Re: [PATCH] RDMA/core: Reject CQE counts above max_cqe in ib_cq_pool_get()

[Leon Romanovsky <leon@kernel.org>]

On Mon, Aug 31, 2026 at 08:13:54PM +0300, Serhat Kumral wrote:
> ib_cq_pool_get() does not validate nr_cqe against the device limit,
> while ib_alloc_cqs() caps the size passed to ib_alloc_cq() at
> dev->attrs.max_cqe:
> 
> 	nr_cqes = min(dev->attrs.max_cqe, max(nr_cqes, IB_MAX_SHARED_CQ_SZ));
> 
> If nr_cqe is larger than max_cqe, ib_alloc_cqs() cannot ask the device
> for that many entries. A device that reports the size it was asked for
> therefore returns a CQ smaller than nr_cqe, and the fit test skips
> every CQ in the pool:
> 
> 	if (cq->cqe_used + nr_cqe > cq->cqe)
> 		continue;
> 
> 'found' remains NULL and each iteration calls ib_alloc_cqs() again,
> adding another batch of CQs to dev->cq_pools[]. The CQs stay in the
> pool, so each walk under cq_pools_lock gets longer. The loop ends only
> when an allocation fails, i.e. once the device or the system has run
> out of resources.
> 
> ib_srpt can reach this path when a privileged user configures
> srp_sq_size through configfs. ib_srpt accepts values up to 65535 and
> requests ch->rq_size + sq_size CQEs while establishing a connection. If
> that sum exceeds max_cqe, a valid connection request from a remote
> initiator can trigger the allocation loop.
> 
> Reproduced with ib_srpt over rxe, which reports max_cqe = 32767, after
> setting srp_sq_size to 65535. In a 1 GB guest, a login attempt
> requesting 65663 CQEs caused 115 allocation rounds in 185 ms, followed
> by:
> 
>   Out of memory and no killable processes...
>   Kernel panic - not syncing: System is deadlocked on memory
>   Workqueue: ib_cm cm_work_handler
>   Call Trace:
>    __vmalloc_node_range_noprof
>    vmalloc_user_noprof
>    rxe_queue_init
>    rxe_cq_from_init
>    rxe_create_cq
>    __ib_alloc_cq
>    ib_cq_pool_get
>    srpt_cm_req_recv.cold
>    srpt_rdma_cm_req_recv
>    cma_cm_event_handler
>    cma_ib_req_handler
>    cm_process_work
>    cm_work_handler
> 
> Reject oversized requests before entering the allocation loop. With the
> check in place, the same test allocates no CQs and ib_srpt rejects the
> login:
> 
>   ib_srpt failed to create CQ cqe= 65663 ret= -EINVAL
> 
> Requests for max_cqe entries or fewer behave as before.

Please fix ib_srpt to honor device capabilities.

Thanks

> 
> Fixes: c7ff819aefea ("RDMA/core: Introduce shared CQ pool API")
> Signed-off-by: Serhat Kumral <serhatkumral1@gmail.com>
> ---
>  drivers/infiniband/core/cq.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/infiniband/core/cq.c b/drivers/infiniband/core/cq.c
> index 12304c9a9403..1205e9b28897 100644
> --- a/drivers/infiniband/core/cq.c
> +++ b/drivers/infiniband/core/cq.c
> @@ -449,6 +449,13 @@ struct ib_cq *ib_cq_pool_get(struct ib_device *dev, unsigned int nr_cqe,
>  		return ERR_PTR(-EINVAL);
>  	}
>  
> +	/*
> +	 * ib_alloc_cqs() caps CQ size at max_cqe, so a larger request would
> +	 * keep allocating CQs that never fit until allocation fails.
> +	 */
> +	if (nr_cqe > dev->attrs.max_cqe)
> +		return ERR_PTR(-EINVAL);
> +
>  	num_comp_vectors =
>  		min_t(unsigned int, dev->num_comp_vectors, num_online_cpus());
>  	/* Project the affinty to the device completion vector range */
> 
> base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
> -- 
> 2.53.0
>