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

[Leon Romanovsky]

On Fri, Sep 04, 2026 at 09:49:26AM +0200, Norbert Szetei wrote:
> On Sep 1, 2026, at 09:56, Leon Romanovsky <leon@xxxxxxxxxx> wrote:
> > 
> > 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.
> 
> Do you mean lookup_mr() should take IB_ACCESS_ON_DEMAND into account, so that
> the existing (access & mr->access) != access test rejects the non-ODP MR?

I expected lookup_mr(..., IB_ACCESS_ON_DEMAND) to be called and to
perform all the necessary checks internally.

> 
> rxe_rereg_user_mr() with IB_MR_REREG_ACCESS assigns mr->access directly, and
> IB_ACCESS_ON_DEMAND is part of RXE_ACCESS_SUPPORTED_MR. So userspace can set
> that flag on a plain MR after registration, without the umem changing. Am I
> missing something there?

I assume this is a bug that needs to be fixed.

Thanks

> 
> Thanks.
> 
> > 
> > Thanks.
> 
>