Re: [PATCH] usb: usbtmc: Allocate enough space for interrupt-IN buffer

[Michal Pecio <michal.pecio@gmail.com>]

On Wed, 22 Apr 2026 19:22:09 -0300, Heitor Alves de Siqueira wrote:
> The USBTMC driver allocates the Interrupt-IN buffer according to the
> wMaxPacketSize value obtained from the USB endpoint. If a USB device
> advertises a small enough wMaxPacketSize (e.g. a malfunctioning device
> or an endpoint constructed by syzbot), the buffer will not have enough
> space for the mandatory headers and will trigger an out-of-bounds read.
> 
> Fix by ensuring the driver will allocate at least enough space to fit
> the headers for Interrupt-IN packets (bNotify1 and bNotify2).
> 
> Fixes: dbf3e7f654c0 ("Implement an ioctl to support the USMTMC-USB488 READ_STATUS_BYTE operation.")
> Reported-by: syzbot+abbfd103085885cf16a2@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=abbfd103085885cf16a2
> Cc: stable@kernel.org
> Signed-off-by: Heitor Alves de Siqueira <halves@igalia.com>
> ---
>  drivers/usb/class/usbtmc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
> index bd9347804dec..22efa74008f8 100644
> --- a/drivers/usb/class/usbtmc.c
> +++ b/drivers/usb/class/usbtmc.c
> @@ -2452,7 +2452,7 @@ static int usbtmc_probe(struct usb_interface *intf,
>  		kref_get(&data->kref);
>  
>  		/* allocate buffer for interrupt in */
> -		data->iin_buffer = kmalloc(data->iin_wMaxPacketSize,
> +		data->iin_buffer = kmalloc(max(2, data->iin_wMaxPacketSize),
>  					GFP_KERNEL);

This changes OOB read into uninitialized memory read, which syzbot
may complain about again next week.

More reliable fix would be to reject such devices if they are illegal,
or make the driver not read beyond wMaxPacketSize if they are legal.

Note that the driver never worked for them properly anyway and returned
data from unititialized memory or page faulted.

>  		if (!data->iin_buffer) {
>  			retcode = -ENOMEM;
> 
> ---
> base-commit: 70c8a7ec6715b5fb14e501731b5b9210a16684f7
> change-id: 20260422-usbtmc-iin-size-f1aaf04a6c4c
> 
> Best regards,
> --  
> Heitor Alves de Siqueira <halves@igalia.com>
>