Re: [PATCH v2] RDMA/rxe: fix responder UAF on IB_QP_MAX_DEST_RD_ATOMIC modify_qp

["yanjun.zhu" <yanjun.zhu@linux.dev>]

On 7/9/26 12:26 AM, Ibrahim Hashimov wrote:
> rxe_qp_from_attr()'s IB_QP_MAX_DEST_RD_ATOMIC branch frees and
> reallocates qp->resp.resources[] (the rd_atomic resource array used by
> the responder to track in-flight RDMA READ/ATOMIC/FLUSH requests)
> completely outside of the IB_QP_STATE handling above it. Unlike every
> other place that tears this array down -- rxe_qp_reset(), reached only
> under IB_QP_STATE, always calls rxe_disable_task(&qp->recv_task) /
> rxe_disable_task(&qp->send_task) to drain the responder and requester
> tasks before touching per-QP state, then re-enables them -- this branch
> runs with the responder task (rxe_receiver(), scheduled as recv_task on
> the rxe_wq workqueue) fully live and unlocked. A userspace modify_qp()
> that sets only IB_QP_MAX_DEST_RD_ATOMIC (no state change, so
> __qp_chk_state()/ib_modify_qp_is_ok() never runs and qp->state_lock is
> never taken here) can therefore race the responder in two ways:
> 
>   1. free_rd_atomic_resources() calls kfree(qp->resp.resources) and
>      alloc_rd_atomic_resources() kzalloc_objs()'s a new array while
>      rxe_prepare_res()/find_resource() in rxe_resp.c are concurrently
>      walking &qp->resp.resources[i] with no lock held -- a straight
>      free-vs-read race on the array itself.
> 
>   2. free_rd_atomic_resources() only NULLs qp->resp.resources; it never
>      clears qp->resp.res, the raw pointer *into* that array that
>      rxe_resp.c caches across a multi-packet RDMA READ/ATOMIC/FLUSH
>      reply (set at rxe_resp.c read/atomic/flush-reply sites, cleared
>      only on the normal completion paths). If a modify_qp() races a
>      resource still referenced by qp->resp.res, the array is freed out
>      from under the cached pointer and the next reply packet dereferences
>      it -- independent of the kfree/kzalloc_objs() window in (1).
> 
> Reproduced with KASAN: a single process driving one RC QP pair in rxe
> loopback, one thread pumping large multi-packet IBV_WR_RDMA_READs
> against qpB while a second thread hammers
> ibv_modify_qp(qpB, IB_QP_MAX_DEST_RD_ATOMIC), reliably (~11s) produces
> 
>    BUG: KASAN: slab-use-after-free in rxe_receiver+0x4f78/0x89e0 [rdma_rxe]
>    Workqueue: rxe_wq do_work [rdma_rxe]
> 
> with the freed kmalloc-1k object being the rd_atomic resource array
> freed by the modify_qp() thread while the recv_task kworker reads it.
> An identical run modifying only IB_QP_MIN_RNR_TIMER (no resource free)
> is clean.
> 
> Fix both races the same way rxe_qp_reset() already handles tearing down
> this exact array: quiesce the responder task around the free/realloc by
> calling rxe_disable_task(&qp->recv_task) before free_rd_atomic_resources()
> and rxe_enable_task(&qp->recv_task) only after alloc_rd_atomic_resources()
> has succeeded, so rxe_receiver() cannot observe the array mid-free/
> mid-realloc. On the alloc-failure path the responder is deliberately
> left quiesced: qp->resp.resources is NULL at that point and
> rxe_prepare_res()/find_resource() would dereference it, so recv_task
> must not be re-enabled until a fresh array has been installed. And
> close the still-open window for (2) at the source: have
> free_rd_atomic_resources() clear qp->resp.res along with
> qp->resp.resources, exactly like the existing completion paths in
> rxe_resp.c (check_rkey()/duplicate_request()/RESPST_CLEANUP) already do
> when a resource's lifetime ends, so a drained-and-resumed responder
> restarts at RESPST_CHK_PSN against the fresh array instead of replaying
> a stale reference into the old one.
> 
> Only qp->recv_task is drained: qp->resp.resources / qp->resp.res are
> touched exclusively by the responder (rxe_resp.c); the requester
> (send_task / rxe_sender()) never reads them, so there is no need to
> widen this beyond what rxe_qp_reset() would drain for the equivalent
> state.
> 
> Verified on the same v6.19 KASAN stand: with this fix applied, the
> identical differential reproducer drives sustained MAX_DEST_RD_ATOMIC
> storms against qpB well past the ~11s pre-fix time-to-first-splat with
> zero KASAN reports, versus reliably tripping the slab-use-after-free in
> rxe_receiver() described above before the fix.
> 
> Fixes: 8700e3e7c485 ("Soft RoCE driver")
> Cc: stable@vger.kernel.org
> Signed-off-by: Ibrahim Hashimov <security@auditcode.ai>
> Assisted-by: AuditCode-AI:2026.07
> ---
> v2: address Zhu Yanjun's review of v1
>      (https://lore.kernel.org/linux-rdma/20260708224550.1281-1-security@auditcode.ai/):
>      only re-enable recv_task after alloc_rd_atomic_resources() succeeds, so
>      the responder is not resumed against a NULL qp->resp.resources on the
>      ENOMEM path (rxe_prepare_res()/find_resource() would dereference it).
>      No change to the successful path; fix description updated accordingly.
> 
>   drivers/infiniband/sw/rxe/rxe_qp.c | 16 +++++++++++++++-
>   1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/sw/rxe/rxe_qp.c b/drivers/infiniband/sw/rxe/rxe_qp.c
> index f3dff1aea96a..e39fb144cbbb 100644
> --- a/drivers/infiniband/sw/rxe/rxe_qp.c
> +++ b/drivers/infiniband/sw/rxe/rxe_qp.c
> @@ -172,6 +172,7 @@ static void free_rd_atomic_resources(struct rxe_qp *qp)
>   		}
>   		kfree(qp->resp.resources);
>   		qp->resp.resources = NULL;
> +		qp->resp.res = NULL;
>   	}
>   }
>   
> @@ -709,11 +710,24 @@ int rxe_qp_from_attr(struct rxe_qp *qp, struct ib_qp_attr *attr, int mask,
>   
>   		qp->attr.max_dest_rd_atomic = max_dest_rd_atomic;
>   
> +		/*
> +		 * This branch is not gated by IB_QP_STATE, so the responder
> +		 * task is live here. Quiesce it the way rxe_qp_reset() does
> +		 * before swapping the rd_atomic resource array, so
> +		 * rxe_receiver() cannot race the free/realloc.
> +		 */
> +		rxe_disable_task(&qp->recv_task);
>   		free_rd_atomic_resources(qp);
> -
>   		err = alloc_rd_atomic_resources(qp, max_dest_rd_atomic);
> +		/*
> +		 * On failure the responder stays quiesced: qp->resp.resources
> +		 * is NULL now, and rxe_prepare_res()/find_resource() would
> +		 * dereference it, so do not re-enable recv_task until a fresh
> +		 * array has been installed.
> +		 */
>   		if (err)
>   			return err;
> +		rxe_enable_task(&qp->recv_task);

Thanks a lot. I am fine with this commit. Please Leon and Jason comment 
on this commit.

Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>

Zhu Yanjun

>   	}
>   
>   	if (mask & IB_QP_EN_SQD_ASYNC_NOTIFY)