[QEMU HCI-8.0 PATCH 3/7] hw/display/qxl: Fix mono cursor validation that can read past a cursor chunk #VSTOR-144000

["Denis V. Lunev" <den@openvz.org>]

From: Thomas Huth <thuth@redhat.com>

qxl_render_cursor() maps the guest-provided QXLCursor object using the
guest-controlled cursor->chunk.data_size.
For a mono cursor, qxl_cursor() then validates the expected bitmap size
against cursor->data_size, but it does not validate that the first chunk
actually contains that many bytes.
A guest could set cursor->data_size to the correct full mono cursor size
while setting cursor->chunk.data_size to zero. In that case, cursor_set_mono()
reads the AND/XOR masks starting at cursor->chunk.data. If the cursor object
is placed at the end of the QXL RAM BAR, those reads cross the mapped RAM
region and could crash the QEMU process (e.g. under ASan).

Fix it by double-checking cursor->chunk.data_size for the correct size.

This patch is based on the suggested changes by the reporter in the bug
ticket.

Reported-by: huntr bubble
Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3646
Signed-off-by: Thomas Huth <thuth@redhat.com>
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20260630101022.379057-1-thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
(cherry picked from commit 0e51b71c7b7706923536c1f7923cace82877932b)
---
 hw/display/qxl-render.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/hw/display/qxl-render.c b/hw/display/qxl-render.c
index c6a9ac1da10..1fe63b6f5ca 100644
--- a/hw/display/qxl-render.c
+++ b/hw/display/qxl-render.c
@@ -272,9 +272,11 @@ static QEMUCursor *qxl_cursor(PCIQXLDevice *qxl, QXLCursor *cursor,
     case SPICE_CURSOR_TYPE_MONO:
         /* Assume that the full cursor is available in a single chunk. */
         size = 2 * cursor_get_mono_bpl(c) * c->height;
-        if (size != cursor->data_size) {
-            fprintf(stderr, "%s: bad monochrome cursor %ux%u with size %u\n",
-                    __func__, c->width, c->height, cursor->data_size);
+        if (size != cursor->data_size || cursor->chunk.data_size < size) {
+            qxl_set_guest_bug(qxl, "%s: bad monochrome cursor %ux%u"
+                              " data_size %u chunk_size %u",
+                              __func__, c->width, c->height,
+                              cursor->data_size, cursor->chunk.data_size);
             goto fail;
         }
         and_mask = cursor->chunk.data;
-- 
2.53.0