Re: [PATCH] usb: fix setup_len init (CVE-2020-14364)

[Li Qiang]

Gerd Hoffmann <kraxel@redhat.com> 于2020年8月25日周二 下午1:37写道：
>
> Store calculated setup_len in a local variable, verify it, and only
> write it to the struct (USBDevice->setup_len) in case it passed the
> sanity checks.
>
> This prevents other code (do_token_{in,out} functions specifically)
> from working with invalid USBDevice->setup_len values and overrunning
> the USBDevice->setup_buf[] buffer.
>
> Fixes: CVE-2020-14364
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> Tested-by: Gonglei <arei.gonglei@huawei.com>

Reviewed-by: Li Qiang <liq3ea@gmail.com>

Just see the page.
-->https://access.redhat.com/security/cve/CVE-2020-14364

The 'Attack Vector' of the CVSS score here is 'local'.

Hi Prasad,
I think this should be 'network' as the guest user can touch this in
cloud environment?
What's the consideration here?

Thanks,
Li Qiang

> ---
>  hw/usb/core.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/hw/usb/core.c b/hw/usb/core.c
> index 5abd128b6bc5..5234dcc73fea 100644
> --- a/hw/usb/core.c
> +++ b/hw/usb/core.c
> @@ -129,6 +129,7 @@ void usb_wakeup(USBEndpoint *ep, unsigned int stream)
>  static void do_token_setup(USBDevice *s, USBPacket *p)
>  {
>      int request, value, index;
> +    unsigned int setup_len;
>
>      if (p->iov.size != 8) {
>          p->status = USB_RET_STALL;
> @@ -138,14 +139,15 @@ static void do_token_setup(USBDevice *s, USBPacket *p)
>      usb_packet_copy(p, s->setup_buf, p->iov.size);
>      s->setup_index = 0;
>      p->actual_length = 0;
> -    s->setup_len   = (s->setup_buf[7] << 8) | s->setup_buf[6];
> -    if (s->setup_len > sizeof(s->data_buf)) {
> +    setup_len = (s->setup_buf[7] << 8) | s->setup_buf[6];
> +    if (setup_len > sizeof(s->data_buf)) {
>          fprintf(stderr,
>                  "usb_generic_handle_packet: ctrl buffer too small (%d > 
> %zu)\n",
> -                s->setup_len, sizeof(s->data_buf));
> +                setup_len, sizeof(s->data_buf));
>          p->status = USB_RET_STALL;
>          return;
>      }
> +    s->setup_len = setup_len;
>
>      request = (s->setup_buf[0] << 8) | s->setup_buf[1];
>      value   = (s->setup_buf[3] << 8) | s->setup_buf[2];
> @@ -259,26 +261,28 @@ static void do_token_out(USBDevice *s, USBPacket *p)
>  static void do_parameter(USBDevice *s, USBPacket *p)
>  {
>      int i, request, value, index;
> +    unsigned int setup_len;
>
>      for (i = 0; i < 8; i++) {
>          s->setup_buf[i] = p->parameter >> (i*8);
>      }
>
>      s->setup_state = SETUP_STATE_PARAM;
> -    s->setup_len   = (s->setup_buf[7] << 8) | s->setup_buf[6];
>      s->setup_index = 0;
>
>      request = (s->setup_buf[0] << 8) | s->setup_buf[1];
>      value   = (s->setup_buf[3] << 8) | s->setup_buf[2];
>      index   = (s->setup_buf[5] << 8) | s->setup_buf[4];
>
> -    if (s->setup_len > sizeof(s->data_buf)) {
> +    setup_len = (s->setup_buf[7] << 8) | s->setup_buf[6];
> +    if (setup_len > sizeof(s->data_buf)) {
>          fprintf(stderr,
>                  "usb_generic_handle_packet: ctrl buffer too small (%d > 
> %zu)\n",
> -                s->setup_len, sizeof(s->data_buf));
> +                setup_len, sizeof(s->data_buf));
>          p->status = USB_RET_STALL;
>          return;
>      }
> +    s->setup_len = setup_len;
>
>      if (p->pid == USB_TOKEN_OUT) {
>          usb_packet_copy(p, s->data_buf, s->setup_len);
> --
> 2.27.0
>
>