linux-kernel - Re: [PATCH v3] net/can/gs_usb: increase max interface to U8

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Message-ID: <7a2a0124-7269-40b5-a423-e4b704f51628@kernel.org>
Date: Tue, 30 Sep 2025 14:57:20 +0900
From: Vincent Mailhol <mailhol@...nel.org>
To: Celeste Liu <uwu@...lacanthus.name>
Cc: Maximilian Schneider <max@...neidersoft.net>,
 Henrik Brix Andersen <henrik@...xandersen.dk>,
 Wolfgang Grandegger <wg@...ndegger.com>, Kees Cook <kees@...nel.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>, linux-can@...r.kernel.org,
 linux-kernel@...r.kernel.org, Runcheng Lu <runcheng.lu@...icro.com>,
 stable@...r.kernel.org, Marc Kleine-Budde <mkl@...gutronix.de>
Subject: Re: [PATCH v3] net/can/gs_usb: increase max interface to U8_MAX

Hi Celeste,

Sorry, one last minute comment which I forgot in my previous message.

On 9/30/25 12:06 PM, Celeste Liu wrote:
> This issue was found by Runcheng Lu when develop HSCanT USB to CAN FD
> converter[1]. The original developers may have only 3 intefaces device to
> test so they write 3 here and wait for future change.
> 
> During the HSCanT development, we actually used 4 interfaces, so the
> limitation of 3 is not enough now. But just increase one is not
> future-proofed. Since the channel type in gs_host_frame is u8, just
> increase interface number limit to max size of u8 safely.
> 
> [1]: https://github.com/cherry-embedded/HSCanT-hardware
> 
> Fixes: d08e973a77d1 ("can: gs_usb: Added support for the GS_USB CAN devices")
> Reported-by: Runcheng Lu <runcheng.lu@...icro.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Celeste Liu <uwu@...lacanthus.name>
> ---
> Changes in v3:
> - Cc stable should in patch instead of cover letter.
> - Link to v2: https://lore.kernel.org/r/20250930-gs-usb-max-if-v2-1-2cf9a44e6861@coelacanthus.name
> 
> Changes in v2:
> - Use flexible array member instead of fixed array.
> - Link to v1: https://lore.kernel.org/r/20250929-gs-usb-max-if-v1-1-e41b5c09133a@coelacanthus.name
> ---
>  drivers/net/can/usb/gs_usb.c | 22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c
> index c9482d6e947b0c7b033dc4f0c35f5b111e1bfd92..69b068c8fa8fbab42337e2b0a3d0860ac678c792 100644
> --- a/drivers/net/can/usb/gs_usb.c
> +++ b/drivers/net/can/usb/gs_usb.c
> @@ -289,11 +289,6 @@ struct gs_host_frame {
>  #define GS_MAX_RX_URBS 30
>  #define GS_NAPI_WEIGHT 32
>  
> -/* Maximum number of interfaces the driver supports per device.
> - * Current hardware only supports 3 interfaces. The future may vary.
> - */
> -#define GS_MAX_INTF 3
> -
>  struct gs_tx_context {
>  	struct gs_can *dev;
>  	unsigned int echo_id;
> @@ -324,7 +319,6 @@ struct gs_can {
>  
>  /* usb interface struct */
>  struct gs_usb {
> -	struct gs_can *canch[GS_MAX_INTF];
>  	struct usb_anchor rx_submitted;
>  	struct usb_device *udev;
>  
> @@ -336,9 +330,11 @@ struct gs_usb {
>  
>  	unsigned int hf_size_rx;
>  	u8 active_channels;
> +	u8 channel_cnt;
>  
>  	unsigned int pipe_in;
>  	unsigned int pipe_out;
> +	struct gs_can *canch[] __counted_by(channel_cnt);
>  };
>  
>  /* 'allocate' a tx context.
> @@ -599,7 +595,7 @@ static void gs_usb_receive_bulk_callback(struct urb *urb)
>  	}
>  
>  	/* device reports out of range channel id */
> -	if (hf->channel >= GS_MAX_INTF)
> +	if (hf->channel >= parent->channel_cnt)
>  		goto device_detach;
>  
>  	dev = parent->canch[hf->channel];
> @@ -699,7 +695,7 @@ static void gs_usb_receive_bulk_callback(struct urb *urb)
>  	/* USB failure take down all interfaces */
>  	if (rc == -ENODEV) {
>  device_detach:
> -		for (rc = 0; rc < GS_MAX_INTF; rc++) {
> +		for (rc = 0; rc < parent->channel_cnt; rc++) {
>  			if (parent->canch[rc])
>  				netif_device_detach(parent->canch[rc]->netdev);
>  		}
> @@ -1460,17 +1456,19 @@ static int gs_usb_probe(struct usb_interface *intf,
>  	icount = dconf.icount + 1;
>  	dev_info(&intf->dev, "Configuring for %u interfaces\n", icount);
>  
> -	if (icount > GS_MAX_INTF) {
> +	if (icount > type_max(typeof(parent->channel_cnt))) {
                              ^^^^^^
If you send a v4 to fix the typo, can you also remove this typeof()?

It used to be required, but this is not the case anymore since commit
bd1ebf2467f9 ("overflow: Allow non-type arg to type_max() and type_min()").

(my Reviewed-by tag is still valid).

>  		dev_err(&intf->dev,
>  			"Driver cannot handle more that %u CAN interfaces\n",
> -			GS_MAX_INTF);
> +			type_max(typeof(parent->channel_cnt)));
                                 ^^^^^^
same

>  		return -EINVAL;
>  	}
>  
> -	parent = kzalloc(sizeof(*parent), GFP_KERNEL);
> +	parent = kzalloc(struct_size(parent, canch, icount), GFP_KERNEL);
>  	if (!parent)
>  		return -ENOMEM;
>  
> +	parent->channel_cnt = icount;
> +
>  	init_usb_anchor(&parent->rx_submitted);
>  
>  	usb_set_intfdata(intf, parent);
> @@ -1531,7 +1529,7 @@ static void gs_usb_disconnect(struct usb_interface *intf)
>  		return;
>  	}
>  
> -	for (i = 0; i < GS_MAX_INTF; i++)
> +	for (i = 0; i < parent->channel_cnt; i++)
>  		if (parent->canch[i])
>  			gs_destroy_candev(parent->canch[i]);


-- 
Yours sincerely,
Vincent Mailhol