Re: [PULL 4/6] usb/redir: avoid dynamic stack allocation (CVE-2021-3527)

[Remy Noel]

On Wed, May 05, 2021 at 03:07:14PM +0200, Gerd Hoffmann wrote:
> [...]
> diff --git a/hw/usb/redirect.c b/hw/usb/redirect.c
> index 17f06f34179a..6a75b0dc4ab2 100644
> --- a/hw/usb/redirect.c
> +++ b/hw/usb/redirect.c
> @@ -620,7 +620,7 @@ static void usbredir_handle_iso_data(USBRedirDevice *dev, 
> USBPacket *p,
>                 .endpoint = ep,
>                 .length = p->iov.size
>             };
> -            uint8_t buf[p->iov.size];
> +            g_autofree uint8_t *buf = g_malloc(p->iov.size);
>             /* No id, we look at the ep when receiving a status back */
>             usb_packet_copy(p, buf, p->iov.size);
>             usbredirparser_send_iso_packet(dev->parser, 0, &iso_packet,
> @@ -818,7 +818,7 @@ static void usbredir_handle_bulk_data(USBRedirDevice *dev, 
> USBPacket *p,
>         usbredirparser_send_bulk_packet(dev->parser, p->id,
>                                         &bulk_packet, NULL, 0);
>     } else {
> -        uint8_t buf[size];
> +        g_autofree uint8_t *buf = g_malloc(size);
>         usb_packet_copy(p, buf, size);

Won't this allows us to malloc then write an arbitrary amount of heap 
memory, allowing a guest driver to abort the qemu ?

Remy