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

[Aohan Mei <ljp1205831794@gmail.com>]

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>
---
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);
-- 
2.43.7