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

[yanjun.zhu]

On 7/8/26 3:45 PM, Ibrahim Hashimov wrote:
> A user QP's send queue (qp->sq.queue) is a shared ring the userspace
> application writes to directly via mmap (vmalloc_user(), see
> rxe_queue.c). For such a QP, rxe_post_send() takes the qp->is_user
> branch and only schedules the requester task -- it never validates or
> copies the posted WQE:
>
> 	drivers/infiniband/sw/rxe/rxe_verbs.c:
> 		if (qp->is_user) {
> 			rxe_sched_task(&qp->send_task);
> 			...
> 		}
>
> The requester then consumes the WQE in place straight out of that
> mmap'd ring:
>
> 	rxe_req.c:	wqe = req_next_wqe(qp);
> 	rxe_req.c:	err = copy_data(qp->pd, 0, &wqe->dma,
> 					payload_addr(pkt), payload,
> 					RXE_FROM_MR_OBJ);
>
> copy_data() immediately indexes the per-WQE sge array with the
> attacker-controlled cur_sge field, before any bound is checked:
>
> 	rxe_mr.c:	struct rxe_sge *sge = &dma->sge[dma->cur_sge];
> 	rxe_mr.c:	...
> 	rxe_mr.c:	if (sge->length && (offset < sge->length)) {
>
> dma->sge[] is a flex array whose real backing storage is exactly
> qp->sq.max_sge entries per WQE slot (see rxe_qp.c, wqe_size computed
> from max_sge at QP create time). Since a user QP's WQE bytes are
> entirely attacker-supplied, both wqe->dma.num_sge and wqe->dma.cur_sge
> can be set to arbitrary values independent of each other and of
> max_sge. Only the *kernel*-QP post path bounds num_sge:
>
> 	rxe_verbs.c: validate_send_wr()
> 		if (num_sge > sq->max_sge) {
> 			rxe_err_qp(qp, "num_sge > max_sge\n");
>
> but that function is only reachable from rxe_post_one_send() for
> kernel-owned QPs; it is never consulted for a user QP's raw WQE.
>
> The sibling receive path already has the equivalent guard, with the
> literal comment documenting exactly why it is required:
>
> 	rxe_resp.c: get_srq_wqe()
> 		/* don't trust user space data */
> 		if (unlikely(wqe->dma.num_sge > srq->rq.max_sge)) {
> 			...
> 			rxe_dbg_qp(qp, "invalid num_sge in SRQ entry\n");
> 			return RESPST_ERR_MALFORMED_WQE;
> 		}
>
> The send/requester path has no analogous check, so a local,
> unprivileged user who can open /dev/infiniband/uverbs* and create a
> user QP on a soft-RoCE (rxe) link can hand-craft a WQE in the shared
> send queue with an out-of-range wqe->dma.cur_sge (or an oversized
> wqe->dma.num_sge) and ring the send doorbell. rxe_requester() then
> calls copy_data(), which dereferences &dma->sge[cur_sge] out of the
> bounds of the per-WQE sge array -- a vmalloc out-of-bounds *read*
> (confirmed via KASAN: "KASAN: vmalloc-out-of-bounds in copy_data"),
> reliably panicking the kernel (local DoS). sge->addr itself is still
> bounds-checked later by lookup_mr()/rxe_mr_copy(), so the primitive is
> an OOB read of sge metadata, not an arbitrary read/write primitive.
>
> Fix this the same way get_srq_wqe() already does for SRQ entries:
> bound both fields pulled from the (possibly user-mapped) send queue
> entry before they are ever used to index wqe->dma.sge[], right where
> the requester fetches the next WQE off the ring in rxe_requester().
> num_sge is capped at qp->sq.max_sge (matching the sibling SRQ check
> and the kernel-QP validate_send_wr() check), and cur_sge is capped at
> qp->sq.max_sge directly, since that is the true per-WQE array capacity
> that copy_data() indexes into -- this also covers num_sge == 0 /
> cur_sge == 0 local-op and zero-payload WQEs, which remain valid.
>
> This is a long-standing bug in the rxe (soft-RoCE) driver: the
> qp->is_user bypass in rxe_post_send() and the unbounded
> &dma->sge[dma->cur_sge] indexing in copy_data() have been present
> since the driver was introduced.
>
> Runtime-verified on a v6.19 KASAN (CONFIG_KASAN_VMALLOC=y) stand: a
> reproducer that posts a user QP send WQE with an out-of-range
> cur_sge reliably tripped "KASAN: vmalloc-out-of-bounds in
> copy_data" (an out-of-bounds read) before this patch, and no longer
> triggers that report with the patch applied.
>
> Fixes: 8700e3e7c485 ("Soft RoCE driver")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Ibrahim Hashimov <security@xxxxxxxxxxxx>
> Assisted-by: AuditCode-AI:2026.07
> ---
>   drivers/infiniband/sw/rxe/rxe_req.c | 16 ++++++++++++++++
>   1 file changed, 16 insertions(+)
>
> diff --git a/drivers/infiniband/sw/rxe/rxe_req.c b/drivers/infiniband/sw/rxe/rxe_req.c
> index 12d03f390b09..9fb2c49fb503 100644
> --- a/drivers/infiniband/sw/rxe/rxe_req.c
> +++ b/drivers/infiniband/sw/rxe/rxe_req.c
> @@ -701,6 +701,22 @@ int rxe_requester(struct rxe_qp *qp)
>   	if (unlikely(!wqe))
>   		goto exit;
>   
> +	/*
> +	 * Don't trust user space data: qp->sq.queue is a raw ring the
> +	 * application writes directly for a user QP, so wqe->dma.num_sge
> +	 * and wqe->dma.cur_sge must be bounds-checked the same way
> +	 * get_srq_wqe() checks an SRQ entry's num_sge before it is used.
> +	 * Otherwise copy_data() indexes wqe->dma.sge[wqe->dma.cur_sge]
> +	 * with an unvalidated, attacker-controlled index/count and reads
> +	 * out of bounds of the per-wqe sge array.
> +	 */
> +	if (unlikely(wqe->dma.num_sge > qp->sq.max_sge ||

From this function,

static int rxe_init_sq(struct rxe_qp *qp, struct ibv_qp_init_attr 
*init_attr)
{
    ...
    qp->sq.max_sge = init_attr->cap.max_send_sge;
    ...
}

qp->sq.max_sge is also from the user space application. It is possible 
that qp->sq.max_sge is 0.

Then this makes rxe_requester will return error and exit.

Zhu Yanjun

> +		     wqe->dma.cur_sge >= qp->sq.max_sge)) {
> +		rxe_dbg_qp(qp, "invalid num_sge/cur_sge in send wqe\n");
> +		wqe->status = IB_WC_LOC_QP_OP_ERR;
> +		goto err;
> +	}
> +
>   	if (rxe_wqe_is_fenced(qp, wqe)) {
>   		qp->req.wait_fence = 1;
>   		goto exit;