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Tue, 04 Aug 2026 00:25:46 -0700 (PDT) From: Ankur Saini Date: Tue, 04 Aug 2026 12:55:32 +0530 Subject: [PATCH v4] 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: <20260804-virtio-gpu-short-header-v4-1-b3e30a81e347@gmail.com> X-B4-Tracking: v=1; b=H4sIAAAAAAAC/4XPwQqDMAwG4FeRntfRVqm6095j7JBp1MBcpXVlQ 3z3RS+Tgez4h/xfyCQCesIgTskkPEYK5B4cskMiqg4eLUqqOQujjFW5KWQkP5KT7fCUoXN+lB1 CjV5muQXQNWDW5ILbg8eGXqt8uXLuKIzOv9dDUS/T/2bUUktodAlK3bRS9bntge7HyvViMaPZO uW+Y9jRhUotlLlh7tdJvw5v7TspO2VqK/4TCrR668zz/AGzH96jTgEAAA== 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=1785828342; l=5428; i=ankur98saini@gmail.com; s=20260728; h=from:subject:message-id; bh=GavOz8unD44YHrwDnmuR9qdr/QDj3La38GjPNZkKj7w=; b=/frHavuZgnp4jf+aFXBLR96X/6EiIWB5xeK5+iczgpwz5i5xHtas5m3xFJkRpKb1HUBdSNCQ2 qz9eQboOcBQB6Jf0+EjJb93m35NFydeDUQKi4KtwqfV1mCrLutg1Del 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::62f; envelope-from=ankur98saini@gmail.com; helo=mail-pl1-x62f.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: 1785828373480158500 A short control request can leave command data partially initialized. For the common header, guest-controlled flags can then cause stale fence metadata to be returned to the guest. The command fill helpers detect a short copy but only log and return, leaving the malformed request without an error. However, virtio_gpu_simple_process_cmd() and vg_process_cmd() actually complete it, though its response type is VIRTIO_GPU_RESP_OK_NODATA. Make VIRTIO_GPU_FILL_CMD() clear the partially copied object and complete the request with ERR_INVALID_PARAMETER. Make VUGPU_FILL_CMD() report the same error through the existing vhost-user-gpu dispatcher. This also rejects truncated type-specific commands. The vhost-user-gpu common header is copied outside VUGPU_FILL_CMD(), so clear it and complete the request directly when that copy is short. Fixes: CVE-2026-18054 Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4094 Reported-by: Ankur Saini Suggested-by: Akihiko Odaki Reviewed-by: Akihiko Odaki Signed-off-by: Ankur Saini --- Changes in v4: - Correct the commit message to note that type-specific malformed requests were completed with VIRTIO_GPU_RESP_OK_NODATA. - Link to v3: https://lore.kernel.org/qemu-devel/20260803-virtio-gpu-short-= header-v3-1-936c1daa8e61@gmail.com Changes in v3: - Handle short copies in VIRTIO_GPU_FILL_CMD() and VUGPU_FILL_CMD(), also rejecting truncated type-specific commands. - Clear partially copied QEMU command data before completing the error. - Keep vhost-user-gpu's explicit common-header check and drop the redundant virtio_gpu_process_cmdq() check. - Rebase onto current master. - Link to v2: https://lore.kernel.org/qemu-devel/20260729-virtio-gpu-short-= header-v2-1-18036a97219a@gmail.com 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 ++++++++++++--------- contrib/vhost-user-gpu/vugpu.h | 1 + include/hw/virtio/virtio-gpu.h | 3 +++ 3 files changed, 16 insertions(+), 9 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/contrib/vhost-user-gpu/vugpu.h b/contrib/vhost-user-gpu/vugpu.h index 2374eb90cb..aaf2870cb2 100644 --- a/contrib/vhost-user-gpu/vugpu.h +++ b/contrib/vhost-user-gpu/vugpu.h @@ -179,6 +179,7 @@ struct virtio_gpu_ctrl_command { if (vugpufillcmd_s_ !=3D sizeof(out)) { \ g_critical("%s: command size incorrect %zu vs %zu", \ __func__, vugpufillcmd_s_, sizeof(out)); \ + cmd->error =3D VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER; \ return; \ } \ } while (0) diff --git a/include/hw/virtio/virtio-gpu.h b/include/hw/virtio/virtio-gpu.h index 2f60c72078..f965defa6b 100644 --- a/include/hw/virtio/virtio-gpu.h +++ b/include/hw/virtio/virtio-gpu.h @@ -315,6 +315,9 @@ struct VirtIOGPURutabaga { qemu_log_mask(LOG_GUEST_ERROR, \ "%s: command size incorrect %zu vs %zu\n", \ __func__, virtiogpufillcmd_s_, sizeof(out)); \ + memset(&out, 0, sizeof(out)); \ + virtio_gpu_ctrl_response_nodata( \ + g, cmd, VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER); \ return; \ } \ } while (0) --- base-commit: b428fe036233cbd15d37e3c027ab6ca4d3661a80 change-id: 20260728-virtio-gpu-short-header-476aa1dae4f7 Best regards, --=20 Ankur Saini