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From: Peter Maydell <peter.maydell@linaro.org>
Date: Sat, 9 Mar 2019 14:08:36 +0000
Message-ID: <CAFEAcA-AJYJZxRfcFz0mV6uF9jy4g+heL-Y-DR_nbNVS=AwoqA@mail.gmail.com>
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Subject: Re: [Qemu-devel] [PULL 3/4] usb-mtp: prevent null dereference while
 deleting objects
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To: Bandan Das <bsd@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>

On Fri, 8 Mar 2019 at 19:46, Bandan Das <bsd@redhat.com> wrote:
> This is very broken! I think something like this should work:
> diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c
> index 06e376bcd2..87a4bfb415 100644
> --- a/hw/usb/dev-mtp.c
> +++ b/hw/usb/dev-mtp.c
> @@ -1138,8 +1138,8 @@ static MTPData *usb_mtp_get_object_prop_value(MTPState *s, MTPControl *c,
>  /* Return correct return code for a delete event */
>  enum {
>      ALL_DELETE,
> -    PARTIAL_DELETE,
>      READ_ONLY,
> +    PARTIAL_DELETE,
>  };

This is defining these values as an incrementing series...


>      if (o->format == FMT_UNDEFINED_OBJECT) {
>          if (remove(o->path)) {
> -            partial_delete = true;
> +            ret |= READ_ONLY;
>          } else {
>              usb_mtp_object_free_one(s, o);
> -            success = true;
> +            ret |= ALL_DELETE;

...but here we're using them as bits which we OR together.
In particular ALL_DELETE is 0, so ORing it in will
do nothing.

thanks
-- PMM