;
>
>   	src_addr = (struct sockaddr_in *)&cm_id->route.addr.src_addr;
>   	dst_addr = (struct sockaddr_in *)&cm_id->route.addr.dst_addr;
>
> -	rs.rs_bound_addr = src_addr->sin_addr.s_addr;
> -	rs.rs_bound_port = src_addr->sin_port;
> -	rs.rs_conn_addr = dst_addr->sin_addr.s_addr;
> -	rs.rs_conn_port = dst_addr->sin_port;
> -
> -	rc = rds_iw_get_device(&rs, &rds_iwdev_old, &pcm_id);
> +	rc = rds_iw_get_device(src_addr, dst_addr, &rds_iwdev_old, &pcm_id);
>   	if (rc)
>   		rds_iw_remove_cm_id(rds_iwdev, cm_id);
>
> @@ -598,9 +594,17 @@ void *rds_iw_get_mr(struct scatterlist *sg, unsigned long nents,
>   	struct rds_iw_device *rds_iwdev;
>   	struct rds_iw_mr *ibmr = NULL;
>   	struct rdma_cm_id *cm_id;
> +	struct sockaddr_in src = {
> +		.sin_addr.s_addr = rs->rs_bound_addr,
> +		.sin_port = rs->rs_bound_port,
> +	};
> +	struct sockaddr_in dst = {
> +		.sin_addr.s_addr = rs->rs_conn_addr,
> +		.sin_port = rs->rs_conn_port,
> +	};
>   	int ret;
>
> -	ret = rds_iw_get_device(rs, &rds_iwdev, &cm_id);
> +	ret = rds_iw_get_device(&src, &dst, &rds_iwdev, &cm_id);
>   	if (ret || !cm_id) {
>   		ret = -ENODEV;
>   		goto out;
>
> --
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