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SubjectRe: [PATCH 5.10 26/76] sfc: Check null pointer of rx_queue->page_ring
On Wed, Dec 29, 2021 at 12:17:30PM +0100, Pavel Machek wrote:
> hi!
>
> > From: Jiasheng Jiang <jiasheng@iscas.ac.cn>
> >
> > [ Upstream commit bdf1b5c3884f6a0dc91b0dbdb8c3b7d205f449e0 ]
> >
> > Because of the possible failure of the kcalloc, it should be better to
> > set rx_queue->page_ptr_mask to 0 when it happens in order to maintain
> > the consistency.
>
> This is confusing/wrong, or at least not a complete fix.
>
> > +++ b/drivers/net/ethernet/sfc/rx_common.c
> > @@ -150,7 +150,10 @@ static void efx_init_rx_recycle_ring(struct efx_rx_queue *rx_queue)
> > efx->rx_bufs_per_page);
> > rx_queue->page_ring = kcalloc(page_ring_size,
> > sizeof(*rx_queue->page_ring), GFP_KERNEL);
> > - rx_queue->page_ptr_mask = page_ring_size - 1;
> > + if (!rx_queue->page_ring)
> > + rx_queue->page_ptr_mask = 0;
> > + else
> > + rx_queue->page_ptr_mask = page_ring_size - 1;
> > }
> >
>
> So we have !rx_queue->page_ring. But in efx_reuse_page, we do
>
> index = rx_queue->page_remove & rx_queue->page_ptr_mask;
> page = rx_queue->page_ring[index];
>
> So index is now zero, but we'll derefernce null pointer anyway.

Good point. I've posted a patch for this to netdev.
https://lore.kernel.org/netdev/164103678041.26263.8354809911405746465.stgit@palantir17.mph.net/

Thanks,
Martin

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