Re: [PATCH] fix: infiniband/rxe: check_rkey: fix refcount underflow due to unchecked rxe_get return value

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

On 6/26/26 8:05 AM, WenTao Liang wrote:
> rxe_get is a conditional get (kref_get_unless_zero) that returns 0 when
>    the object's refcount is already zero. In check_rkey, the return value of
>    rxe_get(mr) is ignored. If rxe_get fails (returns 0), the code continues
>    to use mr without a valid reference, and error paths will call
>    rxe_put(mr) on an unheld reference, causing a refcount underflow.
> 
> Check the return value of rxe_get and bail out with an error when it fails.
> 
> Cc: stable@vger.kernel.org
> Fixes: 290c4a902b79 ("RDMA/rxe: Fix \"Replace mr by rkey in responder resources\"")
> Signed-off-by: WenTao Liang <vulab@iscas.ac.cn>
> ---
>   drivers/infiniband/sw/rxe/rxe_resp.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c b/drivers/infiniband/sw/rxe/rxe_resp.c
> index 9cb2f6fbf2dd..0c3f3930b494 100644
> --- a/drivers/infiniband/sw/rxe/rxe_resp.c
> +++ b/drivers/infiniband/sw/rxe/rxe_resp.c
> @@ -514,7 +514,12 @@ static enum resp_states check_rkey(struct rxe_qp *qp,
>   		if (mw->access & IB_ZERO_BASED)
>   			qp->resp.offset = mw->addr;
>   
> -		rxe_get(mr);
> +		if (!rxe_get(mr)) {

Can you reproduce this (rxe_get(mr) = 0)?

Thanks a lot.

Zhu Yanjun

> +			rxe_put(mw);
> +			mw = NULL;
> +			state = get_rkey_violation_state(pkt);
> +			goto err;
> +		}
>   		rxe_put(mw);
>   		mw = NULL;
>   	} else {