Re: [PATCH] xhci: fix null pointer deref for xhci_urb_enqueue

[Mathias Nyman]

On 20.11.2023 17.33, Mathias Nyman wrote:
> On 18.11.2023 12.19, Kuen-Han Tsai wrote:
> > Hi Mathias
> >
> > > >        if (usb_endpoint_xfer_isoc(&urb->ep->desc))
> > > > @@ -1552,8 +1561,10 @@ static int xhci_urb_enqueue(struct usb_hcd *hcd, struct urb *urb, gfp_t mem_flag
> > > >                num_tds = 1;
> > > >
> > > >        urb_priv = kzalloc(struct_size(urb_priv, td, num_tds), mem_flags);
> > > kzalloc with spinlock held, should preferably be moved outside lock, otherwise should use GFP_ATOMIC
> >
> > Thanks for pointing this out. I realize this patch is incorrect and it
> > is non-ideal to include many codes unrelated to xhci->devs[slot_id]
> > within the lock.
> >
> > > xhci_check_maxpacket() called here can't be called with spinlock held
> >
> > It appears that xhci_check_maxpacket() might potentially lead to a
> > deadlock later if a spinlock is held. Is this the concern you were
> > referring to? If not, please let me know if there are any other
> > potential issues that I may have missed, thanks!
>
> xhci_check_maxpacket() will allocate memory, wait for completion, and use the same lock,
> so there are several issues here.
>
> I actually think we shouldn't call xhci_check_maxpacket() at all while queuing urbs.
>
> usb core knows when there was max packet size mismatch during enumeration.
> I think we should add a hook to the hcd that usb core can call in these cases

I moved the max packet checks away from xhci_urb_enqueue() and fixed up the locking.

I can't trigger the original issue, but I tested it by setting incorrect initial max packet
size values.

If you have the chance to test this with your setup I'd appreciate it.

patches found here:
git://git.kernel.org/pub/scm/linux/kernel/git/mnyman/xhci.git fix_urb_enqueue_locking
https://git.kernel.org/pub/scm/linux/kernel/git/mnyman/xhci.git/log/?h=fix_urb_enqueue_locking

I'll add them to this thread as well

thanks
Mathias