net: rds: fix uninitialized trans dereference in CM event handler

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 active side can land on a non-IB device too: the id that
rds_ib_conn_path_connect() creates is not restricted to a node type,
so rdma_resolve_addr() binds it to whichever device serves the local
address, and an iWARP RNIC on the same netdev qualifies.  The crash
there is different: resolving a route on an iWARP id never fills in
cm_id->route.path_rec, and the ROUTE_RESOLVED case writes
path_rec[0].sl before it calls into the transport.

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,
reject a connect request that arrives on a non-IB device, and drop a
connection whose address resolved to one instead of resolving a
route on it.  The rejection is limited to RDMA_CM_EVENT_CONNECT_REQUEST
on purpose: a non-zero return from the handler makes rdma_cm destroy
the id the event was delivered on, which is right for the request's
freshly created id but would free a connection id that RDS still owns
for any other event.  On the active side the id stays ic->i_cm_id and
the connection's shutdown destroys it, so that case returns 0.

Fixes: dcdede0406d3 ("RDS: Drop stale iWARP RDMA transport")
Reported-by: TencentOS Corvus AI <corvus@tencent.com>
Link: https://lore.kernel.org/netdev/20260824111701.2979194-1-ljp1205831794@gmail.com/
Link: https://lore.kernel.org/netdev/20260825021223.3483044-1-ljp1205831794@gmail.com/
Cc: stable@vger.kernel.org
Assisted-by: CodeBuddy:Kimi-K3
Signed-off-by: Aohan Mei <henrymei@tencent.com>
[achender: reject only on RDMA_CM_EVENT_CONNECT_REQUEST instead of
 bailing out for every event on a non-IB device, so that rdma_cm does
 not destroy connection ids RDS still tracks; drop a connection whose
 address resolved to a non-IB device before a route is resolved on it;
 changelog adjusted]
Assisted-by: LLM
Signed-off-by: Allison Henderson <achender@kernel.org>
Link: https://patch.msgid.link/20261003163408.250568-2-achender@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

0 files changed, 0 insertions, 0 deletions