In the Linux kernel, the following vulnerability has been resolved: RDMA/siw: Clear association under lock if siw_qp_modify fails in siw_ac

In the Linux kernel, the following vulnerability has been resolved:

RDMA/siw: Clear association under lock if siw_qp_modify fails in siw_accept

We need to clear cep before release state_lock as siw_qp_llp_close and
siw_qp_modify->siw_qp_llp_close did.

Otherwise if siw_qp_modify() fails in siw_accept(), the QP's state_lock
is released before the error path cleanup. A concurrent ibv_modify_qp()
transitioning the QP to ERROR can race in this window:

siw_accept() ibv_modify_qp(ERROR)

---

siw_qp_modify() fails
up_write(&qp->state_lock)
down_write(&qp->state_lock)
nextstate_from_idle():
if (qp->cep)
siw_cep_put(qp->cep) <- frees cep
qp->cep = NULL
goto error
cep->qp = NULL <- UAF

Clear qp->cep and drop the association reference taken by siw_cep_get(),
all under the write lock held from the initial down_write(&qp->state_lock).
Thread B therefore sees qp->cep == NULL, skips its own put, and cannot free
the cep before siw_accept() is done with it.