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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Apr 23, 2026 at 07:33:07AM +0200, Michal Pecio wrote:
> 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,

That's the best thing to do.

thanks,

greg k-h