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Tsirkin" Subject: [PATCH] hw/display/virtio-gpu: fix offset truncation in scanout_blob_to_fb Date: Fri, 24 Jul 2026 08:01:26 +0400 Message-ID: <20260724040126.867935-1-marcandre.lureau@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists1p.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=marcandre.lureau@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 3 X-Spam_score: 0.3 X-Spam_bar: / X-Spam_report: (0.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.951, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1784865725323158500 From: Marc-Andr=C3=A9 Lureau virtio_gpu_scanout_blob_to_fb() computes the framebuffer offset from guest-controlled offsets[0], r.x, r.y and stride using uint32_t arithmetic. The sum can wrap around, so a small fb->offset passes the fbend > blob_size check even though the real offset lies outside the blob. The wrapped value is later used as data + fb->offset in virtio_gpu_do_set_scanout(), letting the guest point the scanout at host memory beyond the blob. Compute the offset in uint64_t, reject values wider than UINT32_MAX (the width of fb->offset), and only store into fb->offset once both range checks pass. Fixes: CVE-2026-66019 Fixes: 32db3c63ae11 ("virtio-gpu: Add virtio_gpu_set_scanout_blob") Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3871 Reported-by: Cyber_black Signed-off-by: Marc-Andr=C3=A9 Lureau --- hw/display/virtio-gpu.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c index 36d2bd9edee6..d1e32840e223 100644 --- a/hw/display/virtio-gpu.c +++ b/hw/display/virtio-gpu.c @@ -784,7 +784,7 @@ bool virtio_gpu_scanout_blob_to_fb(struct virtio_gpu_fr= amebuffer *fb, struct virtio_gpu_set_scanout_blob *ss, uint64_t blob_size) { - uint64_t fbend; + uint64_t fbend, offset; uint32_t bytes_pp; =20 fb->format =3D virtio_gpu_get_pixman_format(ss->format); @@ -814,18 +814,20 @@ bool virtio_gpu_scanout_blob_to_fb(struct virtio_gpu_= framebuffer *fb, return false; } =20 - fb->offset =3D ss->offsets[0] + ss->r.x * bytes_pp + ss->r.y * fb->str= ide; + offset =3D (uint64_t)ss->offsets[0] + (uint64_t)ss->r.x * bytes_pp + + (uint64_t)ss->r.y * fb->stride; =20 - fbend =3D fb->offset; - fbend +=3D (uint64_t) fb->stride * ss->r.height; + fbend =3D offset + (uint64_t)fb->stride * ss->r.height; =20 - if (fbend > blob_size) { + if (offset > UINT32_MAX || fbend > blob_size) { qemu_log_mask(LOG_GUEST_ERROR, - "%s: fb end out of range\n", + "%s: invalid fb bounds\n", __func__); return false; } =20 + fb->offset =3D offset; + return true; } =20 --=20 2.55.0