Re: [PATCH net v2] net: rds: fix uninitialized trans dereference in CM event handler

[Allison Henderson <achender@kernel.org>]

On Tue, 2026-08-25 at 10:12 +0800, Aohan Mei wrote:
> From: Aohan Mei <henrymei@tencent.com>
> 
> rds_rdma_cm_event_handler_cmn() assigns trans only when the RDMA
> device is an InfiniBand CA (RDMA_NODE_IB_CA).  On any other device
> type, e.g. an iWARP RNIC such as siw, trans stays uninitialized, but
> the event switch dereferences it: unconditionally in the
> RDMA_CM_EVENT_CONNECT_REQUEST case via trans->cm_handle_connect(),
> and (with a connection context) in the ROUTE_RESOLVED and
> ESTABLISHED cases.
> 
> An RDS listener on an iWARP device therefore crashes the kernel as
> soon as a connect request arrives: with CONFIG_INIT_STACK_ALL_ZERO
> the wild load becomes a NULL dereference at offset 0xa0
> (&trans->cm_handle_connect) in the iw_cm_wq workqueue.
> 
> GCC masks the bug in default builds by folding the uninitialized
> load into &rds_ib_transport; Clang-built kernels take the real
> uninitialized path and oops.
> 
> The iWARP transport was dropped long ago and IB is the only
> transport left, so make that explicit: initialize trans to
> &rds_ib_transport at declaration, drop the conditional assignment,
> and reject events from non-IB devices before the event switch.
> 
> Fixes: dcdede0406d3 ("RDS: Drop stale iWARP RDMA transport")
> Reported-by: TencentOS Corvus AI <corvus@tencent.com>
> Cc: stable@vger.kernel.org
> Assisted-by: CodeBuddy:Kimi-K3
> Signed-off-by: Aohan Mei <henrymei@tencent.com>

This looks good to me.  Thanks for the quick response.

Reviewed-by: Allison Henderson <achender@kernel.org>

> ---
> v2:
> - Enforce the IB transport directly instead of NULL-guarding trans,
>   as suggested by Allison Henderson.
> v1: https://lore.kernel.org/netdev/20260824111701.2979194-1-ljp1205831794@gmail.com
>  net/rds/rdma_transport.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/net/rds/rdma_transport.c b/net/rds/rdma_transport.c
> index b15cf316b23a..2c5481f1fcb4 100644
> --- a/net/rds/rdma_transport.c
> +++ b/net/rds/rdma_transport.c
> @@ -52,7 +52,7 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id,
>  {
>  	/* this can be null in the listening path */
>  	struct rds_connection *conn = cm_id->context;
> -	struct rds_transport *trans;
> +	struct rds_transport *trans = &rds_ib_transport;
>  	int ret = 0;
>  	int *err;
>  	u8 len;
> @@ -60,9 +60,6 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id,
>  	rdsdebug("conn %p id %p handling event %u (%s)\n", conn, cm_id,
>  		 event->event, rdma_event_msg(event->event));
>  
> -	if (cm_id->device->node_type == RDMA_NODE_IB_CA)
> -		trans = &rds_ib_transport;
> -
>  	/* Prevent shutdown from tearing down the connection
>  	 * while we're executing. */
>  	if (conn) {
> @@ -80,6 +77,12 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id,
>  		}
>  	}
>  
> +	/* Only the IB transport is supported. */
> +	if (cm_id->device->node_type != RDMA_NODE_IB_CA) {
> +		ret = 1;
> +		goto out;
> +	}
> +
>  	switch (event->event) {
>  	case RDMA_CM_EVENT_CONNECT_REQUEST:
>  		ret = trans->cm_handle_connect(cm_id, event, isv6);