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Tue, 28 Jul 2026 13:44:55 -0700 (PDT) From: Ankur Saini Date: Wed, 29 Jul 2026 02:14:24 +0530 Subject: [PATCH v2] virtio-gpu: reject requests with short/truncated control headers MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260729-virtio-gpu-short-header-v2-1-18036a97219a@gmail.com> X-B4-Tracking: v=1; b=H4sIAAAAAAAC/4WNQQ6CMBBFr0Jm7Zi2IaCuvIdhMdKBTiLUTLHRE O5u5QIu30v++yskVuEEl2oF5SxJ4lzAHSroA80jo/jC4IxrTOtOmEUXiTg+X5hC1AUDk2fFum2 IrCeuhxbK+qk8yHsv37rCQdIS9bMfZfuz/5vZokUa7JmMuVtj/HWcSB7HPk7Qbdv2BXneVAS+A AAA X-Change-ID: 20260728-virtio-gpu-short-header-476aa1dae4f7 To: qemu-devel@nongnu.org Cc: =?utf-8?q?Alex_Benn=C3=A9e?= , Akihiko Odaki , Dmitry Osipenko , "Michael S. Tsirkin" , =?utf-8?q?Marc-Andr=C3=A9_Lureau?= , Stefano Garzarella , Ankur Saini X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1785271491; l=3552; i=ankur98saini@gmail.com; s=20260728; h=from:subject:message-id; bh=MM5LFpD2vK4p0vGwklanlLhmAWMaXRot2mtQBQ3akmU=; b=WN686dLBMhrl8pwHl7JUS85vT4SOBD6d0cp07WwGaXalHAdFV+nz6Zmnfhpk0o+EbBg6YDs5h tosn+5vWGx7C/jbqATTpH3xtd1fNgK2iw/smq/ET16HdXriHNEYuOOa X-Developer-Key: i=ankur98saini@gmail.com; a=ed25519; pk=fiA1ENLrWfuTIKes9f/fn/hIbq1fqEHYxopa8LdM/8s= 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=2607:f8b0:4864:20::42b; envelope-from=ankur98saini@gmail.com; helo=mail-pf1-x42b.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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 @gmail.com) X-ZM-MESSAGEID: 1785271533587158500 A control request shorter than virtio_gpu_ctrl_hdr can leave cmd_hdr partially initialized. If the supplied bytes set the fence flag, stale fence metadata may later be returned to the guest. The vhost-user-gpu backend has the same issue: it logs a short header copy but continues to process the partially initialized command. Validate the common header length before dispatch in both paths. Clear cmd_hdr and complete malformed requests with ERR_INVALID_PARAMETER so stale fields cannot reach the response. Fixes: CVE-2026-18054 Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4094 Reported-by: Ankur Saini Suggested-by: Akihiko Odaki Signed-off-by: Ankur Saini Reviewed-by: Marc-Andr=C3=A9 Lureau --- Changes in v2: - Also reject short/truncated control headers in vhost-user-gpu. - Expand the commit message to describe both affected paths. - Link to v1: https://lore.kernel.org/qemu-devel/20260728-virtio-gpu-short-= header-v1-1-af19a00b100d@gmail.com --- contrib/vhost-user-gpu/vhost-user-gpu.c | 21 ++++++++++++--------- hw/display/virtio-gpu.c | 10 ++++++++-- 2 files changed, 20 insertions(+), 11 deletions(-) diff --git a/contrib/vhost-user-gpu/vhost-user-gpu.c b/contrib/vhost-user-g= pu/vhost-user-gpu.c index bb41758e34..8149834745 100644 --- a/contrib/vhost-user-gpu/vhost-user-gpu.c +++ b/contrib/vhost-user-gpu/vhost-user-gpu.c @@ -924,16 +924,19 @@ vg_handle_ctrl(VuDev *dev, int qidx) if (len !=3D sizeof(cmd->cmd_hdr)) { g_warning("%s: command size incorrect %zu vs %zu\n", __func__, len, sizeof(cmd->cmd_hdr)); - } - - virtio_gpu_ctrl_hdr_bswap(&cmd->cmd_hdr); - g_debug("%d %s\n", cmd->cmd_hdr.type, - vg_cmd_to_string(cmd->cmd_hdr.type)); - - if (vg->virgl) { - vg_virgl_process_cmd(vg, cmd); + memset(&cmd->cmd_hdr, 0, sizeof(cmd->cmd_hdr)); + vg_ctrl_response_nodata( + vg, cmd, VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER); } else { - vg_process_cmd(vg, cmd); + virtio_gpu_ctrl_hdr_bswap(&cmd->cmd_hdr); + g_debug("%d %s\n", cmd->cmd_hdr.type, + vg_cmd_to_string(cmd->cmd_hdr.type)); + + if (vg->virgl) { + vg_virgl_process_cmd(vg, cmd); + } else { + vg_process_cmd(vg, cmd); + } } =20 if (cmd->state !=3D VG_CMD_STATE_FINISHED) { diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c index 4d46a4eb10..15a845eff6 100644 --- a/hw/display/virtio-gpu.c +++ b/hw/display/virtio-gpu.c @@ -1105,8 +1105,14 @@ void virtio_gpu_process_cmdq(VirtIOGPU *g) break; } =20 - /* process command */ - vgc->process_cmd(g, cmd); + if (unlikely(iov_size(cmd->elem.out_sg, cmd->elem.out_num) < + sizeof(cmd->cmd_hdr))) { + memset(&cmd->cmd_hdr, 0, sizeof(cmd->cmd_hdr)); + virtio_gpu_ctrl_response_nodata( + g, cmd, VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER); + } else { + vgc->process_cmd(g, cmd); + } =20 /* command suspended */ if (!cmd->finished && !(cmd->cmd_hdr.flags & VIRTIO_GPU_FLAG_FENCE= )) { --- base-commit: 299e7557ed15a9a325620698add379a3ce2d1d95 change-id: 20260728-virtio-gpu-short-header-476aa1dae4f7 Best regards, --=20 Ankur Saini