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([213.152.188.86]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c2080cc2bddsm297087866b.42.2026.08.09.15.48.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 09 Aug 2026 15:48:12 -0700 (PDT) From: Aldo Ariel Panzardo To: Zack Rusin Cc: bcm-kernel-feedback-list@broadcom.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Aldo Ariel Panzardo Subject: [PATCH v2] drm/vmwgfx: return an error when a shared GB surface has no backup buffer Date: Sun, 9 Aug 2026 19:48:00 -0300 Message-ID: <20260809224800.771632-1-qwe.aldo@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit vmw_gb_surface_reference_internal() rejects a surface that has no backup buffer by logging an error and jumping to out_bad_resource, but it never sets ret on that path. ret is still 0 from the earlier successful vmw_surface_handle_reference(), so the ioctl returns success while leaving the reply structure uninitialised. drm_ioctl() then copies the 72-byte reply back to user space; on a CONFIG_INIT_STACK_NONE build that is an information leak of stale stack contents, and on every build user space is handed a "successful" reply that was never produced. DRM_VMW_GB_SURFACE_REF is DRM_RENDER_ALLOW, so an unprivileged local user can reach it. Set ret to -EINVAL and, on the error paths, drop the reference that vmw_surface_handle_reference() took; once the ioctl fails user space no longer releases it via DRM_VMW_UNREF_SURFACE. The unref is guarded by ret so the shared success fall-through keeps the reference the caller still owns, and it also plugs the same leak on the drm_gem_handle_create() failure path. Fixes: 14b1c33e8429 ("drm/vmwgfx: Add new ioctl for GB surface create and reference") Cc: stable@vger.kernel.org Suggested-by: Zack Rusin Signed-off-by: Aldo Ariel Panzardo --- v2: - Shortened the commit message (Zack Rusin). - Also drop the reference taken by vmw_surface_handle_reference() on the error paths; with the ioctl now returning an error, user space no longer releases it via DRM_VMW_UNREF_SURFACE (Zack Rusin). This also plugs the same pre-existing leak on the drm_gem_handle_create() path. v1: https://lore.kernel.org/all/20260808231002.67559-1-qwe.aldo@gmail.com/ drivers/gpu/drm/vmwgfx/vmwgfx_surface.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c index bd0563741e..164886a3e6 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c @@ -1720,6 +1720,7 @@ vmw_gb_surface_reference_internal(struct drm_device *dev, srf = &user_srf->srf; if (!srf->res.guest_memory_bo) { DRM_ERROR("Shared GB surface is missing a backup buffer.\n"); + ret = -EINVAL; goto out_bad_resource; } metadata = &srf->metadata; @@ -1758,6 +1759,9 @@ vmw_gb_surface_reference_internal(struct drm_device *dev, rep->creq.must_be_zero = 0; out_bad_resource: + if (ret) + ttm_ref_object_base_unref(vmw_fpriv(file_priv)->tfile, + base->handle); ttm_base_object_unref(&base); return ret; -- 2.43.0