On 2026/07/24 13:01, [email protected] wrote:
From: Marc-André Lureau <[email protected]>
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.
fbend is computed from the same wrapped fb->offset that is later used
for data + fb->offset. Since fbend is checked against blob_size, the
wrapped pointer and scanout extent remain within the blob. Wraparound
can select a different in-bounds region, but the described host
out-of-bounds access does not follow.
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 <[email protected]>
Signed-off-by: Marc-André Lureau <[email protected]>
---
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_framebuffer *fb,
struct virtio_gpu_set_scanout_blob *ss,
uint64_t blob_size)
{
- uint64_t fbend;
+ uint64_t fbend, offset;
uint32_t bytes_pp;
fb->format = 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;
}
- fb->offset = ss->offsets[0] + ss->r.x * bytes_pp + ss->r.y * fb->stride;
+ offset = (uint64_t)ss->offsets[0] + (uint64_t)ss->r.x * bytes_pp +
+ (uint64_t)ss->r.y * fb->stride;
- fbend = fb->offset;
- fbend += (uint64_t) fb->stride * ss->r.height;
+ fbend = offset + (uint64_t)fb->stride * ss->r.height;
- 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;
}
+ fb->offset = offset;
+
return true;
}
This patch does not apply to master and appears to be based on:
Based-on: <[email protected]>
("[PATCH] hw/display/virtio-gpu: Remove the bytes_pp field")
The dependency is not declared. Please record the prerequisite.
Regards,
Akihiko Odaki
