Re: [PATCH] RDMA/rxe: Reject prefetch of a non-ODP MR

[Leon Romanovsky]

On Thu, Aug 27, 2026 at 12:51:20PM +0200, Norbert Szetei wrote:
> rxe_ib_advise_mr_prefetch() and rxe_ib_prefetch_sg_list() look up the MR
> by lkey and hand it to rxe_odp_do_pagefault_and_lock() without checking
> that it is an ODP MR. That path runs to_ib_umem_odp() on mr->umem, and
> for a non-ODP MR mr->umem is a plain struct ib_umem from ib_umem_get(),
> so the container_of() in to_ib_umem_odp() lands past the end of the
> object and ib_umem_odp_map_dma_and_lock() reads its ib_umem_odp fields
> out of bounds.
> 
> lookup_mr() validates the lkey, PD, access and state but not the MR
> type, and IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH is accepted for any MR.
> 
>   BUG: KASAN: slab-out-of-bounds in ib_umem_odp_map_dma_and_lock+0x884/0x8a0
>   Read of size 8 at addr ffff88810a3ebcf0 by task advi/921
>    ib_umem_odp_map_dma_and_lock+0x884/0x8a0
>    rxe_ib_advise_mr+0x543/0xad0
>    ib_uverbs_handler_UVERBS_METHOD_ADVISE_MR+0x446/0x530
>    ib_uverbs_cmd_verbs+0x2b3c/0x3b20
>    ib_uverbs_ioctl+0x1e3/0x310
>   Allocated by task 921:
>    __ib_umem_get_va+0x13e/0xae0
>    rxe_mr_init_user+0x2ae/0xb00
>    rxe_reg_user_mr+0x337/0x510
>   The buggy address belongs to the object at ffff88810a3ebc80
>    which belongs to the cache kmalloc-96 of size 96
> 
> Reject a non-ODP MR after lookup_mr() in both the synchronous and
> asynchronous prefetch arms.
> 
> Fixes: 3576b0df1588 ("RDMA/rxe: Implement synchronous prefetch for ODP MRs")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Norbert Szetei <norbert@xxxxxxxxxxxx>
> ---
>  drivers/infiniband/sw/rxe/rxe_odp.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/infiniband/sw/rxe/rxe_odp.c b/drivers/infiniband/sw/rxe/rxe_odp.c
> index e870efa7a0a3..5c9dde3501a0 100644
> --- a/drivers/infiniband/sw/rxe/rxe_odp.c
> +++ b/drivers/infiniband/sw/rxe/rxe_odp.c
> @@ -472,6 +472,11 @@ static int rxe_ib_prefetch_sg_list(struct ib_pd *ibpd,
>  			return -EINVAL;
>  		}
>  
> +		if (unlikely(!is_odp_mr(mr))) {
> +			rxe_put(mr);
> +			return -EOPNOTSUPP;
> +		}

The idea is correct, but the implementation needs some improvement.

RXE stores the access flags in the MR, including IB_ACCESS_ON_DEMAND,
which indicates that the MR was created as an ODP MR. lookup_mr()
should check this flag and perform the lookup accordingly.

Thanks.