linux-kernel - Re: [PATCH net-next v1] net: devmem: NULL check netdev_nl_get_dma

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Message-ID: <CAHS8izMnwZkQ7pDpSyf2tviQrniWPv8nat6ucaZHsfqm6Er=gA@mail.gmail.com>
Date: Fri, 29 Aug 2025 15:02:18 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Dragos Tatulea <dtatulea@...dia.com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Joe Damato <jdamato@...tly.com>, Stanislav Fomichev <sdf@...ichev.me>
Subject: Re: [PATCH net-next v1] net: devmem: NULL check netdev_nl_get_dma_dev
 return value

Missed ccing Dragos. Adding manually.

On Fri, Aug 29, 2025 at 3:00 PM Mina Almasry <almasrymina@...gle.com> wrote:
>
> netdev_nl_get_dma_dev can return NULL. This happens in the unlikely
> scenario that netdev->dev.parent is NULL, or all the calls to the
> ndo_queue_get_dma_dev return NULL from the driver.
>
> Current code doesn't NULL check the return value, so it may be passed to
> net_devmem_bind_dmabuf, which AFAICT will eventually hit
> WARN_ON(!dmabuf || !dev) in dma_buf_dynamic_attach and do a kernel
> splat. Avoid this scenario by using IS_ERR_OR_NULL in place of IS_ERR.
>
> Found by code inspection.
>
> Note that this was a problem even before the fixes patch, since we
> passed netdev->dev.parent to net_devmem_bind_dmabuf before NULL checking
> it anyway :( But that code got removed in the fixes patch (and retained
> the bug).
>
> Fixes: b8aab4bb9585 ("net: devmem: allow binding on rx queues with same DMA devices")
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
>
> ---
>  net/core/netdev-genl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> index 470fabbeacd9..779bcdb5653d 100644
> --- a/net/core/netdev-genl.c
> +++ b/net/core/netdev-genl.c
> @@ -1098,7 +1098,7 @@ int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info)
>         dma_dev = netdev_queue_get_dma_dev(netdev, 0);
>         binding = net_devmem_bind_dmabuf(netdev, dma_dev, DMA_TO_DEVICE,
>                                          dmabuf_fd, priv, info->extack);
> -       if (IS_ERR(binding)) {
> +       if (IS_ERR_OR_NULL(binding)) {
>                 err = PTR_ERR(binding);
>                 goto err_unlock_netdev;
>         }
>
> base-commit: 4f54dff818d7b5b1d84becd5d90bc46e6233c0d7
> --
> 2.51.0.318.gd7df087d1a-goog
>


-- 
Thanks,
Mina