Re: [Qemu-devel] [PATCH v3] cirrus: fix oob access issue (CVE-2017-2615)

[Laszlo Ersek <lersek@redhat.com>]

On 02/01/17 09:35, Gerd Hoffmann wrote:
> From: Li Qiang <liqiang6-s@360.cn>
> 
> When doing bitblt copy in backward mode, we should minus the
> blt width first just like the adding in the forward mode. This
> can avoid the oob access of the front of vga's vram.
> 
> Signed-off-by: Li Qiang <liqiang6-s@360.cn>
> Message-id: 5887254f.863a240a.2c122.5500@mx.google.com
> 
> { kraxel: with backward blits (negative pitch) addr is the topmost
>           address, so check it as-is against vram size ]
> 
> Cc: qemu-stable@nongnu.org
> Cc: P J P <ppandit@redhat.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Wolfgang Bumiller <w.bumiller@proxmox.com>
> Fixes: d3532a0db02296e687711b8cdc7791924efccea0 (CVE-2014-8106)
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  hw/display/cirrus_vga.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
> index 95873ae..3961712 100644
> --- a/hw/display/cirrus_vga.c
> +++ b/hw/display/cirrus_vga.c
> @@ -277,10 +277,9 @@ static bool blit_region_is_unsafe(struct CirrusVGAState *s,
>      }
>      if (pitch < 0) {
>          int64_t min = addr
> -            + ((int64_t)s->cirrus_blt_height-1) * pitch;
> -        int32_t max = addr
> -            + s->cirrus_blt_width;
> -        if (min < 0 || max > s->vga.vram_size) {
> +            + ((int64_t)s->cirrus_blt_height - 1) * pitch
> +            - s->cirrus_blt_width;
> +        if (min < -1 || addr >= s->vga.vram_size) {
>              return true;
>          }
>      } else {
> 

Famous last words:

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Thanks
Laszlo