From 6b59bd9eea08dea84df61bfa847579f14213684c Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Tue, 19 Jan 2021 14:03:18 +0100 Subject: drm/syncobj: Fix use-after-free MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit commit a37eef63bc9e16e06361b539e528058146af80ab upstream. While reviewing Christian's annotation patch I noticed that we have a user-after-free for the WAIT_FOR_SUBMIT case: We drop the syncobj reference before we've completed the waiting. Of course usually there's nothing bad happening here since userspace keeps the reference, but we can't rely on userspace to play nice here! Signed-off-by: Daniel Vetter Fixes: bc9c80fe01a2 ("drm/syncobj: use the timeline point in drm_syncobj_find_fence v4") Reviewed-by: Christian König Cc: Christian König Cc: Lionel Landwerlin Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Thomas Zimmermann Cc: David Airlie Cc: Daniel Vetter Cc: dri-devel@lists.freedesktop.org Cc: # v5.2+ Link: https://patchwork.freedesktop.org/patch/msgid/20210119130318.615145-1-daniel.vetter@ffwll.ch Signed-off-by: Greg Kroah-Hartman --- drivers/gpu/drm/drm_syncobj.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c index 4b5c7b0ed714..8fdb27135406 100644 --- a/drivers/gpu/drm/drm_syncobj.c +++ b/drivers/gpu/drm/drm_syncobj.c @@ -326,19 +326,18 @@ int drm_syncobj_find_fence(struct drm_file *file_private, return -ENOENT; *fence = drm_syncobj_fence_get(syncobj); - drm_syncobj_put(syncobj); if (*fence) { ret = dma_fence_chain_find_seqno(fence, point); if (!ret) - return 0; + goto out; dma_fence_put(*fence); } else { ret = -EINVAL; } if (!(flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT)) - return ret; + goto out; memset(&wait, 0, sizeof(wait)); wait.task = current; @@ -370,6 +369,9 @@ int drm_syncobj_find_fence(struct drm_file *file_private, if (wait.node.next) drm_syncobj_remove_wait(syncobj, &wait); +out: + drm_syncobj_put(syncobj); + return ret; } EXPORT_SYMBOL(drm_syncobj_find_fence); -- cgit v1.2.3