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

[Serhat Kumral <serhatkumral1@gmail.com>]

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.

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