Re: [PATCH v2] RDMA/uverbs: Make CQ handle mandatory for WQ creation

[Kalesh Anakkur Purayil]

On Fri, Sep 11, 2026 at 7:46 AM lirongqing <lirongqing@xxxxxxxxx> wrote:

From: Li RongQing <lirongqing@xxxxxxxxx>

UVERBS_ATTR_CREATE_WQ_CQ_HANDLE is declared UA_OPTIONAL in the ioctl
method definition, so the mandatory attribute bitmap does not enforce
its presence.  When userspace omits it, uverbs_attr_get_obj() returns
ERR_PTR(-ENOENT) and the handler stores that error pointer into
wq_init_attr.cq without validation.

The bogus cq pointer is then passed to the driver's create_wq callback.
In the mlx5 case, create_rq() calls to_mcq(init_attr->cq) which applies
container_of to the ERR_PTR value, producing a near-NULL pointer.  The
subsequent access in get_rq_ts_format() triggers a kernel NULL pointer
dereference:

  BUG: kernel NULL pointer dereference, address: 0000000000000296
  RIP: 0010:create_rq+0x32/0x550 [mlx5_ib]
  Call Trace:
   mlx5_ib_create_wq+0x14a/0x210 [mlx5_ib]
   ib_uverbs_handler_UVERBS_METHOD_WQ_CREATE+0x1f0/0x320 [ib_uverbs]
   ib_uverbs_run_method+0x296/0x320 [ib_uverbs]
   ib_uverbs_cmd_verbs+0x1a0/0x260 [ib_uverbs]
   ib_uverbs_ioctl+0xa8/0x120 [ib_uverbs]

A WQ without a CQ was never valid; the legacy write path always required
one via uobj_get_obj_read() in ib_uverbs_ex_create_wq().  Declare the
attribute UA_MANDATORY so the uverbs framework rejects the ioctl early
when the CQ handle is missing, before the handler ever runs.

Fixes: ef3bc084a8ed ("IB/uverbs: Introduce create/destroy WQ commands over ioctl")
Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>

 

LGTM, 

Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@xxxxxxxxxxxx> 

--

Regards,

Kalesh AP

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