From: David Herrmann Date: Mon, 26 Aug 2013 13:16:49 +0000 (+0200) Subject: drm: fix DRM_IOCTL_MODE_GETFB handle-leak X-Git-Tag: v3.2.66~11 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=125f21f38d448ae04aae1a665147faf1263a4736 drm: fix DRM_IOCTL_MODE_GETFB handle-leak commit 101b96f32956ee99bf1468afaf572b88cda9f88b upstream. DRM_IOCTL_MODE_GETFB is used to retrieve information about a given framebuffer ID. It is a read-only helper and was thus declassified for unprivileged access in: commit a14b1b42477c5ef089fcda88cbaae50d979eb8f9 Author: Mandeep Singh Baines Date: Fri Jan 20 12:11:16 2012 -0800 drm: remove master fd restriction on mode setting getters However, alongside width, height and stride information, DRM_IOCTL_MODE_GETFB also passes back a handle to the underlying buffer of the framebuffer. This handle allows users to mmap() it and read or write into it. Obviously, this should be restricted to DRM-Master. With the current setup, *any* process with access to /dev/dri/card0 (which means any process with access to hardware-accelerated rendering) can access the current screen framebuffer and modify it ad libitum. For backwards-compatibility reasons we want to keep the DRM_IOCTL_MODE_GETFB call unprivileged. Besides, it provides quite useful information regarding screen setup. So we simply test whether the caller is the current DRM-Master and if not, we return 0 as handle, which is always invalid. A following DRM_IOCTL_GEM_CLOSE on this handle will fail with EINVAL, but we accept this. Users shouldn't test for errors during GEM_CLOSE, anyway. And it is still better as a failing MODE_GETFB call. v2: add capable(CAP_SYS_ADMIN) check for compatibility with i-g-t Signed-off-by: David Herrmann Reviewed-by: Chris Wilson Signed-off-by: Dave Airlie [bwh: Backported to 3.2: - drm_framebuffer_funcs::create_handle must be non-null - Adjust context, indentation] Signed-off-by: Ben Hutchings --- diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c index 3f1799b52d06..09851ce2500e 100644 --- a/drivers/gpu/drm/drm_crtc.c +++ b/drivers/gpu/drm/drm_crtc.c @@ -1815,7 +1815,17 @@ int drm_mode_getfb(struct drm_device *dev, r->depth = fb->depth; r->bpp = fb->bits_per_pixel; r->pitch = fb->pitch; - fb->funcs->create_handle(fb, file_priv, &r->handle); + if (file_priv->is_master || capable(CAP_SYS_ADMIN)) { + ret = fb->funcs->create_handle(fb, file_priv, &r->handle); + } else { + /* GET_FB() is an unprivileged ioctl so we must not + * return a buffer-handle to non-master processes! For + * backwards-compatibility reasons, we cannot make + * GET_FB() privileged, so just return an invalid handle + * for non-masters. */ + r->handle = 0; + ret = 0; + } out: mutex_unlock(&dev->mode_config.mutex);