| Message ID | 1455121059-18280-1-git-send-email-pbonzini@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 02/10/16 17:17, Paolo Bonzini wrote: > The "max" value is being compared with >=, but addr + width points to > the first byte that will _not_ be copied. Laszlo suggested using a > "greater than" comparison, instead of subtracting one like it is > already done above for the height, so that max remains always positive. > > The mistake is "safe"---it will reject some blits, but will never cause > out-of-bounds writes. > > Cc: Gerd Hoffmann <kraxel@redhat.com> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > hw/display/cirrus_vga.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c > index b6ce1c8..57b91a7 100644 > --- a/hw/display/cirrus_vga.c > +++ b/hw/display/cirrus_vga.c > @@ -276,14 +276,14 @@ static bool blit_region_is_unsafe(struct CirrusVGAState *s, > + ((int64_t)s->cirrus_blt_height-1) * pitch; > int32_t max = addr > + s->cirrus_blt_width; > - if (min < 0 || max >= s->vga.vram_size) { > + if (min < 0 || max > s->vga.vram_size) { > return true; > } > } else { > int64_t max = addr > + ((int64_t)s->cirrus_blt_height-1) * pitch > + s->cirrus_blt_width; > - if (max >= s->vga.vram_size) { > + if (max > s->vga.vram_size) { > return true; > } > } > Thank you for your patience. :) Reviewed-by: Laszlo Ersek <lersek@redhat.com>
On Mi, 2016-02-10 at 17:17 +0100, Paolo Bonzini wrote: > The "max" value is being compared with >=, but addr + width points to > the first byte that will _not_ be copied. Laszlo suggested using a > "greater than" comparison, instead of subtracting one like it is > already done above for the height, so that max remains always > positive. > > The mistake is "safe"---it will reject some blits, but will never > cause > out-of-bounds writes. added to vga queue. thanks, Gerd
diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c index b6ce1c8..57b91a7 100644 --- a/hw/display/cirrus_vga.c +++ b/hw/display/cirrus_vga.c @@ -276,14 +276,14 @@ static bool blit_region_is_unsafe(struct CirrusVGAState *s, + ((int64_t)s->cirrus_blt_height-1) * pitch; int32_t max = addr + s->cirrus_blt_width; - if (min < 0 || max >= s->vga.vram_size) { + if (min < 0 || max > s->vga.vram_size) { return true; } } else { int64_t max = addr + ((int64_t)s->cirrus_blt_height-1) * pitch + s->cirrus_blt_width; - if (max >= s->vga.vram_size) { + if (max > s->vga.vram_size) { return true; } }
The "max" value is being compared with >=, but addr + width points to the first byte that will _not_ be copied. Laszlo suggested using a "greater than" comparison, instead of subtracting one like it is already done above for the height, so that max remains always positive. The mistake is "safe"---it will reject some blits, but will never cause out-of-bounds writes. Cc: Gerd Hoffmann <kraxel@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- hw/display/cirrus_vga.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)