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Date:   Wed, 12 May 2021 08:24:28 +0200
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Tong Zhang <ztong0001@gmail.com>
Cc:     Arnd Bergmann <arnd@arndb.de>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] misc: alcor_pci: fix null-ptr-deref when there is no
 PCI bridge
Message-ID: <YJt0nI8lG+2juL5S@kroah.com>
References: <YJrFib6BD8JcX3DM@kroah.com>
 <20210511212937.1269191-1-ztong0001@gmail.com>
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On Tue, May 11, 2021 at 05:29:38PM -0400, Tong Zhang wrote:
> Device might be attached to root complex directly. In this case,
> bus->self(bridge) will be NULL, so we'd better check before use it
> 
> [    1.246492] BUG: kernel NULL pointer dereference, address: 00000000000000c0
> [    1.248731] RIP: 0010:pci_read_config_byte+0x5/0x40
> [    1.253998] Call Trace:
> [    1.254131]  ? alcor_pci_find_cap_offset.isra.0+0x3a/0x100 [alcor_pci]
> [    1.254476]  alcor_pci_probe+0x169/0x2d5 [alcor_pci]
> 
> Signed-off-by: Tong Zhang <ztong0001@gmail.com>
> Co-Developed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> v2: check before calling alcor_pci_find_cap_offset()
> 
>  drivers/misc/cardreader/alcor_pci.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/misc/cardreader/alcor_pci.c b/drivers/misc/cardreader/alcor_pci.c
> index cd402c89189e..175c6b06f7aa 100644
> --- a/drivers/misc/cardreader/alcor_pci.c
> +++ b/drivers/misc/cardreader/alcor_pci.c
> @@ -139,6 +139,9 @@ static void alcor_pci_init_check_aspm(struct alcor_pci_priv *priv)
>  	u32 val32;
>  
>  	priv->pdev_cap_off    = alcor_pci_find_cap_offset(priv, priv->pdev);
> +
> +	if (!priv->parent_pdev)
> +		return;

That feels wrong, you just prevented all of the remaining logic in this
call to not be set up.  Did you test this and did the driver and device
still work properly if it hits this check?

thanks,

greg k-h