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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1783691099; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=B6VmVXS+DVJ0n101ho+JP1JR0MasVN8LbWr//fjD4SM=; b=iNz67jaCYSmR8BA/vntbPP0t/0uWJsEwXKasUcaCpth5KVfmPxToOH40X6vU2Flveq93k7 KHPP1VLjfqUgAPxUG8Jy9LDsnjEj17zaBPOvj3seYWCRCQFBWWRfMMxKifKJu0prjRU9Aa UW7YOoBHmpIkkEfotwdxO08evtAr4W8= X-MC-Unique: MDr7OEBXOk-HvE6IQ-qHXw-1 X-Mimecast-MFC-AGG-ID: MDr7OEBXOk-HvE6IQ-qHXw_1783691097 From: marcandre.lureau@redhat.com To: qemu-devel@nongnu.org Cc: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= Subject: [PATCH] hw/display/qxl: fix heap buffer overflow in qxl_blit Date: Fri, 10 Jul 2026 17:44:50 +0400 Message-ID: <20260710134450.2314872-1-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: 8 X-Spam_score: 0.8 X-Spam_bar: / X-Spam_report: (0.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, 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_H3=0.001, RCVD_IN_MSPIKE_WL=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: 1783691118675158500 From: Marc-Andr=C3=A9 Lureau qxl_blit() used the guest-controlled abs_stride to walk the destination display surface pointer. When the guest sets a negative stride, the display surface is allocated with qemu_create_displaysurface() using width-based stride, but abs_stride can be much larger (e.g. 65536 for width=3D64). This causes dst to advance past the allocated surface buffer, resulting in an out-of-bounds heap write with attacker-controlled bytes. Use surface_stride() for the destination pointer instead, which returns the actual stride of the allocated display surface. When stride > 0 the surface is created with abs_stride so behavior is unchanged. Fixes: CVE-2026-15251 Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3813 Reported-by: Pulkit Singh Singaria (x3ero0) Signed-off-by: Marc-Andr=C3=A9 Lureau --- hw/display/qxl-render.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/hw/display/qxl-render.c b/hw/display/qxl-render.c index 4799c9e8bef..3f922f5c170 100644 --- a/hw/display/qxl-render.c +++ b/hw/display/qxl-render.c @@ -30,6 +30,7 @@ static void qxl_blit(PCIQXLDevice *qxl, QXLRect *rect) uint8_t *dst =3D surface_data(surface); uint8_t *src; int len, i; + int dst_stride =3D surface_stride(surface); =20 if (!surface_is_allocated(surface)) { return; @@ -45,14 +46,14 @@ static void qxl_blit(PCIQXLDevice *qxl, QXLRect *rect) } else { src +=3D rect->top * qxl->guest_primary.abs_stride; } - dst +=3D rect->top * qxl->guest_primary.abs_stride; + dst +=3D rect->top * dst_stride; src +=3D rect->left * qxl->guest_primary.bytes_pp; dst +=3D rect->left * qxl->guest_primary.bytes_pp; len =3D (rect->right - rect->left) * qxl->guest_primary.bytes_pp; =20 for (i =3D rect->top; i < rect->bottom; i++) { memcpy(dst, src, len); - dst +=3D qxl->guest_primary.abs_stride; + dst +=3D dst_stride; src +=3D qxl->guest_primary.qxl_stride; } } --=20 2.55.0