RDMA/rxe: Validate num_sge/cur_sge before indexing wqe->dma.sge[]

Summary

In the Linux kernel, the following vulnerability has been resolved: RDMA/rxe: Validate num_sge/cur_sge before indexing wqe->dma.sge[] For a user QP, qp->sq.queue is a ring the application writes directly, so rxe_post_send() takes the is_user branch and only schedules send_task without validating the WQE. rxe_requester() consumes it in place via req_next_wqe() and calls copy_data(), which indexes &wqe->dma.sge[cur_sge] with the attacker-controlled num_sge/cur_sge. Only the kernel path bounds num_sge (validate_send_wr()); the user WQE is never checked, so a local unprivileged user can post a WQE with an out-of-range cur_sge or oversized num_sge and force an out-of-bounds read of the per-WQE sge array in copy_data() (vmalloc OOB read, local DoS). Bound num_sge to qp->sq.max_sge in rxe_requester() before use, the way get_srq_wqe() already guards SRQ entries, and bound cur_sge only when the WQE carries payload (dma.resid): copy_data() returns early on a zero-length copy before touching dma->sge[], so a zero-payload WQE -- the only kind a max_sge == 0 QP can post -- stays valid. Reproduced under KASAN; the vmalloc-out-of-bounds in copy_data() is gone.