Re: [PATCH net v2] net: devmem: reject dma-buf bind with non-page-aligned size or SG length

[Stanislav Fomichev <sdf.kernel@gmail.com>]

On 05/19, David Carlier wrote:
> net_devmem_bind_dmabuf() trusts dmabuf->size and sg_dma_len() to be
> PAGE_SIZE multiples without checking:
> 
>   - tx_vec is sized dmabuf->size / PAGE_SIZE, and
>     net_devmem_get_niov_at() only bounds-checks virt_addr < dmabuf->size
>     before indexing tx_vec[virt_addr / PAGE_SIZE]. With size =
>     N*PAGE_SIZE + r (1 <= r < PAGE_SIZE), sendmsg() at iov_base =
>     N*PAGE_SIZE passes the bound check and reads tx_vec[N] -- one past.
> 
>   - owner->area.num_niovs = len / PAGE_SIZE while gen_pool_add_owner()
>     covers the full byte len, so a non-page-multiple non-final sg
>     desyncs num_niovs from the gen_pool region for every later sg, on
>     both RX and TX.
> 
> dma-buf does not require page-aligned sizes, so the bind path has to
> enforce what its own indexing assumes. Reject both with -EINVAL.
> 
> The size check is TX-only (only tx_vec is sized off dmabuf->size); the
> SG-length check covers both directions.
> 
> Fixes: bd61848900bf ("net: devmem: Implement TX path")
> Cc: stable@vger.kernel.org
> Signed-off-by: David Carlier <devnexen@gmail.com>
> ---
> Changes in v2:
>   - Reframe commit message around the kernel-side OOB instead of
>     "real exporters already page-align", which read as the OOB being
>     unreachable and undercut Cc: stable (Stanislav Fomichev).
>   - Hoist the SG-length check out of the if (TX) branch so it covers
>     RX too; RX has the same num_niovs / gen_pool desync on a
>     contract-violating exporter, just without an OOB. Keep the
>     size-multiple check TX-only (Stanislav Fomichev).
>   - Drop bool todevice; compare direction == DMA_TO_DEVICE inline to
>     match the existing call site at the tx_vec[] assignment
>     (Bobby Eshleman).

Acked-by: Stanislav Fomichev <sdf@fomichev.me>

Thanks!