From: Paolo Bonzini <pbonzini@redhat.com>
To: qemu-devel@nongnu.org
Cc: lersek@redhat.com, Gerd Hoffmann <kraxel@redhat.com>
Subject: [Qemu-devel] [PATCH v2] cirrus_vga: fix off-by-one in blit_region_is_unsafe
Date: Wed, 10 Feb 2016 17:17:39 +0100 [thread overview]
Message-ID: <1455121059-18280-1-git-send-email-pbonzini@redhat.com> (raw)
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;
}
}
--
2.5.0
next reply other threads:[~2016-02-10 16:17 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-10 16:17 Paolo Bonzini [this message]
2016-02-10 16:54 ` [Qemu-devel] [PATCH v2] cirrus_vga: fix off-by-one in blit_region_is_unsafe Laszlo Ersek
2016-02-16 13:30 ` Gerd Hoffmann
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